From the very begining of the formation of the earth, the environment is regularly being changed day by day. As a result, each and every organism in here, need to make itself fit with the changes of the environment. From that perspective, adaptation is a compulsory and must present issue in at every organism born and survive/d here. It is a process in which the organism/s fit themselves with the surroundings by developing new functions, organs, structures and so on.
In this article, we have discussed about the adaptation process and features in the hydrophytic and xerophytic plants.
- Related article- Adaptation of Plants.
The plants which grow in water partially or completely are known as aquatic plants or Hydrophytes.
Water may be fresh or saline.
- Roots may completely be lacking (Wolffia, Utricularia) or feebly developed (Hydrilla).
- Root hairs are absent (Lemna) or feebly developed.
- Root caps may be absent or root pockets are present (Eichhornia).
- Roots are generally fibrous type and adventitious, unbranched or sparsely branched.
- The stem is long, slender, weak, spongy and flexible type in submerged hydrophytes.
- The stem is short, stoloniferous, thick, and spongy, with extensive parenchyma in free floating plants.
- Root to shoot ratio is less than 1.
- Leaves may arrange in alternate phyllotaxy (Potamogeton) or opposite ( Cabwoman ) or whorled (e.g. Hydrilla sp.).
- Stomata are present on the upper epidermis which is in contact with air and gaseous exchange takes place through this stomata and lower surface is in touch with water.
- The upper leaf surface in floating leaves are coated with wax to prevent wilting.
- Partially submerged plants show heterophylly (presence of different types of leaves). e.g. Ranunculus aquatilis.
- The entire plant body covered with mucilage.
- The flowers and seeds are less abundant.
- Reproduction is mainly by vegetative methods.
- Excessive development of parenchyma and elaborate system of arenchyma (air spaces are huge) is present in hydrophytes.
- Poor development of vascular and mechanical tissues.
- Cuticle absent or poorly developed.
- Stomata are completely absent in submerged leaves.
- Chlorophyll is found in all the tissues.
- Mucilage canals and mucilage cells are present which secrete mucilage to protect the plant body.
- The reserve food is in the form of starch grains which occur in cortex and pith.
- Cystoliths (sclereids) of various shapes are seen in leaves and other tissues.
Xerophytes are plants which are adapted to dry/desert areas. They are a type of succulent plant. To survive these harsh conditions they have special features. For example, a cactus has white hairs which help to prevent water loss.
Some common examples of xerophytes are: Casuarina, Asparagus, Pinus etc.
1. The root systems are well developed with root hairs and root caps.
2. The roots are fasciculated.
3. Stems are usually stunted, woody, dry, hard, ridged, and covered with thick bark, may be underground, e.g. Saccharum. In Opuntia phylloclade is covered with spines.
4. Stem is covered with thick coating of wax and silica or dense hairs.
5. Stems may be modified into a thorn e.g. Ulex or cladodes e.g. Asparagus.
6. Leaves are very reduced, small scale-like, sometimes modified into spines or scales e.g. Casuarina, Asparagus.
7. Lamina may be narrow or needle like e.g. Pinus or divided into many leaflets e.g. Acacia or succulents e.g. Aloe.
8. Root to shoot ration is more than 1.
- Well developed vascular and mechanical tissues present.
- Thick cuticle is present in the epidermal layer.
- Sunken stomata are present.
- Leaves are succulent (e.g. Aloe sp.).
- Multilayered epidermis (e.g. Nerium sp.), sclerenchymatous and several layered hypodermis (e.g. Pinus sp.) are present.
- Mesophyll is well differentiated.
- Spongy parenchyma and palisade parenchyma are present.
- The stomata open during night hours and remain closed during the day. This unusual feature is associated with metabolic activities of these plants.
- The chemical compounds of cell sap are converted into wall forming compounds (e. g. Cellulose, Suberin etc.)
- Some enzymes, such as catalases, peroxidases are more active in xerophytes than in mesophytes.
- The capacity of xerophytes to survive in long period of drought is due to the resistance of the hardened protoplasm to heat and desiccation.
- Xerophytes have very high osmotic pressure, which increases the turgidity of the cell sap.
|Roots lacking or feebly developed.||Root system well developed.|
|Root hairs absent or feebly developed.||Root hairs present.|
|Root caps absent.||Root caps present.|
|Roots fibrous type and adventitious.||Roots fasciculated.|
Woddy, coverer with bark, may be modified into thorn or cladodes.
|Root to shoot ratio less than 1.||Root to shoot ratio more than 1.|
|Leaves are floating with stomata.||Small scale like leaves.|
|The entire plant body is covered with mucilage.||Mucilage covering absent.|