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FOC | Family List | FOC Vol. 23 | Hydrocharitaceae

1. Najas Linnaeus, Sp. Pl. 2: 1015. 1753.

茨藻属 ci zao shu

Herbs, annual, small, submerged in fresh or brackish water. Stem slender, fragile, much branched, rooting at base and lowermost nodes. Leaves subopposite or pseudowhorled, sessile, linear, small, 1-veined, sheathing at base, margin spinulose-toothed; sheaths variously shaped, often auriculate. Plants monoecious or dioecious; flowers minute, unisexual, solitary or few in leaf axil. Male flowers spatulate or rarely not spatulate; perianth (often named "involucre" or "envelope") 2-lipped, membranous, closely applied to anther; stamen 1, anther subsessile, 1-4-thecous, dehiscing at apex. Female flowers sessile; spathe absent or rarely present; perianth persistent. Fruit an elliptic-oblong achene; pericarp thin, membranous, indehiscent, persistent. Seeds without endosperm; testa hard, brittle, pitted; embryo straight.

About 40 species: cosmopolitan; eleven species (one endemic) in China.

One of the Fl. China editorial committee, Wu Zhengyi, prefers to keep the Najadaceae separate because of its distinct morphology in having superior ovaries and nuclear endosperms.

1 Plants dioecious; stems and abaxial surface of leaves usually spiny; areoles on seeds irregularly arranged.   1 N. marina
+ Plants monoecious; stems and abaxial surface of leaves usually not spiny; areoles on seeds longitudinally arranged   (2)
2 (1) Anthers 1-thecous   (3)
+ Anthers 4(or rarely 2)-thecous   (6)
3 (2) Seeds with many transversely elongated ladderlike pits; areoles fusiform; fruit narrowed and slightly curved at apex.   2 N. minor
+ Seeds with many longitudinally elongated pits; areoles rectangular or polygonal; fruit usually straight   (4)
4 (3) Auricles broadly triangular; leaves in pseudowhorls of 3.   5 N. browniana
+ Auricles orbicular or obcordate; leaves in pseudowhorls of 5   (5)
5 (4) Male spathe present.   3 N. gracillima
+ Male spathe absent.   4 N. pseudogracillima
6 (2) Auricles broadly triangular to linear   (7)
+ Auricles rounded to obcordate   (8)
7 (6) Male flowers without spathe.   10 N. graminea
+ Male flowers with spathe.   11 N. pseudograminea
8 (6) Fruit semilunate; female flowers with spathe.   6 N. ancistrocarpa
+ Fruit elliptic; female flowers without spathe   (9)
9 (8) Areoles hexangular, transversely elongated, arranged in ladderlike manner.   7 N. oguraensis
+ Areoles rectangular or irregularly arranged   (10)
10 (9) Auricles orbicular; testa with apparently raised cell walls.   8 N. chinensis
+ Auricles obcordate; testa without raised cell walls.   9 N. foveolata

  • List of lower taxa


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