8. plant systematics and evolution

Levetin−McMahon: Plants II. Introduction to Plant 8. Plant Systematics and © The McGraw−Hill
and Society, Fifth Edition Life: Botanical Principles Evolution Companies, 2008

C H A PT E R OU T L I N E
Early History of Classification 124
Carolus Linnaeus 124
How Plants are Named 126
Common Names 126
A CLOSER LOOK 8.1 The Language
of Flowers 128
Scientific Names 129
Taxonomic Hierarchy 130
Higher Taxa 130
What Is a Species? 131
A CLOSER LOOK 8.2 Saving
Species Through Systematics 133
The Influence of Darwin’s Theory
of Evolution 134
The Voyage of the HMS Beagle 134
Natural Selection 136
Phylocode 137
Chapter Summary 137
Review Questions 137
Further Reading 138

K EY C O N CE P T S
1. Scientific names are two-word names
called binomials that are internationally
recognized by the scientific community.
2. Carolus Linnaeus, an eighteenth-century
Swedish botanist, started the binomial
system and is therefore known as the
Father of Taxonomy.
3. With the publication in 1859 of On
the Origin of Species, Charles Darwin
proposed that species are not static
entities but are works in progress that
evolve in response to environmental
pressures.
4. Natural selection favors the survival
and reproduction of those individuals in C H A P T E R
a species that possess traits that better
adapt them to a particular environment.

8
Plant Systematics
and Evolution
Fossils, such as this 160 million year old arucarian pine cone from
Argentina, were part of the evidence Charles Darwin used to formulate
his theory of evolution of species by means of natural selection. 123


124 UNIT II Introduction to Plant Life: Botanical Principles

P
lant systematics is the branch of botany that is con- Carolus Linnaeus (fig. 8.1) was born in May 1707, in
cerned with the naming, identification, evolution, and southern Sweden, the son of a clergyman. He became inter-
classification (arrangement into groups with common ested in botany at a very young age through the influence of
characteristics) of plants. In a strict sense, plant taxonomy his father, who was an avid gardener and amateur botanist. It
is the science of naming and classifying plants; however, in was expected that Linnaeus would also become a clergyman,
this book the terms taxonomy and systematics are used inter- but in school he did not do well in theological subjects. He
changeably. The simplest form of classification is a system did, however, excel in the natural sciences and entered the
based on need and use; early humans undoubtedly classified University of Lund in 1727 to pursue studies in natural sci-
plants into edible, poisonous, medicinal, and hallucinogenic ence and medicine. (At this time medical schools were the
categories. centers of botanical study because physicians were expected
to know the plant sources of medicines in use.) After one year
he transferred to the University of Uppsala, the most presti-
EARLY HISTORY OF gious university in Sweden. It was here that he published his
CLASSIFICATION first botanical papers, which laid the foundations for his later
works in classification and plant sexuality. In 1732, he under-
The earliest known formal classification was proposed by
took a solo expedition to Lapland to catalog the natural his-
the Greek naturalist Theophrastus (370–285 B.C.), who was a
tory of this relatively unknown area. He later published Flora
student of Aristotle. In his botanical writings (Enquiries into
Lapponica, a detailed description of the plants of this area.
Plants and The Causes of Plants), he described and classified
Linnaeus received his medical degree in 1735 from the
approximately 500 species of plants into herbs, undershrubs,
University of Harderwijk in the Netherlands. Soon he came
shrubs, and trees. Because his influence extended through the
under the patronage of George Clifford, a director of the Dutch
Middle Ages, he is regarded as the Father of Botany.
East India Company and one of the wealthiest men in Europe.
Two Roman naturalists who also had long-lasting impacts
He served as Clifford’s personal physician and as curator
on plant taxonomy were Pliny the Elder (A.D. 23–79) and
of his magnificent gardens, which housed specimens from
Dioscorides (first century A.D.). Both described medicinal
around the world. The 3 years he spent in the Netherlands
plants in their writings, and Dioscorides’s Materia Medica
remained the standard medical reference for 1,500 years.
From this period through the Middle Ages, little new botani-
cal knowledge was added. Blind adherence to the Greek and
Roman classics prevailed, using manuscripts painstakingly
copied by hand in monasteries throughout Europe.
The revival of botany after its stagnation in the Middle
Ages began early in the Renaissance with the renewed inter-
est in science and other fields of study. The invention of the
printing press in the middle of the fifteenth century allowed
botanical works to be more easily produced than ever before.
These richly illustrated books, known as herbals, dealt largely
with medicinal plants and their identification, collection, and
preparation. The renewal of interest in taxonomy can be traced
to the work of several herbalists; in fact, this period of botanical
history from the fifteenth through the seventeenth centuries is
known as the Age of Herbals. Another factor in the revival of
taxonomy was the global exploration by the Europeans during
this period, which led to the discoveries of thousands of new
plant species. In less than 100 years more plants were intro-
duced to Europe than in the previous 2,000 years.

Carolus Linnaeus
By the beginning of the eighteenth century, it was common
to name plants using a polynomial (see fig. 8.4), which
included a single word name for the plant (today called the
genus name), followed by a lengthy list of descriptive terms,
all in Latin. This system had flaws. It was not standardized;
different polynomials existed for the same plant; and it was
cumbersome to remember some of the longer polynomials, Figure 8.1 Statue of Carolus Linnaeus (1707–1778) holding
which could be a paragraph in length. This was the state of flowers of Indian blanket (Gaillardia pulchella) at the Linnaeus
taxonomy during the time of Linnaeus. Teaching Garden, Tulsa, OK.


