If you were given an unknown plant and asked to determine whether it is a conifer or a cycad, what would you look for if given only wood? Only leaves? If you were given an unknown plant and asked to determine whether it is a conifer or a cycad, what would you look for if given only wood? Only leaves? Solution CONIFERS IDENTIFICATION STEM (OR) WOOD Stems raise the photosynthetic leaves into the light and provide a channel for nutrients between the leaves and the roots. Most of the diameter of mature conifer stems consists of secondary xylem (wood) produced by the vascular cambium, a permanent cylinder of dividing cells that lies just inside the bark. Because the growth of most conifers is cyclic, the wood generally consists of distinct growth rings, which are delimited by the juxtaposition of small dark cells from the end of a growing season with larger, lighter cells that mark resumption of growth. In temperate conifers, the rings correspond to annual growth flushes, since no wood is formed during winter dormancy. Tropical species may lack this correspondence unless their habitat has strong seasonal variation in rainfall. Otherwise, they may have more than one growth ring in a year, each accompanying a new flush of leaves and branches. The wood of conifers is generally more uniform and simpler in structure than that of flowering plants. One type of cell, the tracheid, serves both to transport water and to support the trunk so that conifers lack the more textured wood associated with the mixture of vessel elements and fibres in hardwoods. The wood may have longitudinal resin canals lined with living cells, but most of its living cells are found in the rays that extend horizontally from the centre of the stem to the vascular cambium. The pits, the tiny thinnings that connect adjacent wood cells, are quite varied among conifer families and genera and are one of the chief features used to identify conifer woods.The bark that clothes the trunks may be thin, smooth, and flaky, peeling annually to reveal fresh bright colours, as in the lacebark pine (Pinus bungeana) of China and the tecate cypress (Cupressus guadalupensis) of southern California and Baja California, or it may accumulate in broad, colourful plates, as in the ponderosa pine (Pinus ponderosa) of western North America, or as thick, fireproof, fibrous ridges on the giant sequoias (Sequoiadendron giganteum). The practiced eye can distinguish different species of co-occurring conifers by their bark alone.Some conifers have transient special determinate twigs called short shoots that carry most of the photosynthetic leaves. In the bald cypress (Taxodium) and dawn redwood (Metasequoia), the short shoots look like double-sided combs and are shed each fall, to be followed by new ones in the same spots on the branches when growth resumes the following spring. The short shoots of pine (Pinus), with their fascicles of two to five (rarely one or eight) needles, are retained for up to 20 years but .

1. If you were given an unknown plant and asked to determine whether it is a conifer or a cycad,
what would you look for if given only wood? Only leaves?
If you were given an unknown plant and asked to determine whether it is a conifer or a cycad,
what would you look for if given only wood? Only leaves?
Solution
CONIFERS IDENTIFICATION
STEM (OR) WOOD
Stems raise the photosynthetic leaves into the light and provide a channel for nutrients between
the leaves and the roots. Most of the diameter of mature conifer stems consists of secondary
xylem (wood) produced by the vascular cambium, a permanent cylinder of dividing cells that lies
just inside the bark. Because the growth of most conifers is cyclic, the wood generally consists of
distinct growth rings, which are delimited by the juxtaposition of small dark cells from the end of
a growing season with larger, lighter cells that mark resumption of growth. In temperate conifers,
the rings correspond to annual growth flushes, since no wood is formed during winter dormancy.
Tropical species may lack this correspondence unless their habitat has strong seasonal variation
in rainfall. Otherwise, they may have more than one growth ring in a year, each accompanying a
new flush of leaves and branches.
The wood of conifers is generally more uniform and simpler in structure than that of flowering
plants. One type of cell, the tracheid, serves both to transport water and to support the trunk so
that conifers lack the more textured wood associated with the mixture of vessel elements and
fibres in hardwoods. The wood may have longitudinal resin canals lined with living cells, but
most of its living cells are found in the rays that extend horizontally from the centre of the stem
to the vascular cambium. The pits, the tiny thinnings that connect adjacent wood cells, are quite
varied among conifer families and genera and are one of the chief features used to identify
conifer woods.The bark that clothes the trunks may be thin, smooth, and flaky, peeling annually
to reveal fresh bright colours, as in the lacebark pine (Pinus bungeana) of China and the tecate
cypress (Cupressus guadalupensis) of southern California and Baja California, or it may
accumulate in broad, colourful plates, as in the ponderosa pine (Pinus ponderosa) of western
North America, or as thick, fireproof, fibrous ridges on the giant sequoias (Sequoiadendron
giganteum). The practiced eye can distinguish different species of co-occurring conifers by their
bark alone.Some conifers have transient special determinate twigs called short shoots that carry
most of the photosynthetic leaves. In the bald cypress (Taxodium) and dawn redwood

