Plants found in places where excess of water is present are called hydrophytes. Such plants develop the following morphological and anatomical adaptations.
(1) Roots :
(i) Root system is very much reduced in some floating plants (Wolffia, Utricularia) and in submerged plants (Ceratophyllum) the roots are absent.
(ii) Root hairs are usually absent except in those which grow in mud. Lemna minor lacks root hairs.
(iii) In Eichhornia, Trapa and Pistia no root cap develops but instead an analogous structure called root pocket is formed.
(2) Leaves :
(i) In some plants, the leaves are characterised by waxy coating which checks wilting and clogging of stomata by water e.g., water lily (Nymphaea).
(ii) Leaves are usually long ribbon like (e.g., Potamogeton) and finely divided e.g., Ranunculus Dissected leaves offer less resistance to the currents of water.
(iii) In some plants leaves of different forms are produced by the same plant, aerial leaves are not dissected but those leaves which are submerged are dissected. This condition is called heterophilly e.g., Ranunculus aquatilis.
(iv) In some acquatic plants e.g.. Nymphaea the petioles are long and spongy and they can adapt themselves to the varying depths of water and thus they keep their lamina on the surface of water.
(v) The leaves are usually thin and linear showing reduction in thickness and show an increased surface for the reception of diffused light.
(vi) The epidermis is thin and without cuticle. Epidermal cells have chloroplasts.
(vii) Submerged plants have vestigeal stomata.
(3) Stem :
(i) In some aquatic plants the stems are long, slender, soft and spongy which can bend easily in each and every direction.
(ii) Vegetative reproduction is the characteristic feature of most hydrophytes.
(iii) In some water plants food is stored in rhizomes (e.g., Water lily) and in others it is stored in tubers (e.g., Sagittaria).
(iv) Majority of water plants, at least spermatophytes are perennials.