CHAPTER 8 Plant Systematics and Evolution 125

He returned to Sweden in 1738 and soon married Sara
Elisabeth Moraea. After setting up a medical practice in
Stockholm, he was appointed physician to the Swedish
Admiralty, specializing in the treatment of venereal diseases.
In 1741, he returned to the University of Uppsala as professor
of medicine and botany, a position he retained until retire-
ment in 1775. Linnaeus was a popular teacher who attracted
students from all over Europe. Many of his students became
famous professors in their own right; others traveled to distant
lands collecting unknown specimens for Linnaeus to classify.
After suffering several strokes, he died in January 1778.
One of Linnaeus’s achievements was his sexual system of
plant classification, which did much to popularize the study of
botany. This system was based on the number, arrangement,
Figure 8.2 Frontispiece of Systema Naturae, one of the writings and length of stamens and thus divided flowering plants into
of Linnaeus, in which he expounded on his ideas of classification. 24 classes. Using this system, it was possible for anyone
to identify and name unknown plants. At the time, his lan-
guage was risqué because he compared floral parts to human
were the most productive period in his life. During that time, sexuality, with stamens referred to as husbands and pistils∗
he completed several books and papers including Systema as wives; for example, “husband and wife have the same
Naturae, Fundamenta Botanica, and Genera Plantarum, bed” meant stamens and pistils in the same flower (fig. 8.3).
which expanded on his ideas of classification (fig. 8.2). ∗ Note that the older term of pistil, rather than carpel, has been used in this key.

Vegetable Kingdom
Key of the Sexual System

Marriages of plants
Florescence
Public marriages
Flowers visible to every one
In one bed
Husband and wife have the same bed
All the flowers hermaphrodite: stamens and pistils in the same flower
Without affinity
Husbands not related to each other
Stamens not joined together in any part
With equality
All the males of equal rank
Stamens have no determinate proportion of length
1. One male 4. Four males 7. Seven males 10. Ten males
2. Two males 5. Five males 8. Eight males 11. Twelve males
3. Three males 6. Six males 9. Nine males 12. Twenty males
13. Many males
With subordination
Some males above others
Two stamens are always lower than the others
14. Two powers 15. Four powers
With affinity
Husbands related to each other
Stamens cohere with each other, or with the pistil
16. One brotherhood 18. Many brotherhoods
17. Two brotherhoods 19. Confederate males
In two beds 20. Feminine males
Husband and wife have separate beds (b)
Male flowers and female flowers in the same species
21. One house 22. Two houses 23. Polygamies
Clandestine marriages
Flowers scarce visible to the naked eye
(a) 24. Clandestine marriages

Figure 8.3 (a) Linnaeus’s sexual system related floral parts to human sexuality. (b) Hibiscus in the Mallow Family (Malvaceae) keys out to
feminine males because the stamens are attached to the style.



Dr. Johann Siegesbeck, a contemporary of Linnaeus and
director of the botanical garden in St. Petersburg, was
shocked at the analogies and said such

loathsome harlotry as several males to one female
would not be permitted in the vegetable kingdom
by the Creator . . . . Who would have thought that
bluebells, lilies, and onions could be up to such
immorality?

Despite the opposition of some, the Linnaean sexual
method was easy to understand and simple for even the ama-
teur botanist to use. This method, however, was an artificial
system grouping together clearly unrelated plants (in his sys-
tem, cherries and cacti were grouped together); by the early
nineteenth century it was abandoned in favor of systems that
reflected natural relationships among plants.
Linnaeus’s greatest accomplishment was his adoption
and popularization of a binomial system of nomenclature.
When he described new plants, he conformed to the current
practice of using a polynomial. For convenience, however, he
began to add in the margin a single descriptive adjective that
would identify unequivocally a particular species (fig. 8.4).
He called this adjective the trivial name. This combination
later developed into the two-word scientific name, or bino-
mial, described in the next section. Linnaeus used this system
consistently in Species Plantarum, published in 1753. This
work contains descriptions and names of 5,900 plants, all the
plants known to Linnaeus. The binomial system simplified
scientific names and was soon in wide use. In 1867, a group
of botanists at the International Botanical Congress in Paris
established rules governing plant nomenclature and classifi-
cation. They established Species Plantarum as the starting
point for scientific names. Although the rules (formalized Figure 8.4 A photograph from Species Plantarum illustrates the
in the International Code of Botanical Nomenclature) have beginning of the binomial system. Note the trivial names in the
been modified over the years, the 1753 date is still valid, margin next to the polynomial description for each species. The
trivial name was later designated as the species epithet, which,
and many names first proposed by Linnaeus are still in use together with the generic, forms the binomial.
today.
Linnaeus’s contributions were not limited to botany since
the binomial system is used for all known organisms. He is Common Names
credited with naming approximately 12,000 plants and ani- A close look at common names often reveals a keen sense of
mals; for all his contributions to the field of taxonomy, he is observation, a fanciful imagination, or even a sense of humor:
known as the Father of Taxonomy. trout lily, milkweed, Dutchman’s pipe, Texas bluebonnet,
ragged sailor, and old maid’s nightcap (table 8.1). Sometimes
the names even convey feelings or emotions (see A Closer
Look 8.1—The Language of Flowers).
HOW PLANTS ARE NAMED Names have evolved over centuries but are sometimes
Names are useful because they impart some information only used in a limited geographical area. Even short dis-
about a plant; it may be related to flower color, leaf shape, fla- tances away, other common names may be used for the
vor, medicinal value, season of blooming, or location. Names same plant. Consider, for example, the many names for the
are necessary for communication; “if you know not the name, tree that many people call osage orange (Maclura pomifera)
knowledge of things is wasted.” (fig. 8.5a): bodeck, bodoch, bois d’arc, bow-wood, osage
This discussion begins with a look at common names, or apple tree, hedge, hedge apple, hedge osage, hedge-plant
what plants are called locally, and follows with an examina- osage, horse apple, mock orange, orange-like maclura, osage
tion of internationally recognized scientific names. apple, and wild orange.



