The document discusses ecological adaptations of plants in response to environmental changes, focusing on xeric, hydric, and mesic conditions. It details the types of aquatic (hydrophytes) and terrestrial (xerophytes) plants, their structural, physiological, and behavioral adaptations to varying water availability, and how these adaptations have evolved over time. Key adaptations include root, stem, and leaf modifications that enhance survival in respective environments.

1. B.Sc. I, Sem. II, Paper III
PLANT ECOLOGY
Associate Professor, Dr. S. A. Gaikwad
Dept. of Botany
Vidnyan Mahavidyalaya, Sangola

2. Ecological adaptation
Adaptations in an organism or in the community are generally for the changes in the entire
environment. The organisms adapt to the changes in the surrounding atmosphere because of the
basic property of the protoplasm, known as the adaptability. The adaptability helps the organisms
to remain in the process of evolution. The ecological adaptations are the responses shown by the
plants to the environmental conditions and they are the adjustments as per environmental changes.
“The changes in the characters, which enable the organisms to withstand the changes in the
surrounding environment and to make use of these changes for the maximum benefits, are
known as adaptations.”
The adaptations which are induced by water factor or availability of water in the environment are
of three types – xeric, hydric and mesic. These terms are used for the environmental conditions
which are responsible for respective adaptations.

3. Ecological adaptation
All adaptations may be structural, physiological or behavioral, are the result of evolution, which is a
change in a species over thousands of years or within a few lifetimes. The life cycle of any organism
is controlled by number of environmental factors. Water is the most essential factor for every living
organism. Plants growing under different environmental conditions exhibit various adaptation. For the
first time, Warming (1895) had realized the impact of different factors upon the vegetation in ecology
and he classified plants on the basis of nature of substratum on which they grow. Later on, Warming
(1909) classified the plants on the basis of their water requirements. The plants are divided into three
major groups as per their water requirements- 1. Hydrophytes- Plants growing in abundant water i.e.,
in maximum water supply and near the water, 2. Xerophytes- Plants growing in dry, arid region
which shows shortage of water in the soil i.e., in minimum supply of water, 3. Mesophytes- Plants
growing in habitat with neither less nor more water is available i.e., moderate water supply is
required.

4. Ecological adaptation - Hydric adaptation
Plants are either growing on land or in water. The land plants get essential water from the soil but the
aquatic plants are growing within or near the water. On the basis of availability of water, the adaptations
are of three types – Xeric, Hydric and Mesic.
A. Hydric Adaptations:
1. Water availability is far more than the requirement of plants.
2. There is no need of mechanical strengthening as plants are supported by water all around them.
3. Aquatic plants can only grow partially or completely in water or in soil that is permanently saturated
with water.
4. The habitat of aquatic plants is either fresh water or marine.
5. Underwater leaves and stems are flexible to move with water currents.
As the plants are growing in hydric conditions these are known as hydrophytes (Hydro- water, phytes -
plants). There are three different types of hydrophytes -

5. Ecological adaptation- Hydric adaptation
As the plants are growing in hydric conditions these are known as hydrophytes (Hydro- water,
phytes -plants). There are three different types of hydrophytes -
a. Submerged hydrophytes- Plants are b. Floating hydrophytes – These are of two types
growing under the water surface 1.Free floating hydrophytes: Freely floats on the water
e.g., Hydrilla, Potamogeton, Utricularia surface, not rooted in the soil e.g., Eichhornia, Pistia.

6. Ecological adaptation- Hydric adaptation
2. Floating but rooted hydrophytes: Plants are
rooted in the soil but leaves are floating on the
surface of water e.g. Nymphaea, Marsilea.
c. Amphibious hydrophytes - These are growing
in shallow water or in muddy soil i.e., in marshy
places e.g. Cyperus, Typha
All these hydrophytes have certain morphological, anatomical and physiological modifications
while growing in above aquatic conditions. These modifications are known as hydrophytic
adaptations which are discussed below-

7. Ecological adaptation- Hydric adaptation

8. Ecological adaptation- Hydric adaptation
• Roots: Root system of hydrophytes is not of much
importance, because they grow partially or
completely in water.
• Roots are poorly developed (e.g., Hydrilla,
Vallisneria.), reduced or completely absent (e.g.,
Utricularia, Ceratophyllum,).
• However, some hydrophytes have well developed
adventitious roots (e.g., Eichhornia, Pistia).
• Root caps usually absent. Root hairs are poorly
developed in most hydrophytes.
• Root tips are often provided with root pockets (e.g.,
Eichhornia).
Stem: In submerged hydrophytes, the stem is long,
slender thin, spongy and flexible e.g., Hydrilla.
• In free floating hydrophytes, the stem or stolon is
horizontal, spongy, thick and short, floating on the
surface of water e.g., Eichhornia, Azolla, Pistia
• while in rooted hydrophytes like Nymphaea,
Nelumbium, Cyperus, the stem is a rhizome. These
rhizomes live for many years and produce leaves
every year.
• Mucilaginous or waxy coating is present on entire
plant body.
Morphological(External)adaptations of Hydrophytes:

