Hydrophytes are plants that live in abundance of water or in wet places. They are either partially or wholly sub- merged in water, when they are found in abundance of water. When they are in wet places, their roots or rhizomes are exposed to sufficient water.
Types of hydrophytes
An aquatic environment, in general, provides the following conditions for the plant:
(i) A matrix for plant growth.
(ii) Availabilitv of nutrients in dissolved state, (m) Minimum fluctuations in temperature.
(iv) Decreased availability of light and oxygen with the increase in depth.
(v) Water movements, weak or strong.
Xot all the conditions described above are encountered by every hydrophyte because they show different types of distribution. Basing on their relation to water and air, hydrophytes are grouped into the following categories.
(i) Submerged hydrophytes
(ii) Floating hydrophytes
(iii) Amphibious hydrophytes
I. Submerged hydrophytes
These are plants that grow in water, totally submerged and are not in contaxt with atmosphere. These plants are cither free floating (Ceratophyllum, Myriophyllum, and Utricularia etc.) or rooted (Ilydrilla, Vallisneria, Potamogeton, Chara, Nilella etc.).
II. Floating hydrophytes
Plants that float on the surface or slightly below the surface of water but arc in contact with air is called floating hydrophytes. These plants are either free floating or rooted to substratum.
(i) Free floating hydrophytes: These plants float on or just below the surface of water but are not rooted to the soil. Duck weeds (Lemna and Wolffia), water hyacinth (Eichhornia crassipes) and water ferns (Azolla and Salvinia) are examples of this category.
(ii) Floating but rooted hydro- phytes: This category includes plants that are rooted to the substratum of their habitat (pond, lake or river) but their leaves and flowering shoots cither float on the surface of water or just emerge out of water. Lotus (Nelumbium) and water lily (Nymphet) are examples of this category.
III. Amphibious hydrophytes
These are plants that are partly in water and partly in air. The aquatic part may be in shallow water or muddy sub-stratum. Morphological and anatomical features of these plants are different in parts that are in direct contact with water and the parts exposed to air. In some plants of this category like Ranunculus and Sagittarian the roots and parts of shoot are in water; whereas in others like Scirpus and Cyperus (Fig.6.6), have their roots in water, but their shoots
are completely exposed to air. The second categories of amphibious hydrophytes plants are also called marshy plants. There is also a category of plants which are partly submerged only when there is inundation of sea water. Such plants are called halophytes.