Table 8.1 Some Common Names
and Their Meanings

Names in Commemoration
Douglas-fir David Douglas, plant collector
(1798–1834)
Camellia Georg Josef Kamel, pharmacist
(1661–1706)
Gerber daisy Traugott Gerber, German explorer
(?–1743)
Freesia Friedrich H. T. Freese, German
physician (?–1876)
(a)
Names That Describe Physical Qualities
Dusty miller White woolly leaves
Dutchman’s breeches Shape of flower
Goldenrod Shape and color of inflorescence
Indian pipe Shape of flower with stem
Cattail Inflorescence of carpellate flowers
Lady’s slipper Shape of this orchid’s flower
Milkweed Milky juice when plant is cut
Skunk cabbage Fetid odor of inflorescence
Cheeses Fruit resembles a round head of cheese
Smoke tree Plumelike pedicels
Shagbark hickory Shedding bark
Redbud Color of flower buds
Quaking aspen Rustling leaves
Bluebell Color and shape of flower
Crape myrtle Wavy edges of petals

Scientific Names That Have Become Common Names
Hydrangea Abelia
Vanilla Narcissus
Coreopsis Gladiolus

Names That Indicate Use
Daisy fleabane Gets rid of fleas
Boneset A tonic from this plant can heal bones
Feverwort Medicinal property to reduce fever
Kentucky coffee tree Seeds roasted for coffee substitute (b)
Belladonna Juice used to beautify by producing
pallid skin and dilated, mysterious eyes Figure 8.5 Mock orange is a common name shared by (a) the
tree Maclura pomifera and (b) the shrub Philadelphus lewisii—two
Names That Indicate Origin, Location, or Season entirely different species of plants.
Pacific yew Grows along northern Pacific coast
Spring beauty One of the first flowers of spring
Marshmallow Found in wet, marshy habitat
Daylily Flowers last only a day
Four-o’clock Flowers open in late afternoon
Japanese honeysuckle Country of origin is Japan


A CLOSER LOOK 8.1
The Language of Flowers

Through traditions, some flowers became symbolic of
certain emotions and feelings. This was sometimes even
reflected in their common names; two straightforward
examples are forget-me-not flowers, which conveyed the
sentiment “remember me,” and bachelor’s button, which
indicated the single status of the wearer. This symbolism
reached its peak during the Victorian era, when almost every
flower and plant had a special meaning. In Victorian times, it
was possible to construct a bouquet of flowers that imparted
a whole message (box fig. 8.1). A Victorian suitor might send
a bouquet of jonquils, white roses, and ferns to his intended,
which indicated that he desired a return of affection, he was
worthy of her love, and he was fascinated by her. This “lan-
guage” became so popular that dictionaries were printed to
interpret floral meanings. One of the most popular dictionar-
ies was the Language of Flowers (1884) by Kate Greenaway,
a well-known illustrator of children’s books. Following is a
small sampling of some common flowers and plants and what
they symbolized:
Amaryllis: pride
Apple blossom: preference
Bachelor’s buttons: celibacy
Bluebell: constancy
Buttercup: ingratitude
Yellow chrysanthemum: slighted love
Daffodil: regard
Daisy: innocence Box Figure 8.1 Flowers convey a message all their own.
Dogwood: durability
Elm: dignity
Goldenrod: caution
Dwarf sunflower: adoration
Holly: foresight
Tall sunflower: haughtiness
Honeysuckle: generous and devoted affection
Yellow tulip: hopeless love
Ivy: fidelity
Blue violet: faithfulness
Lavender: distrust
Wild grape: charity
Lichen: dejection
Zinnia: thought of absent friends
Lily of the valley: return of happiness
Live oak: liberty Even today, several plants have well-known symbolic
Magnolia: love of nature meanings. Red roses convey passionate love; a four-leaf clo-
Marigold: grief ver means luck; orange blossoms symbolize weddings; and
Mock orange: counterfeit an olive branch indicates peace. Floral colors can also com-
Oak leaves: bravery municate feelings, with red indicating passion; blue, security;
Palm: victory yellow, cheer; white, sympathy; and orange, friendship. With
Pansy: thoughts some thought, it is possible to find the right flower and color
Spring crocus: youthful gladness to express the exact message.

128



On the other hand, different plants may share the same
common name. Although mock orange is one of the common Table 8.2
names for osage orange, the name mock orange is usually Genus Names and Their Meanings
associated with a completely unrelated group of flowering
shrubs (Philadelphus spp.) (fig. 8.5b). These examples point Names in Commemoration
out the difficulties with common names; one plant may be
Begonia Michel Begon, patron of botany (1638–1710)
known by several different names, and the same name may
apply to several different plants. The need to have one univer- Forsythia William Forsyth, gardener at Kensington
Palace (1737–1804)
sally accepted name is fulfilled with scientific names.
Bougainvillea Louis Antoine de Bougainville, explorer and
scientist (1729–1811)
Scientific Names Fuchsia Leonhard Fuchs, German physician and
Each kind of organism is known as a species, and similar spe- herbalist (1501–1566)
cies form a group called a genus (pl., genera). Each species Zinnia Johann Gottfried Zinn (1727–1759)
has a scientific name in Latin that consists of two elements;
Wisteria Caspar Wistar, American professor of plant
the first is the genus and the second is the specific epithet. anatomy (1761–1818)
Such a name is a binomial, literally two names, and is always
italicized or underlined; for example, Maclura pomifera is Names That Describe Physical Qualities
the scientific name for osage orange. A rough analogy of the Myriophyllum Finely divided leaves
binomial concept can be seen in a list of names in a telephone
Chlorophytum Green plant
directory, where the surname “Smith” (listed first) represents
the genus and the first names (John, Frank, and Mary) define Lunaria Moon, refers to appearance of pods
particular species within the genus. Helianthus Sunflower
In the binomial, the first name is a noun and is capital- Zebrina Zebra, refers to striped leaves
ized; the second, written in lower case, is usually an adjective. Trillium Floral parts in threes
After the first mention of a binomial, the genus name can be Tetrastigma Four-lobed stigma
abbreviated to its first letter, as in M. pomifera, but the spe- Ribes Acid tasting; refers to fruit
cific epithet can never be used alone. The genus name, how-
Polygonum Many knees; refers to jointed stems
ever, can be used alone, especially when referring to several
species within a genus; for example, Philadelphus refers to Zanthoxylum Yellow wood
over 50 species of mock orange. The specific epithet can be Sagittaria Arrow; refers to arrowhead leaves
replaced by an abbreviation for species, “sp.” (or “spp.” plu-
Names from Aboriginal or Classic Origins
ral), when the name of the species is unknown or unnecessary
for the discussion. In the previous example, Philadelphus sp. Avena Oats (Latin)
refers to one species of mock orange whereas Philadelphus Triticum Wheat (Latin)
spp. refers to more than one species. Allium Garlic (Greek)
Scientific names may be just as descriptive as common Catalpa Catalpa (North American Indian)
names, and translation of the Latin (or latinized Greek) is
Vitis Grape vine (Latin)
informative (table 8.2). Sometimes either the genus name or
Ulmus Elm (Latin)
the specific epithet is commemorative, derived from the name
of a botanist or other scientist. Some specific epithets are Pinus Pine (Latin)
frequently used with more than one genus, and knowledge of
Names That Indicate Use
their meanings will provide some insight into scientific names
encountered later in this text (table 8.3). Solidago Make whole or strengthen
A complete scientific name also includes the name or Angelica Angelic medicinal properties
names of the author or authors (often abbreviated) who first Cimcifuga Repel bugs
described the species or placed it in a particular genus. For Saponaria Soap; refers to soap that can be made from
example, the complete scientific name for corn is Zea mays the plant
L.; the “L” indicates that Linnaeus named this species. On the Pulmonaria Lung; used to treat infections of the lung
other hand, the complete name for osage orange is Maclura Potentilla Powerful; refers to its potent medicinal
pomifera (Raf.) Schneid. This author citation indicates that properties
Rafinesque-Schmaltz first described the species, giving it
Names That Indicate Location
the specific epithet pomifera, but Schneider later put it in the
Elodea Grows in marshes
genus Maclura. In this text, the author citations are omitted
for simplicity. Petrocoptis Break rock; refers to habit of growing in rock
crevices



