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NZ Plants

Tmesipteris sigmatifolia - fork fern

Family: Psilotaceae

Tmesipteris sigmatifolia is occassionaly terrestrial but usually an epiphyte on tree fern trunks. It has a creeping stem (rhizome) that lacks roots, absorbing water instead with filamentous rhizoids. A pendulous and undivided aerial stem is formed that lacks true leaves, functioning instead with scale leaves. Scale leaves have a sigma-shape (a shallow S-shape), are spirally arranged, bright green, narrow, tapering to a long spine-like tip and brittle. Small round-ended sporangia are fused in pairs and lie on the upper surface at the base of forked fertile leaves.

An uncommon fork fern found in the northern half of the North Island with scattered populations on the South Island. 

Vegetative characteristics

Fertile scale leaf and sporangia

Plant form: pendulous unbranched stem, up to 30 cm long

Distribution, appearance: mostly on the upper portion of stem; forked, same size as sterile leaves

Scale leaf arrangement: spirally arranged

Sporangium location: upper surface of fertile scale leaf

Scale leaf shape: shallow S-shape, with blunt or truncate ends and a long, spine-like tip

Sporangium position: at base of of fertile scale leaf

Scale leaf size: up to 25 mm long

Sporangia distribution: in a fused pair (synangium) of unequal size, very small

Scale leaf surface: bright green to dark green, leathery

Sporangium shape: with round ends