Animal and Plant xerophytic Adaptation

1. Xerophytes
Dr. Asmita Daspute.
Assistant Professor,
SBES College of Science, Aurangabad.

2. XEROPHYTES
• A xerophyte (gr. Xeros, dry; phyton, plant) is a plant which is able to survive in an
Environment with low availability of water or moisture, such as desert, ice or snow covered
Region.
• Xerophytes defined as "plants of dry habitats".
• Xerophytes are plants adopted in order to survive or grow in dry habitats (xeric condition)
• Where the availability of water is very less.
• Xerophytes are plants of relatively dry habitats - dry in soil and most often also climatically.
• Xerophytes plants live in condition of water scarcity i.E. In xeric condition (habitat). Xeric
Habitats are of two types -

3. Xeric habitats are of two types -
 1) Physically dry habitat :- Water retaining capacity of the soil very low and climate is
 dry. Water cannot retained like desert or rock surface.
 2) Physiologically dry :- Water is present in excess, but not in absorbable conditions or
 the plants cannot absorb it. e.g. high salt water, high acidic water and high cold water,
 water in snow form.

4. Adaptation Strategies of Xerophytes :-
 Xerophytes adopt various features according to
 their climate, geography and requirements. Xerophytes plants aim at the following adaptation
 strategies :-
 1) Absorb more water from the surrounding.
 2) Retain water in their organs.
 3) Reduce the water loss by transpiration to minimise.
 4) Reduce utilisation of water ( Prevent high consumption of water)

5. Types Of Xerophytes
 1) Ephemeral Annuals ( Drought Evaders or Drought Escapers)
 * They are also called as 'drought evaders' or 'drought escapers' common in arid zones.
 * They are annuals, which complete their life cycles within a very short period.
 * They actually avoid and not withstand dry seasons, and thus escape dryness in
 external and internal environments.
 * They survive critical dry periods as seeds or propagules. With the onset of rainfall,
 the plant seeds germinate, quickly grow to maturity, flower, and set seed, i.e., the
 entire life cycle is completed before the soil dries out again.
 * They are usually shorts sized plants in which the flowering and fruiting occur before
 the next unfavourable season.
 * The principal morphological adaptation of ephemeral are their small size and large
 shoot in relation to root system.
 * Most of these plants are small, roundish, dense shrubs represented by species of
 Papilionaceae, some inconspicuous Compositae, and some grasses
 * Examples - Solanum xanthocarpum, Argemone mexicana, Cassia tora etc.

7. 2) Succulents Xerophytes ( Drought Enduring Xerophytes) -
 * These plants suffer from dryness in their external environment only. Their
 succulent, fleshy organs (stems, leaves, roots) serve as water storage organs
 which accumulate large amount of water during the brief raining reason.
 * In some xerophytic plants, stem becomes succulent which are called the 'fleshy
 Xerophytes' as in Opuntia and Euphorbia.
 * Those succulent xerophytes in which leaves become fleshy; are also known as
 malacohyllous xerophytes', such as Aloe, Bryophyllum, Agava, Yucca etc

9. 3) Non- Succulent Perennial ( Drought Resisting Plants)
 * These are drought resistant plants and called as the true xerophytes.
 * They possess a number of morphological, anatomical and physiological
 characteristics, which enable them to withstand critical dry condition. Thus
 they suffer from dryness both in their internal as well as external environments.
 * They exhibit rapid root growth and form an extensive root systems to maximize
 water supply from the soil. The leaf size is greatly reduced and in many xerophytic
 grasses, leaves roll on to reduce the leaf surface for restricting loss of water due to
 transpiration. Some of the examples are Calotropis procera, Acacia nelotica
 Casuarina, Nerium, Saccharum, Pinus and Salvadora.

11. ECOLOGICAL ADAPTATIONS IN XEROPHYTES
Morphological Features (Adaptation)-
Root :-
Xerophytes develop under water deficient condition and in order to secure water,
the root system in xerophytes are well developed and show following characteristics :-
* Root system is well developed. Profusely branched . It is very extensive and
more elaborate then shoot system in true xerophytes.
* Roots of perennial xerophytes reach greater depth to absorb water but some
xerophytes have shallow root system especially when water is available in the
surface layers
* Roots are long, tap roots, with extensive branching spread over wide areas.
* Root hairs and root caps are very well developed.

12. Roots

14. Stems :-
 * Stems are mostly stunted, woody , dry, hard, ridged and covered with thick bark.
 * In some xerophytes as Saccharum, stem becomes underground, whereas in
 Opuntia it becomes fleshy, green, leaf-like covered with spines. In Euphorbia also
 it becomes fleshy and green.
 * Stems are covered with dense hairs ( Calotropis), coated with wax (Opuntia)
 or silica (Equisetum).
 * Stem in some xerophytes are modified into thorns ( Ulex).
 * Succulent and bulbous xerophytes can store water in their stem. e.g. Cactus and
 some species of Euphorbia.
 * In succulent xerophytes the stems are modified into structures like phylloclades,
 cladophylls or cladodes.

15. Stems

16.  a) Phylloclades - Stem modified into flattened leaf like organs (Opuntia)
 b) Cladophylls - Branches developed in the axil of scale leaves, become
 metamorphosed to leaf-like structure ( Ruscus)
 c) Cladophyll - Many axillary branches become modified into small
needle like
 green structures which look exactly like leaves (Asparagus).

18. Leaves
 Usually leaves of xerophytes are reduced or modified to various kinds of structure
 to minimise transpiration.
 * Leaves are usually absent in many xerophytes or they fall very early (caducous).
 * In majority of the xerophytes the leaves are modified into spines or scales as in
 Casuarina, Asparagus . Lamina may be long narrow or needle-like as in Pinus or
 divided into many leaflets as in Acacia.
 * Foliage leaves, wherever present, may become thick, fleshy and succulent, or
 tough and leathery in texture.

19. Leaves
 Leaf may modified into phyllode (Leaf petiole or rachis modified or flattened into
 leaf like organ) in some plant e.g. Acacia.
 * leaves of some xerophytes posses reduced leaf blades or pinnate and have very
 ` dense network of veins.
 * In some xerophytes especially those growing in high wind blowing area, the under
 surface of the leaves are covered with thick hairs which protect the stomatal guard
 cells and check the transpiration. These xerophytes are known as trichophyllous.
 * Leaf surfaces are shiny glazed to reflect light and heat, e.g. Calotropis

20. Leaves