2. (Metasequoia), the short shoots look like double-sided combs and are shed each fall, to be
followed by new ones in the same spots on the branches when growth resumes the following
spring. The short shoots of pine (Pinus), with their fascicles of two to five (rarely one or eight)
needles, are retained for up to 20 years but are finally shed and almost never grow out as
branches. In contrast, the peglike short shoots of larch (Larix) and true cedar (Cedrus), like those
of Ginkgo, are permanent, elongating slowly and producing new needles each year. The flattened
sprays of branchlets of cedars in the family Cupressaceae may act like short shoots, falling intact
after a relatively brief life, or they may provide the framework for further branching.
LEAVES
Leaves are specialized photosynthetic organs. The varied leaves of conifers are attached singly
along the stems in a helical pattern (in some genera the leaves appear whorled) or in opposite
pairs or trios. Many Cupressaceae and a few other conifers have minute scale leaves only a few
millimetres long. Diverse needle- and claw-shaped leaves range in length from about 1 cm in
many conifers to more than 30 cm (12 inches) in some species of pine. Broad flat oblong blades
up to 30 cm long occur in Agathis and some species of Decussocarpus from East Asia, and the
monkey puzzle tree (Araucaria araucana) of Chile has hefty triangular wedges. The notched
needles of the Japanese umbrella pine (Sciadopitys verticillata) are the oddest leaves among
living conifers. They can be needlelike phylloclades or a pair of longitudinally fused needles.
The largest conifer leaves were those of the extinct genus Cordaites, with great paddle- or strap-
shaped leaves up to 1 metre (3 feet) long and 15 cm (6 inches) wide.
Most conifer leaves, whatever their shape, minimize water loss. The reduced surface area of the
scale- to needle-shaped leaves is an obvious example, but even the broader forms often have a
thick, waxy coating that makes them waterproof. The gas-exchange openings of the leaves
(stomates) are usually confined to a pair of narrow bands on the under surface and are deeply
sunken into chambers that separate them from direct contact with the dry air surrounding the
leaf.
CYCADS IDENTIFICATION
STEM
Stems of cycads are characteristically short and stout, and while most genera have some species
with subterranean, tuber like stems, a majority of species are arborescent. The taller cycads
include Microcycas calocoma (up to 10 metres high), Macrozamia moorei (up to 18 metres),
Dioon spinulosum (up to 16 metres), Lepidozamia hopei (up to 18 metres), and Encephalartos
altensteinii (up to 20 metres), but most of the arborescent (treelike) species have trunks only two
to three metres high. The stems of most arborescent species are covered with an armour
composed of the hardened leaf and cataphyll bases, but internally they are rather soft and fleshy,
with a thick parenchymatous cortex, a large pith, and scanty woody tissue. In most cycads, the

3. woody tissue is on the order of five to 10 millimetres wide, but Dioon spinulosum has an
exceptional amount of wood, in some specimens up to 10 centimetres wide. This may constitute
evidence of the primitive nature of the genus, because seed ferns also generally had stems with
considerably more wood than those of most living cycads. Even in Dioon, there is no evidence of
annual growth rings, so that age estimates must rely on other evidence, most often on counts of
the whorls of leaf scars, which can be related to annual or biennial production of new leaf
flushes. On this basis, it has been estimated that some cycads (notably Dioon and Macrozamia)
may be as much as 1,000 years old; however, it is doubtful that most cycads are that old.
Species of Macrozamia, Encephalartos, and Cycas often develop additional cylinders of vascular
tissue, apparently formed from vascular cambia originating in the cortex. The result is a
condition in which concentric rings of xylem and phloem are present, often two or three, but in
exceptional cases, as many as 14. The xylem of cycad seedlings and that of some subterranean
stems (Stangeria, Zamia) is composed of scalariform tracheids; in older stems, the tracheids
exhibit primitive, multiseriate, bordered pits.
Another feature of those cycad stems in which terminal cones are produced is the presence of
“cone domes” in the pith. In longitudinal sections, the pith appears partitioned horizontally at
intervals by vascular tissue. Each cone dome represents the displacement of a cone axis to one
side as a result of the initiation and growth of the new vegetative apex.
The cycad stem grows from the tip (apically); the only lateral buds and branches are those
unusually placed (adventitious) stems, whose buds arise by regeneration after the apical growth
tissue (meristem) has been destroyed or as a result of wounding. Apical dominance and lack of
branching bring about an apparent single-stemmed (monopodial) growth form, so that older
plants become quite palmlike. This appearance, however, is deceptive, because in more than half
the genera the apical meristem is converted from a vegetative to a reproductive function in that it
is transformed into a strobilus (cone). A new vegetative meristem arises to one side of the cone
meristem; subsequent growth and enlargement further displace the cone or cones to the side, so
that the monopodial appearance is maintained even though the type of growth is actually
sympodial. Only members of three genera (Macrozamia, Lepidozamia, Encephalartos) have
cones initiated to the side and are truly monopodial; the remaining eight are considered
sympodial.
Cycads have such thick stems that rearrangements of internal vascular connectives are not
externally apparent. The cycad trunk is about as thick at its crown as at its base, thus furthering
the resemblance to palms. Such stems, termed pachycaulous, result as in palms from activity of a
primary thickening meristem (PTM) lateral to the apical meristem, which produces much greater
increments of cortical parenchyma than would result if only an apical meristem were present.
This is an important difference between cycadophytes and coniferophytes, for in the latter there

4. is no PTM and the stem at its apical end is relatively smaller than at its base.
LEAVES
The leaves of cycads are for the most part once-pinnately compound; however, in the genus
Bowenia, the leaves are bipinnate and quite fern like. Stangeria also has fern like leaves, and
before cones were found to be associated with them the plant was described as a fern in the
genus Lomaria. Stangeria leaves and those of the recently described Chigua are unique in
possessing pinnately veined leaflets with midribs and side veins. Cycas pinnae also have midribs,
but these lack side veins altogether. Pinnae of all other cycads have dichotomously branching,
more or less parallel veins. The size of the cycad leaf is variable; Zamia pygmaea, the smallest
cycad, has leaves about 20–30 centimetres long, while some species of Macrozamia,
Lepidozamia, Ceratozamia, and Cycas have leaves three metres in length.
In cross section, the pinnae of most cycads are rather thick and sclerophyllous. The stomata are
sunken and are of the type known as haplocheilic; that is, the guard cells arise directly from the
mother cell, as contrasted with the syndetocheilic type, in which the guard cells are one division
removed from the mother cell. The haplocheilic type is found in living conifers, pteridosperms,
cycads, Ginkgo, and some others but not in the Cycadeoidea.Bushing between cycad and
cycadeoid fossils.