A scientific name is unique, referring to only one spe-
Table 8.3 Common Scientific cies and universally accepted among scientists. It is the key
Epithets and Their Meanings to unlocking the door to the accumulated knowledge about
acidosus, -a, -um Sour a plant. Imagine the confusion if only common names were
aestivus, -a, -um Developing in summer used and a reference was made to mock orange. Would
albus, -a, -um White
this reference allude to Maclura pomifera or to a species of
Philadelphus?
alpinus, -a, -um Alpine
annus, -a, -um Annual
arabicus, -a, -um Of Arabia
arboreus, -a, -um Treelike
TAXONOMIC HIERARCHY
arvensis, -a, -um Of the field In addition to genus and species, other taxonomic categories
biennis, -a, -um Biennial
exist to conveniently group related organisms. As pointed out,
Linnaeus used an artificial system; however, today scientists
campester, -tris, -tre Of the pasture
use a phylogenetic system to group plants. In a phylogenetic
canadensis, -is, -e From Canada system, information is gathered from morphology, anatomy,
carolinianus, -a, -um From the Carolinas cell structure, biochemistry, genetics, and the fossil record to
chinensis, -is, -e From China determine evolutionary relationships and, therefore, natural
coccineus, -a, -um Scarlet groupings among plants.
deliciosus, -a, -um Delicious
dentatus, -a, -um Having teeth Higher Taxa
domesticus, -a, -um Domesticated Species that have many characteristics in common are
edulis, -is, -e Edible grouped into a genus, one of the oldest concepts in taxonomy
esculentus, -a, -um Tasty (fig. 8.6). In almost every society, the concept of genus has
europaeus, -a, -um From Europe developed in colloquial language; in English the words oak,
fetidus, -a, -um Bad smelling maple, pine, lily, and rose represent distinct genera. These
intuitive groupings reflect natural relationships based on
floridus, -a, -um Flowery
shared vegetative and reproductive characteristics. Many of
foliatus, -a, -um Leafy
the scientific names of genera are directly taken from the
hirsutus, -a, -um Hairy ancient Greek and Roman common names for these genera
japonicus, -a, -um From Japan (Quercus, old Latin word for oak).
lacteus, -a, -um Milky white The next higher category, or taxon (pl., taxa), above
littoralis, -is, -e Growing by the shore the rank of genus is the family. Families are composed of
luteus, -a, -um Yellow related genera that again (as in a genus) share combinations
of morphological traits. In the angiosperms, floral and fruit
mellitus, -a, -um Honey-sweet
features are often used to characterize a family. Ideally, the
niger, -ra, -um Black family represents a natural group with a common evolution-
occidentalis, -is, -e Western ary lineage; some families may be very small while others
odoratus, -a, -um Fragrant are very large, but still cohesive, groups. A few common
officinalis, -is, -e Used medicinally angiosperm families that have special economic importance
robustus, -a, -um Hardy are listed in Table 8.4. According to the International Code
ruber, -ra, -rum Red of Botanical Nomenclature, each family is assigned one
name, which is always capitalized and ends in the suffix
saccharinus, -a, -um Sugary
-aceae. The old established names of several well-known
sativus, -a, -um Cultivated families present exceptions to this rule. Both the tradi-
silvaticus, -a, -um Of the woods tional and standardized names are used for these families
sinensis, -is, -e Chinese (table 8.5). The taxa above the rank of family and their
speciosus, -a, -um Showy appropriate endings are presented in Table 8.6. The higher
tinctorius, -a, -um Used for dyeing the taxonomic category, the more inclusive the grouping
utilis, -is, -e Useful
(fig. 8.7). Families are grouped into orders, orders into
classes, classes into divisions (phyla)*, and divisions into
vernalis, -is, -e Spring flowering
kingdoms. A domain is above the kingdom level and is the
virginianus, -a, -um From Virginia
vulgaris, -is, -e Common *Either division or phylum (sing.; phyla, plural) may be used to indicate the taxonomic
rank that is composed of a group of related classes. Traditionally, division has been the
term preferred by botanists and will be used throughout this textbook.



(a) Quercus phellos (b) Quercus rubra
(willow oak) (red oak)

Figure 8.6 A genus is a group of species that share many characteristics in common. Although willow oak (Quercus phellos) and red oak
(Quercus rubra) are clearly distinct species, they are both recognizable as belonging to the oak (Quercus) genus by the presence of acorns.

