Tmesipteris sigmatifolia Chinnock

Epiphytic ferns. Aerial stems pendent, 40–270 mm long, 10–35 mm wide, unbranched or rarely 1-branched, of indeterminate growth terminated by large sterile leaf or sporophyll. Leaves narrowly oblong or narrowly ovate, usually sigma-shaped, spirally arranged, shiny green on both surfaces, coriaceous; the longest 8–20 mm long, 2–4 mm wide, just above or just below mid-stem; apices slightly emarginate, truncate or cuspidate, with a mucro 1.5–3.5 mm long. Sporophylls mostly in the distal half of the stem or sometimes throughout except for the lowermost part. Synangia 2.5–5 mm long, 1–2.5 mm high; lobes often unequal in size or occasionally equal, round-ended; the lower surface of each lobe appressed to the subtending leaf margin along its length.

This species is recognised by its generally sigma-shaped leaves which are narrower than in other species and with a longer mucro tip. The synangia are usually located in the distal half of the stem, and the lobes are often unequal in size, with rounded ends.

Tmesipteris sigmatifolia grows epiphytically on tree fern trunks, most commonly on Cyathea dealbata and Dicksonia squarrosa, but also occasionally on Cyathea medullaris, Dicksonia lanata, and, at higher altitudes, on Cyathea smithii. It has been recorded once growing in litter at the base of a kauri (CHR 302370). It occurs in kauri, podocarp, broadleaved and old kānuka forests in northern New Zealand.

n = 104 (Brownsey & Lovis 1987).