Lygodium venustum, with no widely used common name other than climbing fern, which is applicable to all species of the genus Lygodium, is a fern native to tropical parts the Americas.
Description
With Lygodium venustum and other Lygodium species, what appears to be a twining stem with several compound leaves, or fronds, actually is just one big leaf, with the apparent stem being the leaf's twining rachis. The actual stem is a rhizome growing below ground or at the ground's surface. Keeping this unusual growth pattern in mind, here are other key features of Lygodium venustum:
The subterranean rhizome reaches up to
The leaf's rachis is straw-colored, wiry, twining, variously hairy and with indeterminate growth. Leaves may become 3-4 times pinnately compound. The first-order leaflets, or pinnae, produce two side subdivisions, or "pinnules." The pinna's central lobe is much the largest, up to 10 cm (4 in) long and 1.4 cm (1⁄2 in) wide. Margins are finely toothed.
Spores are produced on cylindrical lobes about 1 mm (1⁄32 in) wide growing at the margins of the leaf's ultimate divisions, the "fertile pinnae." Each lobe bears two rows of sporangia, one row on each side of a midvein, with each sporangium covered by yellow, pocket-like flaps of tissue serving as "indusia." The flaps bear white hairs up to 0.5 mm (1⁄64 in) long.
A plant's first juvenile leaves grow only up to about 20 cm (8 in) long and may be deeply cut longitudinally. The rachis rapidly elongates near the leaf's tip, but its pinnae expand slowly. Pinnae have terminal "dormant buds," which begin growing if the main leaf tip is injured or destroyed. If this happens, the dormant buds may develop branching patterns as if they were entire leaves, thus greatly diversifying the leaf's structure. Over half of the leaves may die within their first 3 months, while over 10% can survive for up to 30 months.
