Lygodium flexuosum (L.) Sw.
(=Ophioglossum flexuosum L.)
Family Lygodiaceae, Tribe Paniceae
Rhizomatous perennial fern, with climbing rachis up to 2.5 mm thick, slightly pubescent, subterete, flattened on one side, narrowly winged or tetragonous. Primary rachis branches 2–16 mm long. Secondary pinnae narrowly ovate to oblong or rarely palmate, 7–30 cm long, 4.5–12 cm wide, 1–2-pinnate. Stalks of the leaflets (pinnules) are shorter in length towards pinna apex. Ultimate pinnules are 1.5–10 cm long, 5–16 mm wide; sterile ones sometimes fused basally and palmately-lobed, membranous, glabrous or sparsely pubescent; base truncate; margins serrulate; veins free. Fertile pinnules similar in length or shorter than sterile ones. Sporogenous lobes 1.5–8 mm long. Spores finely verrucose.
Pinnule leaflet stalks that become shorter in length towards pinna apex distinguish this species from Lygodium microphyllum. Fronds are typically 2-pinnate in L. flexuosum versus 3-pinnate in L. japonicum.
Lygodium japonicum (Thunb. ex. Murr.) Sw. (non-FNW)
Lygodium microphyllum (Cav.) R. Br.
southeastern Asia southward to Australia; not currently known to occur in the U.S.
climbs trees and scrambles in open places in deciduous or mixed forests
Lygodium flexuosum is widespread in eastern Asia, adversely affecting rice crops and natural lowland vegetation. It has confirmed medicinal properties.