most inclusive taxonomic category. The complete classifi- which defines a species as “a group of interbreeding popula-
cation of a familiar species is also illustrated in Table 8.6. tions reproductively isolated from any other such group of
In addition to the categories already described, biologists populations.”
also recognize intermediate categories with the “sub” This definition presents problems when defining plant
for any rank; for example, divisions may be divided into species. Many closely related plant species that are distinct
subdivisions, and species may be divided into subspecies morphologically are, in fact, able to interbreed; this is true
(varieties and forms are also categories below the rank of for many species of oaks and sycamores. By contrast, a
species). single plant species may have diploid and polyploid (more
Although the International Code of Botanical than the diploid number of chromosomes) individuals that
Nomenclature has rules that govern the assignment of names may be reproductively isolated from each other. It is esti-
and define the taxonomic hierarchy, it does not set forth any mated that as many as 40% of flowering plants may be
particular classification system. As a result, there are several polyploids, with the evening primrose group a thoroughly
organizational schemes that have supporters. These systems studied example; an even higher percentage of polyploid
differ in the numbers of classes, divisions, kingdoms, and even species occurs in ferns. Because of these limitations, alter-
domains and how they are related to one another. Presently natives to the biological species concept have been sug-
most biologists use a three-domain, six-kingdom system, gested. The ecological species concept recognizes a species
which will be described fully in Chapter 9. There is general through its role in the biological community as defined by
agreement about the use of a three-domain, six-kingdom sys- the set of unique adaptations within a particular species to
tem, but biologists still debate the definition of a species. its environment. The availablity of molecular sequence data
for nucleic acids and proteins had led to the development
of the genealogical species concept. Proponents utilize the
What Is a Species? distinct genetic history of organisms to differentiate species.
As indicated previously, each kind of organism is known Despite the lack of an all-inclusive botanical definition, the
as a species. Although this intuitive definition, based on concept of “species” facilitates the naming, describing, and
morphological similarities, works fairly well in many cir- classifying of plants in a uniform manner. An inventory of
cumstances, it is limited; scientists have given much thought the world’s species is the first step in preserving biodiver-
to the biological basis of a species. Many accept the biologi- sity, as discussed in A Closer Look 8.2—Saving Species
cal species concept first proposed by Ernst Mayr in 1942, through Systematics.



Table 8.4
Economically Important Angiosperm Families

Scientific Family Name Common Family Name Economic Importance
Aceraceae Maple Lumber (ash, maple), maple sugar
Apiaceae Carrot Edibles (carrot, celery), herbs (dill), poisonous (poison hemlock)
Arecaceae Palm Edibles (coconut), fiber oils and waxes, furniture (rattan)
Asteraceae Sunflower Edibles (lettuce), oils (sunflower oil), ornamentals (daisy)
Brassicaceae Mustard Edibles (cabbage, broccoli)
Cactaceae Cactus Ornamentals, psychoactive plants (peyote)
Cannabaceae Hemp Psychoactive (marijuana), fiber plants
Cucurbitaceae Gourd Edibles (melons, squashes)
Euphorbiaceae Spurge Rubber, medicinals (castor oil), edibles (cassava), ornamentals (poinsettia)
Fabaceae Bean Edibles (beans, peas), oil, dyes, forage, ornamentals
Fagaceae Beech Lumber (oak), dyes (tannins), ornamentals
Iridaceae Iris Ornamentals
Juglandaceae Walnut Lumber, edibles (walnut, pecan)
Lamiaceae Mint Aromatic herbs (sage, basil)
Lauraceae Laurel Aromatic oils (bay leaves), lumber
Liliaceae Lily Ornamentals, poisonous plants
Magnoliaceae Magnolia Ornamentals, lumber
Malvaceae Mallow Fiber (cotton), seed oil, edibles (okra), ornamentals
Musaceae Banana Edibles (bananas), fibers
Myrticaceae Myrtle Timber, medicinals (eucalyptus), spices (cloves)
Oleaceae Olive Lumber (ash), edible oil and fruits (olive)
Orchidaceae Orchid Ornamentals, spice (vanilla)
Papaveraceae Poppy Medicinal and psychoactive plants (opium poppy)
Piperaceae Pepper Black pepper, houseplants
Poaceae Grass Cereals, forage, ornamentals
Ranunculaceae Buttercup Ornamentals, medicinal and poisonous plants
Rosaceae Rose Fruits (apple, cherry), ornamentals (roses)
Rubiaceae Coffee Beverage (coffee), medicinals (quinine)
Rutaceae Citrus Edible fruits (orange, lemon)
Salicaceae Willow Ornamentals, furniture (wicker), medicines (aspirin)
Solanaceae Nightshade Edible (tomato, potato), psychoactive, poisonous (tobacco, mandrake)
Theaceae Tea Beverage (tea)
Vitaceae Grape Fruits (grapes), wine


