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6. Hydrocharitaceae

水鳖科 shui bie ke

Authors: Qingfeng Wang, Youhao Guo, Robert R. Haynes & C. Barre Hellquist

Herbs, annual or perennial, submerged or floating, aquatic, in fresh or brackish water or marine. Stems short or elongated, sometimes stoloniferous. Leaves radical or cauline, alternate, opposite, subopposite, whorled, or pseudowhorled, sessile or petiolate, usually sheathing at base. Flowers unisexual or bisexual, actinomorphic, enclosed in a bifid spathe or within 2 opposite spathal bracts, or rarely not spatulate; spathes sessile or pedunculate. Stamens 1 to many, occasionally some staminodal; anthers 1-4-thecous. Ovary inferior, 1-loculed; carpels 2-15, fused; ovules few to many, on parietal, sometimes intruding placentae; styles 2-5; stigmas usually bifid. Fruit a fleshy and berrylike capsule dehiscent or opening by decay of pericarp, or an achene (Najas). Seeds numerous, usually small, without endosperm; embryo straight.

Eighteen genera and ca. 120 species: widely distributed in tropical and subtropical regions of the world; 11 genera (one introduced) and 34 species (four endemic, one introduced) in China.

Wang Huiqin & Sun Xiangzhong. 1992. Hydrocharitaceae. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 151-190; Zhou Lingyun, You Jun & Zhong Xiongwen. 1992. Najas. In: Sun Xiangzhong, ed., Fl. Reipubl. Popularis Sin. 8: 108-125.

1 Fruit an elliptic-oblong achene; perianth 2-lipped; plant annual, submerged in fresh or brackish water; leaves sessile.   1 Najas
+ Fruit a fleshy and berrylike capsule; perianth segments free, 1- or 2-seriate, 3 per series, outer often sepaloid, inner petaloid; plant perennial or annual, floating or submerged; leaves petiolate or sessile   (2)
2 (1) Marine herbs; pollen grains threadlike   (3)
+ Freshwater herbs; pollen grains not threadlike   (5)
3 (2) Plants slender; leaves usually opposite or binate, not in 2 rows, linear to ovate, usually petiolate.   10 Halophila
+ Plants robust; leaves alternate, in 2 rows, ribbonlike, sessile   (4)
4 (3) Female inflorescence shortly pedunculate; leaves smaller, slightly falcate.   5 Thalassia
+ Female inflorescence long pedunculate; leaves larger, not falcate.   4 Enhalus
5 (2) Leaves all basal; stems short   (6)
+ Leaves cauline; stems elongated   (9)
6 (5) Leaves linear, ribbonlike, sessile; fruit narrowly cylindric   (7)
+ Leaves lanceolate to orbicular, usually petiolate   (8)
7 (6) Stamens 3-9; ovary attenuate into a long, filiform beak; peduncle of female flower shorter.   6 Blyxa
+ Stamens 1-3; ovary not as above; peduncle of female flower very long.   7 Vallisneria
8 (6) Stolon absent; leaves submerged; spathes usually winged.   2 Ottelia
+ Stolon present; leaves floating; spathes not winged.   3 Hydrocharis
9 (5) Leaves whorled   (10)
+ Leaves alternate, opposite, or spirally arranged   (11)
10 (9) Leaves distinctly serrate to unaided eye.   9 Hydrilla
+ Leaves minutely serrate, magnification needed.   11 Egeria
11 (9) Flowers usually bisexual; sepals linear to lanceolate, shorter than petals; leaves with prominent midvein.   6 Blyxa
+ Flowers unisexual; sepals ovate, subequal to petals; leaves lacking a prominent midvein.   8 Nechamandra

  • List of lower taxa


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