9. Ecological adaptation- Hydric adaptation
Morphological adaptations of Hydrophytes:
Petioles:
• Some floating hydrophytes show special
features in the petioles.
• In free floating but rooted hydrophytes
like Nymphaea and Nelumbium, petioles
are long, slender and spongy
• while they are swollen, spongy in free
floating hydrophyte like Eichhornia,
helps in floating.
Leaves:
• The leaves are thin, long or ribbon like (e.g.,
Vallisnaria). linear (e.g., Potamogaton) or finally
dissected (e.g., Ceratophyllum).
• The leaves may be long, flat, and entire as in
Nelumbo, Nymphaea.
• The petioles are long swollen and spongy (e.g.,
Eichhornia, Trapa).
• Heterophylly is observed in some plants.
Generally, the leaves are reduced in thickness and
covered by waxy coating.

10. Anatomical (Internal) adaptations of Hydrophytes: Leaves:
Root:
 Cuticle is very thin or absent.
 Root hairs present in amphibious hydrophytes.
 Epidermis is single layered made up of thin-
walled cells. Parenchymatous cortex i.e.,
arenchyma is well developed. It has numerous
air chambers which help in buoyancy
(floating) and rapid gaseous exchange.
 Conducting tissues, i.e., xylem and phloem,
developed poorly and less differentiated. Only
xylem tracheids are present in submerged
forms while phloem is well differentiated in
amphibious hydrophytes.
 Mechanical tissues are generally absent. Pith
is absent.
 Cuticle is absent or poorly developed in Nymphaea leaves.
 Epidermis is single layered with thin walled parenchymatous cells.
 Chlorophyll found in all the tissues. Epidermal cells of leaves contain
abundant chloroplasts and they can function as photosynthetic tissue,
especially where the leaves and stems are very thin e.g., Hydrilla.
 Stomata are totally absent in submerged plants, but in floating leaves,
stomata are present on the upper surface. In amphibious plants stomata
may be scattered on all the aerial parts.
 In submerged plants, mesophyll tissues are not differentiated while in
other forms of hydrophytes these are well differentiated into spongy
parenchyma and palisade tissues. They show air cavities.
 In submerged leaves, air chambers are filled with respiratory and other
gases.
 Mucilage canals and mucilage cells are present which secrete mucilage to
protect the plant body. Mechanical tissues are poorly developed or
completely absent.

11. Ecological adaptation- Hydric adaptation
Anatomical (Internal) adaptations of Hydrophytes:
Stem:
 Cuticle is very thin, poorly developed or absent.
 Epidermis is single layered with thin walled parenchymatous cells.
 The rhizome of Nymphaea and stem of Typha shows well developed
epidermis.
 In floating forms, thin walled parenchymatous or collenchymatous
hypodermis is present which is containing chloroplasts.
 Parenchymatous cortex is well developed with number of air chambers
which help in buoyancy (floating) and rapid gaseous exchange.
 Endodermis and pericycle is generally distinct.
 The vascular tissues, i.e., xylem and phloem, developed poorly, thin
walled except in amphibious hydrophytes.
 Mechanical tissues are poorly developed or absent.

12. Ecological adaptation- Hydric adaptation
Physiological Adaptations of Hydrophytes:
 Osmotic concentrations of cell sap are low.
 Entire plant surface absorbs water and nutrients.
 Hydrophytes maintain active photosynthesis as chloroplasts are
distributed throughout the plant body.
 CO2 and O2 evolved during respiration and photosynthesis is stored in
air chambers for future use.
 No transpiration from submerged plants.

