Najas L.

(Mostly) fragile, slender, submersed annuals, rooting from the base and lower nodes. Stems often forked, terete, sometimes provided with teeth (subg. Najas). Leaves sessile, in pseudowhorls of 3 or more, linear, sometimes more or less subulate or linguiform, 1-nerved; midrib bordered on both sides, especially clearly visible in the lower part of fullgrown leaves, by a mostly distinctly transversely septated intercellular space, here called 'cavity'. Sheath more or less auricled, or truncate, or decurrent; upper part of the sheath and margin of the blade, sometimes also the dorsal surface of the midrib, spiny-dentate or spiny to various degree; spine cells yellowish-brown, ascending. Sheath with 2 axillary intra vaginal scales (see Fig. 2g-l). Plants mostly monoecious. Flowers small, unisexual, solitary or sometimes 2-4 together, at the very base of an (sometimes very short) axillary shoot, each often enclosed in a membranous (sub)sessile spathe (female fl. in Mal. spp. espathaceous). Spathe tapering to the top, or constricted into a cylindrical neck, the edge mostly with some erect spines. Male flowers consisting of one subsessile or stalked anther, which is tightly enveloped by a membranous 'perianth' apically mostly produced into 2 more or less distinct 'lobes'; anther 1-or 4-(rarely 2-)celled, basifixed, ± pore-like dehiscing at the top; 'pedicel' mostly considerably elongating just before anthesis. Female flowers (in Mal.): ovary subsessile, naked, elliptical to oblong, 1-celled, style cylindrical, with (1-)2(-4) linear, often unequal stigmas. Ovule one, basal, erect, anatropous; integuments two. Fruits elliptical-oblong (to ovate); style and stigmas persistent; pericarp very thin in the herbarium, not dehiscent, tearing away at the base or dwindling by rotting. Seeds oblong (to ovate), with a conspicuous raphe and a hard, (in Mal. spp.) distinctly areolate, mostly brownish testa; embryo straight; hypocotyl and radicle large, plumule well developed; cotyledon terminal, blunt. No endosperm.

Mostly in shallow, stagnant or sluggish waters, ditches, rice-fields, small streams in forest, pools, ponds, swamps, mostly in freshwater, but also in brackish water near coasts and inland, a few species even preferring this habitat. N. malesiana is the only species which is preferring streams and ponds in forests. The others are all found in eutroph waters. According to SUNIER ( SUNIER Treubia 2 1922 190 ) N. indica is usually found in freshwater sites but occurs in the brackish fish-ponds near Djakarta with a salinity of up to 32 °/00. N. browniana seems almost confined to coastal brackish water and is found inland only in the saline, water of the Kuwu mudwells, SE of Semarang, as the only aquatic represented there. Further N. marina var. zollingeri is confined to the alkaline waters of Batur Lake, in Bali, with a rather high content of dissolved minerals. Stems and leaves of Najas are not seldom found encrusted with calcium which adds to their brittle nature. Some species are resistant to rather hot water, e.g. N. tenuifolia subsp. pseudograminea var. pseudograminea which is found in the craterlake of Mt Kelud, Central Java, on black mud in water of 60° C; this water contains the usual large amount of minerals in solution common in craterlakes, further sulphates, sulphides, Ca and Mg compounds, etc. BRANDIS recorded N. graminea from a hot spring in Burma in water of 92° F, and the first record of it in England was from hot water emitted by a factory ( BRANDIS J. Bot. 22 1884 326 ). HERMANN recorded N. marina from hot springs in America ( HERMANN Leafl. West. Bot. 1 1935 182 ).As to depth Najas species are adapted to shallow waters; during the German Limnological Sunda Expedition the greatest depth at which Najas occurred was fixed at c. 5 m, but these specimens proved all to be sterile (cf. VAN STEENIS Arch. Hydrobiol. Suppl 11 1932 240, 271 ).The relatively rare occurrence of N. marina in Malaysia and in many parts of its almost ubiquitous range as well, points to a sensitive and selective ecology rather than to random chance dispersal by aquatic birds, especially in connection with its raciation into geographical varieties of sometimes restricted areas. The phenomenon is also found in Hydrocharitaceae and Alismataceae (cf. Fl. Mal. I 5 1957 317 ). In checking localities it has appeared that generally one lake seems to have only one species; N. indica in Toba, Ranau, Situ Bagendit, Singkang, and Gorontalo lakes, N. graminea var. graminea in Situ Gunung, Matana & Towuti lakes, N. tenuifolia subsp. pseudograminea var. pseudograminea in Kelud and Rawa Bening (Kediri) lakes, and the same holds for N. browniana and the three varieties of N. marina which are all found in one lake only, with no other species present. The only exception is Tondano lake, in NE. Celebes in which according to the data on the labels three species have been collected, viz N. graminea var. graminea, N. indica, and N. tenuifolia subsp. pseudograminea var. celebica.As to altitude most species and localities prefer the lowland areas, but N. marina goes up to 1000 m, and several others are found in Toba Lake, 900 m, Tondano Lake, 700 m, Kelud Lake, 1000 m, the highest altitude recorded being 1400 m. In the Himalayas Malaysian species are recorded to over 2000 m.As to climate none of the species shuns the seasonal areas, and some seem often to be more abundant in them than in everwet areas which may again point to preference for eutroph water.

Uses. According to SUNIER ( SUNIER Treubia 2 1922 222 ) Najas, which is profusely found in brackish fishponds (tambaks) near Djakarta, may be important as a source of food for fish. From the Toba Lake it is reported that Najas can be utilized as pig food, a use it shares with many other water plants ( BACKER Teysmannia 1911 514 ).