AQUATIC PLANTS, a term applied to plants growing in or belonging to water. All vegetation was probably aquatic at first, cer tain plants becoming terrestrial by degrees. Numerous plants are, moreover, in the strict sense of the word aquatic, having never ac quired or having lost all direct connection with the soil. The algae are mainly aquatic, though many occur in damp situations on land, or on other organisms, while others remain for long periods quiescent in comparative dryness. Many algae are absolutely isolated in the water, while others are more or less intimately fixed to some solid substratum. Fungi are very sel dom found in water, and lichens are also em phatically terrestrial. Some liverworts, again, occur floating in lakes, but the majority grow in very dam places and mark the transition to the generally terrestrial life of mosses and ferns. Some rhizocarps, such as Salvinia, are aquatic, with leaves rising to the surface, while others are land or marsh plants, like the higher horsetails and club-mosses.
Among the flowering plants, or phanero gams, a return to aquatic life is exhibited by numerous though exceptional cases, while a very large number grow in moist situations and have a semi-aquatic habit. The simple mono cotyledons, known as Helobi z, or marsh lilies, are more or less strictly water-plants. The
arrowhead (Sagittaria), and other Alisma cea; the Butomis of the marshes; Hydrocharis, with floating kidney-shaped leaves; the water soldier (Stratiotes), with narrow submerged leaves; and the Canadian pond-weed (Anacha ris), which, though entirely flowerless in Eu rope, threatens to choke some canals and lakes, are familiar representatives. The little duck weed (Lemno), floating on the surface of stag nant pools, is one of the commonest aquatic monocotyledons; and the pond-weeds (Polo mca) found.in both fresh and salt water; the lattice plant (Ouvirandra), with its skeleton leaves; various estuarine and freshwater naia daceous plants—for example, Zostera and Naias, are also common instances, while those grow ing in marshy ground are far too numerous to mention. Among dicotyledons the white water buttercup (Ranunculus aquatilis), with its slightly divided floating and much dissected submerged leaves; the yellow and white water lilies (Nymphcea) ; the sacred lotus flower of the Ganges and Nile (Nelumbiuru) ; the gigan tic Victoria repia of tropical South America; and the insectivorous bladderwort or Utricu lariq, are among the more familiar aquatic forms.