13. Ecological adaptation- Xeric adaptation
As the plants are growing in xeric conditions these are known as xerophytes.
There are three different types of xerophytes -
a. Drought escaping plants (Ephemerals) - These are also called as drought
evaders which have a very short life cycle i.e., they are annuals, to avoid the
drought e.g. Tribulus terrestris, Argemone mexicana, Cassia tora etc.
b. Drought tolerant/enduring plants (succulents) - They store large
amount of water in different organs of their body, so they become
fleshy. They are called succulents. The stem succulents store water
in stem so it becomes fleshy, green and photosynthetic leaves are
reduced to spines e. g. Opuntia. In leaf succulents store water in
leaves and they become thick
fleshy as in Aloe, Portulaca.
1. Water availability in the soil is very low
than the requirement of plants.
2. The temperature is very high so
humidity is less which results in the loss
of water.
3. Arid, dry area with low rainfall,
4. Hot, dry climate is responsible for
increasing evaporation and transpiration.
5. All these environmental conditions are
responsible for drought in that habitat

14. Ecological adaptation- Xeric adaptation
c. Drought resisting plants (Non- succulents) - These
plants are the true xerophytes. They resist the drought
by showing external and internal adaptations to dry
conditions. Examples are Calotropis, Casuarina,
Nerium, Acacia.

15. Ecological adaptation- Xeric adaptation
Stem:
• The stem is hard, woody either aerial or subterranean, sometimes
covered with wax e.g., Equisetum.
• Stem may be covered with dense hairs as in Calotropis or thorns. In
some succulents, it is bulbous and fleshy.
• The extreme xerophytes like Opuntia, stem is modified into leaf like,
flattened fleshy structure known as phylloclade while in Asparagus it
is modified into small needle-like green structures exactly looking like
leaves called as cladodes. Both phylloclade and cladodes perform the
function of leaf i.e., photosynthesis.
Morphological adaptations of xerophytes:
Root:
• Root system is well developed and
profusely branched.
• The roots of perennial xerophytes
grow deep into the ground that can
penetrate several meters down where
plenty of water is available.
• Most of the desert plants like Cacti
develop superficial and shallow root
system which is able to absorb water
that is available near the surface of the
earth.

16. Morphological adaptations of xerophytes: Ecological adaptation- Xeric adaptation
Leaves:
• Leaves are thick and leathery, tough, shining (Nerium)
or may be thick, fleshy & succulent (Aloe).
• In some plants like Cacti, leaves are reduced, usually
small and fall off during prolonged dry conditions to
prevent water loss by simply losing their leaves,
absent or modified into spines (Zizyphus, Capparis,
Acacia).
• Leaf lamina may be long, narrow needle like as in
Pinus or divided into many leaflets like Acacia, leaf
apex & margin is spiny (Aloe).
• Curled leaves are present in some extreme xerophytic
grasses. The rolling or folding of leaves minimizing
the evaporation and water loss.

17. Ecological adaptation- Xeric adaptation
a) Succulent Xerophyte- Aloe b) Non succulent
xerophyte- Ziziphus

18. Anatomical adaptations of xerophytes: Ecological adaptation- Xeric adaptation
Roots:
 Root cap is present. Root hairs are
large in number.
 Conducting tissues, i.e., xylem
and phloem, developed very well.
 Thick cuticle is present which
protects internal tissues from dry
and hot soils.
Stem:
 Epidermis is thick walled and lignified.
 Some plants show wax deposition on the surface of
epidermis and even in the hypodermis.
 In succulent stems, thin walled parenchymatous
cells store excess amount of water, mucilage, latex,
etc. called water storage tissues.
 Woody xerophytes produce very well-developed
cork in the stem.
 Mechanical tissues and vascular tissues are well
developed.

19. Anatomical adaptations of xerophytes: Ecological adaptation- Xeric adaptation
Leaves:
 Epidermis with thick cuticle & epidermal cells are
thick walled.
 Multilayered epidermis is present on both upper and
lower surface of leaves.
 Sunken stomata are present and stomatal opening is
covered with number of hairs, presence of many
layered palisade tissue.
 Mesophyll is very compact with reduced intercellular
spaces.
 In succulent leaves, spongy parenchyma i.e., water
storage tissue stores water.
 Thick-walled sclerenchyma cells are seen in the
hypodermis e.g., Pinus needle.
 Well-developed vascular and mechanical tissues are
present.

20. Ecological adaptation- Xeric adaptation
Physiological Adaptations of Xerophytes:
 The stomata of these plants open during night hours and remain closed during the day to
prevent water loss by reducing evaporation rate.
 The xerophytes have very high osmotic pressure of the cell sap, which increases the turgidity of
the cell sap.
 These plants control the excessive loss of water during transpiration by reducing total
transpiring surface,
 Xerophytes have greater potentiality to resist wilting.
 The protoplasm in these plants is less viscous and more permeable and resistant to heat.
 These plants may secrete resins and waxes (epicuticular wax) on their surfaces, which reduce
evaporation.