Halophila ovalis (R. Br.) Hook. f.
本種葉在外形及大小上的差別極大;外形從橢圓形至倒卵形;長度從0.9至2.2公分;葉脈的數目自9至18對不等。葉片上常見紅褐色斑點,大小、數量不一,在某些地點分布者甚至占去大部分葉表(例如:澎湖群島城前),使得葉片呈現紅褐色,只有少部分是本種植物常見的綠色。依生長環境的水質不同,植株亦有差異,例如鹽田中生長者有質地較堅韌的匍匐莖,葉片較厚而不易撓曲,顏色偏向深綠。
Delicate annual herbs, dioecious. Roots 1 at each node. Rhizomes creeping, slender; internodes 3.5-18.0 mm, with 2 leaves at each node; scales 2, oblong to ovate, the apex membranous, transparent, the upper one 2.0-3.5 mm in length, the lower one 3.0-5.2 mm. Stems subsessilis. Leaves simple, in pair. Leaf blades greenish to browny green, glabrous, elliptic, oblong, or obovate, 0.9-2.2 cm in length, 4.3-8.5 mm in width; leaf apex rounded to obtuse; leaf margin entire, broadly undulate; crossing veinlets (9-)12-18 pairs, pinnate, often branching; petiole 1.3-4.0 cm in length. Spathes membranous, transparent, elliptic, ca. 5.1 mm in length, not keeled, cymbiform; apex acute. Staminate flowers solitary; tepals 3, membranous, transparent, cymbiform, ca. 4 mm in length, convex when matured, with a longitudinal dark band; stamens 3; anthers basifixed, ca. 3.7 mm in length. Pistallate flowers solitary; tepals wanting; ovary ovoid, 1.5-2.0 mm in length, the placentation marginal; style short, ca. 4.0 mm in length; stigmata 3, 1.2-1.7 cm in length. Fruits globose, long beaked. Seeds subglobose, ca. 0.83 mm in length, 10-14 in number; testa areolatus; caruncle yellow.
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This species is widely distributed in the Indian and the west of Pacific Oceans. It is also frequently found along the coast of East Africa, as south as temperate South Africa(den Hartog, Fl. Males., Ser. I, Spermat. 5(4): 408. 1957; Merrill, Enum. Philipp. Pl. Fl. 1: 26. 1925; Walker, Fl. Okinawa S. Ryukyu I. 151. 1976). In Taiwan and adjacent islands, it grows on various substrates, including intertidal muddy, sandy and coral sand substrate. It is flowering April to May.
除了單一種類的分布地點以外,卵葉鹽藻與其它線狀葉海草混生時通常會占據邊緣地帶,而較少在草床中間發現。以東沙潟湖為例,南岸為絲粉藻及單脈二葉藻混生,卵葉鹽藻僅在外圍生長,少量伸入其它海草的分布範圍;又如海口的珊瑚礁平台,本種僅在平台前端和稀疏的單脈二藥藻混生,平台內側石英沙覆蓋的區域均不見生長。