Osmunda zeylanica Linnaeus, Sp. Pl. 2: 1063. 1753; Botrychium zeylanicum (Linnaeus) Swartz; Helminthostachys dulcis Kaulfuss, nom. illeg. superfl.; Ophiala zeylanica (Linnaeus) Desvaux.

Rhizome 4-8 mm in diam. Fronds usually single at rhizome apex, 20-60 cm tall; stipe base sheath ca. 1 cm; common stipe fleshy, 10-55 cm, 2-8 mm in diam., glabrous; sterile lamina ternate with basal pinnae divided into 3 or 4 pinnules; pinnules lanceolate, 6-20 × 1.5-3 cm, base decurrent, margin irregularly toothed, apex acute or rounded. Spikelike sporophore arising at top of common stipe; stalk 4-10 cm, spike 4-20 cm, 5-12 mm in diam., branches divided 1 or 2 times, each consisting of stalk bearing a pseudowhorl of sporangia and 1-4 forked sterile apical appendages. 2n = 188.

Helminthostachys zeylanica is a rare, endangered species in China because of over-collecting for use in traditional medicine and because of habitat change.

Forests, edges of marshes; low elevations. Guangdong, Hainan, Taiwan, Yunnan [widespread: Cambodia, India, Japan, Laos, Philippines, Sri Lanka, Thailand, Vietnam; tropical Australia, W Pacific islands].