A CLOSER LOOK 8.2
Saving Species through Systematics

Earth is blessed with a tremendous variety of living organ- plants and animals. Commercial fishing is in essence the
isms. About 1.4 million living microbes, fungi, plants, and hunting of wild fish populations. Blueberries and maple syrup
animals have been identified by systematics. The number of are just two examples of foods gleaned from nature in the
yet undescribed species is much greater, with estimates rang- United States. Wood and wood pulp are other products har-
ing between 10 million and 100 million. Biodiversity is an vested from biodiversity resources. Biodiversity in itself is a
inventory of the number and variety of organisms that inhabit major economic force, as evidenced by the increasing popu-
Earth. We are currently in the midst of a biodiversity crisis; larity of ecotourism. Sport fishing, hunting, and bird-watching
the variety of living species is declining owing to an acceler- are other examples of economically profitable activities that
ated extinction rate. Human activities are responsible for this depend on the preservation of biodiversity. Lastly, nearly half
terrible loss. Over 6.6 billion people at present inhabit Earth, of the medicinals now in use originated from a wild plant, and
and this number is expected to increase to over 9 billion in it has been estimated that between 35,000 and 70,000 spe-
the next 50 years. Population pressures cause natural areas cies of plants are used directly as medicines worldwide.
to be cleared for agriculture or expanding urbanization. More Knowledge of systematics has many practical applications.
people also results in more pollution that fouls the land, sea, There has been a movement to reduce our dependence
and air. All of these human-induced changes translate into a upon chemical pesticides and instead rely more heavily on
death toll upon the world’s biodiversity. biological controls to manage nuisance organisms. Biological
Consider the tropical rain forests of the world. These control methods depend upon proper identification of a pest,
forests are some of the most biologically diverse areas on the knowledge of its life cycle, and correct identification of its
planet, home to approximately 70% of the world’s species. predators and susceptibility to disease. Misidentification can
Unfortunately, these forests have been subjected to massive be costly. Mealybugs are noxious pests that can cause mas-
destruction. Scientists have calculated that species loss in the sive damage to crops. A species of mealybug was identified as
tropical rain forests is currently 1% to 5% per decade and will the culprit in the devastation of coffee plantations in Kenya.
increase to 2% to 8% by the year 2015. This rate translates Biological control methods were employed using the natural
to an average loss of 9,000 species per year, or a heartbreak- enemies of the identified species of mealybug but were inef-
ing 225,000 extinctions between 1990 and 2015. fective. Further investigation revealed that the mealybug had
Why should we care about biodiversity? Biodiversity been misidentified. Once the correct species was assigned,
is the basis for the necessary essentials to human existence: natural pests of the mealybug were brought in from its native
food, fiber, fuel, and shelter. Of the estimated more than habitat in Uganda, and the mealybug infestation was soon
250,000 species of angiosperms, nearly 20,000 have been brought under control. Knowledge of systematics can be
used at one time or another as food for humans. Advances in used to predict economic uses of little known but related
agriculture are dependent upon the interaction between sys- species. Researchers identified anticancer compounds from
tematics and biodiversity. Since the 1960s, world crop yields Kenyan populations of Maytenus buchananii. There was a
have increased two- to four-fold. Part of this increase is due problem, however; the species was rare in this locality.
to the creation of improved crop varieties through breeding Knowledge of systematics suggested that closely related spe-
programs and more recently through genetic engineering. cies would probably possess the same chemical compounds.
Locating and identifying relatives of crop species have been This proved to be the case when a population of the same
of critical importance to agricultural research in breeding for genus but different species was collected from India.
desirable characteristics. With the advent of genetic engi- Clearly, the preservation of biodiversity should be of
neering, nearly any plant species is a potential source of genes utmost importance to everyone. Systematic research is fun-
for transfer to agricultural crops. Ironically, the conversion damental to learning about the characteristics and dimensions
of native ecosystems to agricultural lands in an attempt to of biodiversity. Systematics is necessary to identify localities
accommodate the food demands of an exponentially grow- of high species diversity or rare species. Baseline data must
ing human population may eliminate the very organisms on be collected to ascertain which species are declining in num-
which agriculture depends for its future. Fertile soil, obvi- bers or those whose range is becoming limited. Knowledge
ously essential for the vitality of agricultural crops, is also a of systematics will determine if exotic pests are moving into
by-product of biodiversity because it is formed through the new areas and threatening native species. Without scientific
interactions of a number of soil organisms: fungi, earthworms, identification and mapping, valuable habitats and the species
bacteria, plant roots, and burrowing mammals. Species loss found there will be lost. In fact, Systematics Agenda 2000 is
could result in soils unable to support vegetation. an ongoing global initiative by the scientific community to dis-
Not all of the world’s supply of food comes from cul- cover, describe, and classify the world’s species in an effort
tivated sources. There is still a substantial harvest of wild to understand and conserve biodiversity.
133



Kingdom: Plantae Plant kingdom Figure 8.7 Major ranks in the taxonomic hierarchy. Note that
the higher the ranking, the broader the defining characteristics and
the more inclusive the group.

Table 8.5 Traditional and
Standardized Names for Some
Common Families

Family Traditional Standardized
Name Name Name
Division: Magnoliophyta Flowering plants Sunflower Compositae Asteraceae
Mustard Cruciferae Brassicaceae
Grass Gramineae Poaceae
Mint Labiatae Lamiaceae
Pea Leguminosae Fabaceae
Palm Palmae Arecaceae
Carrot Umbelliferae Apiaceae

Class: Liliopsida Monocots Table 8.6 The Taxonomic
Hierarchy and Standard Endings

Standard
Rank Ending Example
Division (Phylum) -phyta Magnoliophyta
Class -opsida Liliopsida
Order -ales Liliales
Family -aceae Liliaceae
Order: Liliales Genus Lilium
Species Lilium superbum L.

Family: Liliaceae Lily family THE INFLUENCE OF DARWIN’S
THEORY OF EVOLUTION
The theory of evolution by means of natural selection was to
irrevocably change the way biologists view species. Instead
of unchanging organisms and generations created all alike, it
Genus: Lilium Lilies was realized that species are dynamic and variable, continu-
ally evolving through the mechanism of natural selection in
which adaptions are refined to a changing environment.

The Voyage of the HMS Beagle
Species: Lilium Turk’s Cap Lily Charles Robert Darwin (fig. 8.8) was born in England in
superbum L. 1809 to a family of distinguished naturalists and physi-
cians. His grandfather was Erasmus Darwin, a well-known
poet and physician, and his father, Robert Darwin, was a
successful country doctor. At 15 years of age, Charles was
sent to the University of Edinburgh Medical School to study
medicine. Not finding it to his liking, he transferred after



2 years to Cambridge University to study theology. While at
Cambridge, he spent much of his free time with the students
and professors of natural history. This association later proved
invaluable. In 1831, at the age of 22, Darwin graduated from
Cambridge with a degree in theology. Shortly thereafter he
was recommended as ship naturalist by John Henslow, one of
the natural history professors at Cambridge. The ship in ques-
tion was the HMS Beagle, commissioned by King William
IV to undertake a voyage around the world for the purpose of
charting coastlines, particularly that of South America, for the
British navy. The voyage of the Beagle began on December
27, 1831, and was to last 5 years (fig. 8.9). During his time
on the Beagle, Darwin collected thousands of plants and other
specimens from South America, the Galápagos Islands (off
the coast of Ecuador), Australia, and New Zealand. He stud-
ied geological formations and noted fossil forms of extinct
species. He found that some fossils of extinct species bore a
striking resemblance to extant species, as though the former
had given rise to the latter. Darwin spent some time studying
the species found on the Galápagos Islands. He noted that
animals and plants found in the Galápagos were obviously
similar to species found in South America, but there were
distinct differences. These observations led Darwin to ques-
tion the fixity of species concept. According to this concept,
widely held at the time of Darwin, species were acts of Divine
Creation, unchanging over time.
When the Beagle returned to England in 1836, Darwin
Figure 8.8 Charles Darwin (1809–1882) published The Origin married his cousin Emma Wedgwood (of the famous
of Species in 1859.

