(4) 水蕨
Ceratopteris thalictroides (L.) Brongn.
水蕨科（Parkeriaceae）

英文名 (English name): Floating Fern, Water Fern

中國境內現狀: 易危 (VU)。 國家二級保護野生植物。
Status in China: Vulnerable (VU). Wild plant under State protection (category II).

形態特徵：水生或半水生生草本；根狀莖短，直立，生根於淤泥中。葉簇生，二型；葉柄綠色，肉質，中空，長度因水的深度而不同；不育葉二回羽狀分裂，通常長20-30厘米；羽片再作1-2次分裂，裂片線形。能育葉通常長於不育葉，二回羽狀分裂；小羽片分裂成線形裂片；末回裂片長1.5-4厘米，寬約2毫米，邊緣反卷，薄而透明。孢子囊沿能育葉裂片的縱脈兩側著生，並為裂片反卷的邊緣所覆蓋。
　　

地理分布：深涌、三椏村、荔枝莊、錦田、船灣和蒲台島。分布於廣東、廣西、台灣、福建、江西、浙江、山東、江蘇、安徽、湖北、湖南、四川、雲南等省; 世界熱帶及亞熱帶地區。
　　

生境與生態：生於池沼、水田或水溝的淤泥中，有時漂浮於深水面上。
　　

本種是少數生長於池沼和濕地的蕨類植物之一，代表一種特別的生態類型，有保護價值。此外，莖葉可供藥用。本種分布雖廣，但其生長環境很特殊，目前在世界各分布區的範圍正不斷縮小，個體數量亦日趨減少。

Description: Aquatic or semi-aquatic herbs. Rhizome short, erect, rooting in mud. Leaves clustered, dimorphous; stipes green, fleshy, hollow, variable in length according to the depth of water; sterile leaves bipinnatifid, usually 20-30 cm long; the lobes of the pinnae sometimes lobed again; fertile leaves usually longer than sterile leaves, bipinnate; pinnules divided into linear lobes, the ultimate lobes 1.5-4 cm long and about 2 mm wide, edges reflexed, thin translucent and colorless. Sori borne along the longitudinal veins and protected by the reflexed edges of the ultimate segments of pinnules.
　　

Distribution: Sham Chung, Lai Chi Chong, Kam Tin, Plover Cove, Po Toi Island. S and SW China; tropical and subtropical regions throughout the world.
　　

Habitat and Ecology: In ponds, paddy fields and other marshy or flooded areas.
　　

The species represents a special living form of ferns, and is thus of great botanical interest. The leaves and stems can also be used medicinally. Although the species is widely distributed in tropical and subtropical regions, it has a special habitat requirement and in recent years its distribution area and population size are decreasing.

參考文獻 (References)：
秦仁昌、邢公俠，1990: 中國植物誌3（1）: 275，圖版77：1-4。科學出版社。北京。
Edie, H. H., 1977: Ferns of Hong Kong, 241. Hong Kong Univ. Press, Hong Kong.
So, M.L., 1994: Hong Kong Ferns, 29. The Urban Council, Hong Kong.