Lygodium japonicum

Lygodium japonicum (Thunb.) Sw.
(of Japan, in reference to where it is was originally described from by Carl Pehr Thunberg, a student of Linnaeus and author of Flora Japonica—Thieret 1980)

Local names: Japanese climbing fern

Terrestrial; rhizomes subterranean, 2–3 mm in diam., creeping, bearing petioles 2–7 mm apart; leaves with indeterminate growth, climbing, vine-like, to at least 6 m long (reports of leaves to 30 m), the rachis (= midrib) elongate, twining, flexuous, stem-like (true stem/rhizome below ground), bearing numerous pinnae, continuing to elongate and produce additional pinnae; pinnae reduced to short stalks, these short stalks each bearing a pair of opposite pinnules and typically a dormant apical bud; pinnules usually 2–3-pinnate, sparsely to moderately pubescent on the lower (= abaxial) surfaces, the ultimate segments (= smallest subdivisions) of pinnules serrulate; fertile pinnules toward leaf apex, similar to sterile pinnules except having ultimate segments fringed with finger-like fertile lobes; sori (each with 1 sporangium) in 2 rows, 1 on each side of midvein of oblong marginal lobes of ultimate segments, almost completely covered by broad hood-like flaps or flanges of tissue which serve as indusia; n = 58, 2n = 58 (Roy & Manton 2006). Naturalized in low woods, thickets, roadside ditches, circumneutral soils; Hardin (e.g., V.L. Cory 59153, BRIT), Harris, Jasper (Correll & Correll 12529), Jefferson, Orange, Polk (all BRIT, TEX-LL), Liberty, Montgomery (TAMU, TEX-LL), Tyler (TAES, TEX-LL), Sabine (ASTC), San Jacinto, and Walker (TEX-LL) cos. in s part of the Pineywoods, Madison Co. (TAMU; Neill & Wilson 2001) at the e margin of the Post Oak Savannah, and Brazoria and Chambers (SBSC) cos. in the n Gulf Prairies and Marshes; in some areas (e.g., Jack Gore Baygall Unit of the Big Thicket National Preserve in Hardin Co.) it is so abundant and integrated into the vegetation that it appears native (G. Diggs, pers. obs.). Sporulating Apr–frost. Native of e Asia (China and Japan), India, and ne Australia, now naturalized in the se U.S. from NC s to FL w to AR and TX (Nauman 1993a) and also in Hawaii and Puerto Rico (Robinson et al. 2010). [Ophioglossum japonicum Thunb.] This widely cultivated, introduced species has been reported as invasive in a number of countries including some areas of the se U.S.; its dense canopy can prevent the growth of underlying vegetation (Nauman 1993a; Robinson et al. 2010). It escaped from cultivation in the se U.S. prior to 1906 and was first discovered in TX in 1937 (Soxman 1939; Nelson 2000). It is listed as a category I invasive exotic pest species by the Florida Exotic Pest Plant Council (FLEPPC 2009). Volin et al. (2004) listed a number of characteristics that enhance the competitive ability of non-indigenous plants, including “self or wind pollination, rapid growth to reproductive age or size, high and continuous seed or spore production, adaptations for short- and long-distance dispersal, and vegetative as well as sexual reproduction.” Lygodium japonicum has all of these except vegetative reproduction. (A second Old World species, Lygodium microphyllum (Cav.) R. Br., old world climbing fern, is also considered a dangerous invasive weed in Florida (Pemberton 1998, 2003; Pemberton & Ferriter 1998; Nauman et al. 2000; Brandt & Black 2001; Volin et al. 2004; Hutchinson & Langeland 2010) and is listed as a category I invasive exotic pest species by the Florida Exotic Pest Plant Council (FLEPPC 2009). It can be distinguished from L. japonicum by its 1-pinnate pinnules than are glabrous beneath. Currently it is known in the US only in FL.

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