British
Isles Europe
North Azores
America
Atlantic Asia
Ocean Canary
Islands Paciﬁc
Cape Verde Ocean
Islands Africa
Galápagos
Islands

Bahia
South
Tahiti America Cocos
Rio de Islands Australia
Janeiro Sydney
Valparaíso Montevideo
Cape of King George
Good Hope Sound New
Falkland Tasmania Zealand
Islands
Cape Horn

Figure 8.9 The 5-year voyage of the HMS Beagle. Darwin’s observations on the geology and distributions of plants and animals in
South America and the Galápagos Islands were the groundwork for the development of the theory of evolution by means of natural
selection.



Wedgwood china family) and settled, at age 27, in the English
countryside. He continued his work in natural history, con-
ducting experiments, writing papers, and corresponding with Concept Quiz
other naturalists. Among his works was a four-volume trea- Darwin identified four conditions that are necessary if evo-
tise on the classification and natural history of barnacles. lution is to occur: genetic variation, overproduction of off-
In 1842, he began putting his thoughts together on what spring, competition for limited resources, and reproduction
was to become his theory of evolution by natural selection. of the fittest.
Darwin continued to expand and fine-tune his thoughts over
Imagine a plant population that reproduces entirely by asexual
the next 16 years. In June of 1858, he received a manuscript
methods, such as spreading by underground stems. Although
from Alfred Russel Wallace (1823–1913), a young British
there are many individual plants in the population, they are
naturalist working in Malaysia. Wallace’s work was entitled
essentially a single plant genetically; that is, they are clones. Can
On the Tendency of Varieties to Depart Indefinitely from
natural selection act on a population of clones? Is this population
the Original Type; Wallace had independently arrived at
capable of evolving? Explain.
the concept of natural selection. Wallace and Darwin jointly
presented their ideas on July 1, 1858, at a meeting of the
Linnean Society in London. During the next few months,
Darwin completed writing what was to become one of the
most influential texts of all time. With the publication on
In addition to natural selection, humans have long used
November 24, 1859 of On the Origin of Species by Means of
artificial selection, natural selection as practiced by humans
Natural Selection, or the Preservation of Favoured Races in
(see Chapter 11), to shape the characteristics of crop plants to
the Struggle for Life by Charles Darwin, biological thought
suit the needs of humanity. The most serious flaw in Darwin’s
was changed forever.
Theory of Evolution was the mechanism of heredity. Darwin
had not worked out the source of variation in species, nor
Natural Selection did he understand the means by which traits are passed down
There are four underlying premises to Darwin’s theory of from generation to generation. It would take an Austrian
evolution by natural selection: monk, Gregor Mendel (see Chapter 7), working in relative
obscurity with pea plants, to come up with the answers to
1. Variation: Members within a species exhibit individual
Darwin’s questions about inheritance.
differences, and these differences are heritable.
A well-known example of natural selection is the case
2. Overproduction: Natural populations increase geometri- of heavy-metal tolerance in bent grass, Agrostis tenuis.
cally, producing more offspring than will survive. Certain populations of bent grass were found growing near
3. Competition: Individuals compete for limited resources, the tailings, or soil heaps, excavated from lead mines in
what Darwin called “a struggle for existence.” Wales despite the fact that mine soils had high concentra-
4. Survival to reproduce: Only those individuals that are tions of lead and other heavy metals (copper, zinc, and
better suited to the environment survive and reproduce nickel). When mine plants were transplanted into uncon-
(survival of the fittest), passing on to a proportion of their taminated pasture soil, all survived but were small and
offspring the advantageous characteristics. slow growing. A nearby population of bent grass from
uncontaminated pasture soil exhibited no such tolerance
Offspring that inherit the advantageous traits are selected
when transplanted into mine soil; in fact, most (57 out of
for survival and many will live to reproductive age passing on
60) of the pasture plants died in the lead-contaminated
the desirable attributes. Those that do not inherit these traits
soil. The survival of the three pasture plants in mine soil is
are not likely to survive or reproduce. Gradually, the species
significant; undoubtedly these three possessed an advanta-
evolves, or changes, as more and more individuals carry these
geous trait, the ability to tolerate heavy-metal soil. A trait
traits. Darwin gave this example:
that promotes the survival and reproductive success of an
If the number of individuals of a species with plumed organism in a particular environment is an adaptation. The
seeds could be increased by greater powers of dis- mine plants had descended from bent grass plants that pos-
semination within its own area (that is, if the checks sessed the adaptation that conferred tolerance to the mine
to increase fell chiefly on the seeds), those seeds soil; over time (less than 100 years in this case) populations
which were provided with ever so little more down, of Agrostis tolerant to heavy metal evolved from those few
would in the long run be most disseminated; hence tolerant individuals.
a greater number of seeds thus formed would ger- Although Darwin’s theory of natural selection is the
minate, and would tend to produce plants inheriting foundation of modern evolutionary concepts, biologists today
the slightly better-adapted down. are still learning about the forces that shape evolution.



