Mesophytes represent the group of plants that can neither grow in the complete aquatic habitat nor the scarcity of water or dry conditions. These are the land plants that show features similar to both hydrophytes and xerophytes. These grow under favourable conditions, where the concentration of water and temperature are not too much high and not too much low.
Both the vascular and mechanical tissue are highly developed and differentiated in mesophytic plants. Mesophyte plants require stable atmospheric conditions or temperate zone, where the conditions are not too dry and wet.
Meaning of Mesophytes
Mesophytes define as the community of terrestrial plants which can neither adjust in too wet nor in water-scarce conditions. It requires a moderate amount of hot and humid climatic conditions and develops in soil that provides an average dry-wet environment for the plant growth. Mesophytes constitute the largest ecological community of land plants. It includes two significant communities depending upon the ecological conditions, namely community of grasses and herbs and the community of woody plants.
Mesophytes are the group of plant species that involves two major communities.
The community of grasses and herbs
It includes perennial grasses and herbs, which further classifies into the Arctic and alpine mat grasslands and mat herbage, Meadow and Pasture on cultivated land.
The Arctic and alpine mat grasslands and mat herbage is a particular group of mesophytes that are ubiquitous in Polar Regions and mountain tops. It comprises of small-sized soft shrubs. The mat grasslands include members of the Gramineae family, and the examples of mat herbage include dicot herbs like Ranunculus, Saxifraga, Delphinium, Potentilla etc.
Meadow is the intermediate link between the mesophytes and hydrophytes that require moisture content of 60-83%. It includes the members belonging to the Compositae, Papilionate etc.
Pasture on cultivated land has a shorter period of vegetation, where the population or density of the plants is disturbed by grazing. It involves dicot herbs, grasses and mosses.
The community of woody plants
It includes bushlands and forests. The community of woody plants further classify into mesophytic bushlands, deciduous forests and evergreen forests.
In mesophytic bushlands, the temperature is not too much favourable for the forest plants, but too much feasible for the mat herbage vegetation, which includes plants like Arabis, Salix, and Lathyrus etc.
Deciduous forests are distributed in the temperate, cold or tropical regions where the annual rainfall is upto 80-150 cm. These are characterized by the periodic defoliation of leaves after every 5-8 months of foliation. It includes Betula birch forest, Quercus oak forest etc.
Evergreen forests are distributed in tropical and sub-tropical regions. These are common in the cold temperate zone of Southern Hemisphere. Sub-tropical evergreen forest is found in the areas with heavy rainfall, and the plants reach a length of 30 metres like the montane forest, pine forest etc. Tropical evergreen forest is found in low lying regions with an annual rainfall of 180 cm or more, and the plants are of 40-50 metres in height like palm forest etc.
Mesophytes contain a highly developed and branched root. Unlike hydrophytes, the roots comprise a root cap that protects the root tip from degeneration and promotes geotropic movement. These can develop perennating organs like corms, rhizomes and bulbs to store food and water.
The roots of monocot mesophytes comprise a cluster of the fibrous root system for the absorption of water, while the roots of dicot mesophytes comprise a well-developed tap root system. The root hairs are present abundantly for the uptake of water and minerals from the soil.
Mesophyte plants contain a wide, linear, branched, and hard stem that can be herbaceous or woody. These are generally aerial and profusely branched. The stem comprises an extensive network of mechanical and conductive tissues that mediates water and minerals conduction all inside the plant body.
Mesophytes consist of large, broad, narrow leaves with varying shapes and sizes. The dicotyledonous leaves of mesophytes include a large number of stomata on the lower leaf surface and few or none on the upper leaf surface. The stomata in monocotyledonous leaves generally contain the uniform distribution of stomata on both the sides of a leaf. It performs a significant role in the evaporation of excess water.
A protective waxy cuticle surrounds the aerial parts of the plant body and prevents excessive transpiration. Besides that, it also protects the internal tissues against physical, chemical, ecological or mechanical stresses.
It requires a more or less continuous water supply, but undergoes hardship in extreme conditions, as they lose water rapidly. Generally, mesophytes suffer water and temperature stresses.
Mesophyte plants that are growing in the rainy climate possess on especial organ “Hydathodes” that opens without the guard cells. The excessive water exudes out of hydathodes in the form of droplets by a process refers to as “Guttation”.
Leaves: These are comparatively thin and large, which increases the surface area for the absorption of light energy or increases the rate of photosynthesis.
Cuticle: As the leaves are larger, there will be excessive water loss. So to combat this condition, a waxy cuticle encircles the epidermis.
Mesophylls: It develops extensively and differentiates to aid gaseous exchange between the plants and surrounding.
Vascular bundles: It is well developed consisting of both xylem and phloem connective tissue. Xylem helps in the transportation of the absorbed water from the roots to leaves. Phloem helps in the conduction of organic minerals all around the plant. The vascular bundles allow the plants to keep water balance, by enabling the conduction of water and minerals from the leaves to all other parts of the mesophytic plants.
Roots: The root system in mesophytes are the well-developed structures that generally grows deep inside the soil that in turn provide anchorage to the plant. It also allows for efficient water and mineral absorption from the surrounding soil. Besides this, it also comprises of accessory structures like root hairs and root cap.
Therefore, we can conclude that the mesophytes are the group of plant system that grows under an intermediate range of temperature and moisture and acts as a connecting link between the hydrophytes and xerophytes.