indicates that the traditional dicots represent several evolution-
ary lineages. Most of the dicots do comprise a clade and are now
Concept Quiz called the eudicots or true dicots. Approximately 75% of all
Natural selection favors the survivorship of those individu- angiosperm species are now classified as eudicots. Traditional
als in a population that possess characteristics crucial for dicots excluded from the clade eudicot are called the paleodi-
survival. cots (literally old dicots) by some authorities and include sev-
eral ancient lineages in the evolution of angiosperms.
You observe that trees in a part of a forest in which deer are
plentiful have higher branches than the trees in a fenced-off part
of the forest. Explain the different selective forces at work in CHAPTER SUMMARY
these two different environments.
1. Plant systematics has its origins in the classical works of
Theophrastus of ancient Greece, who is generally regarded
as the Father of Botany. The study of plants, as did many
other intellectual endeavors, went into a decline during
PHYLOCODE the Dark Ages of Europe but was later revived owing to
renewed interest in herbalism during the fifteenth to sev-
The Linnaean system of nomenclature and the hierarchy of enteenth centuries.
classification that has been presented in this chapter were
created more than 250 years ago, before Charles Darwin and 2. Linnaeus, a Swedish botanist of the eighteenth century,
Alfred R. Wallace had proposed their evolutionary theory is credited with the creation of the binomial, or scientific
by means of natural selection. Linnaean nomenclature is an name. Although common names are often informative and
artificial system based upon the appearance of organisms readily accessible, scientific names have the advantage of
that often does not reflect their evolutionary relationships, or being recognized the world over and unique to a single
phylogeny. Currently, there is a movement to reject this pre- species.
evolutionary taxonomy and replace it with a new system of 3. The taxonomic hierarchy includes the major ranks:
nomenclature, called PhyloCode, that is truly phylogenetic. domain, kingdom, division (phylum), class, order, family,
PhyloCode is based upon the work of the twentieth- genus, and species.
century German entomologist Willi Hennig, who proposed 4. Biologists have wrestled with the concept of the species;
that only shared derived characteristics should be used to the biological concept describes a species as a group of
define a group of related organisms. He further proposed that interbreeding populations, reproductively isolated from
each group constructed should be monophyletic, or composed other populations.
of only those organisms that can trace their descent from a 5. Charles Darwin and his theory of evolution by natural
common ancestor. These natural groupings are known as selection irrevocably changed the way biologists viewed
clades. species. Natural selection favors those individuals that
First introduced in 1983, the PhyloCode abandons the possess traits that better enable them to survive in the
Linnaean ranks of the taxonomic hierarchy. In this system, environment. These individuals survive to reproduce, and
as new information that may change a group’s ranking accu- many of their offspring will tend to have these adaptations
mulates, names are not changed, as they would be with the and pass them on to future generations. In this way, popu-
Linnaean system, which associates different suffixes with lations change over time. The four underlying conditions
different ranks. Instead of ranks, clades are the only groups of Darwin’s theory of evolution by natural selection are
recognized. Opponents fear that a complete abandonment of variation, overproduction of offspring, competition, and
all ranks will result in a loss of comparative information and survival to reproduce.
encourage a proliferation of names that, without any context,
will serve only to confuse the nomenclature.
Released in 1991, the APG (American Phylogeny Group) REVIEW QUESTIONS
system compared the sequence data of select genes to clas-
1. List the common names of some of the wildflowers in
sify the flowering plants. The highest formal rank in this
your area. Determine the type of information each name
classification system is the order; higher categories are only
imparts.
identified as clades. As more data accumulated, APG II, an
update of the classification, became available in 2003. In this 2. Using a plant dictionary (see Further Reading) look up the
system, angiosperms are recognized as a clade, sharing several scientific names and their meanings for common house-
distinct characteristics, such as ovules enclosed in a carpel plants and landscape plants in your area.
and double fertilization. Within the angiosperms, all mono- 3. Briefly describe the concept of evolution by natural
cots appear to belong to a distinct clade, but molecular data selection.



4. Why are only inherited traits important in the evolution- Laufer, Geraldine Adamich. 1996. Tussie-Mussies. The Herb
ary process? Companion April/May: 48–53.
5. How do mutations (Chapter 7) lead to the evolution of Litt, Amy. 2006. Origins of Floral Diversity. Natural History
new species? 115(5): 34 –40.
6. What was the lasting contribution of Linnaeus? How was Mayr, Ernst. 2000. Darwin’s Influence on Modern Thought.
the binomial system an improvement over polynomials? Scientific American 283(1): 78–83.
7. In what ways can systematics preserve biodiversity? Miller, Douglass R., and Amy Y. Rossman. 1995. Systematics,
Biodiversity, and Agriculture. BioScience 45(10): 680–
FURTHER READING 686.
Blunt, Wilfrid. 1971. The Compleat Naturalist: A Life of Pennisi, Elizabeth. 2001. Linnaeus’s Last Stand? Science
Linnaeus. The Viking Press, New York, NY. 291: 2304–2307.
Briggs, David, and S. Max Walters. 1984. Plant Variation Piementel, David, Christa Wilson, Christine McCullum,
and Evolution, 2nd Edition. Cambridge University Press, Rachel Huang, Paulette Dwen, Jessica Flack, Quynh Tran,
Cambridge, MA. Tamara Saltman, and Barabara Cluff. 1995. Economic
Coombes, Allen J. 1994. Dictionary of Plant Names: Botanical and Environmental Benefits of Biodiversity. BioScience
Names and Their Common Equivalents. Timber Press, 47(11): 747–757.
Beaverton, OR. Quammen, David. 2004. Darwin’s Big Idea. National
Conniff, Richard. 2006/2007. Happy Birthday Linnaeus. Geographic 206(5): 2–35.
Natural History 115(10): 42–47. Quammen, David. 2007. The Name Giver. National
Darwin, Charles (author) and Edward O Wilson (editor) 2006. Geographic 211(6): 72–87.
From So Simple A Beginning: The Four Great Books of Raby, Peter. 2001. Alfred Russel Wallace: A Life. Princeton
Charles Darwin. W. W. Norton & Company, New York. University Press, Princeton, NJ.
Friedman, William E. 2006. Sex Among the Flowers. Natural Savage, Jay M. 1995. Systematics and the Biodiversity Crisis.
History 115(9): 48–53. BioScience 45(10): 673–679.
Gilbert, Bil. 1984. The Obscure Fame of Carl Linnaeus. Schiebinger, Londa. 1996. The Loves of Plants. Scientific
Audubon 86:102–115. American 274(2): 110–115.
Greenaway, Kate. 1992. Language of Flowers. Dover Press, Sulloway, Frank J. 2005. The Evolution of Charles Darwin.
New York, NY. Smithsonian 36(9): 58–69.
Irvine, William. 1983. Apes, Angels, and Victorians: The Withgott, Jay. 2000. Is It “So Long, Linnaeus?” BioScience
Story of Darwin, Huxley, and Evolution. University Press 50(8): 646–651.
of America, New York, NY.
Judd, Walter S., Christopher S. Campbell, Elizabeth A.
Kellogg, Peter F. Stevens, and Michael J. Donoghue.
2002. Plant Systematics, A Phylogenetic Approach, 2nd ONLINE LEARNING CENTER
Edition. Sinauer Associates, Sunderland, MA.
Kohn, David. 2005. The Miraculous Season: The Historical Visit www.mhhe.com/levetin5e for online quizzing, web links
to chapter-related material, and more!
Darwin. Natural History 114(9): 38–40.
Laufer, Geraldine Adamich. 1993. The Language of Flowers.
Workman Publishing, New York, NY.

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