August in the hills with Chris Horne
Hymenophyllum dilatatum, matua mauku, irirangi
Origin of the names
Hymenophyllum means ‘membranous leaf’. The Greek word for ‘membrane’ is ‘hymen’, and for ‘leaf’ is ‘phyllon’; ‘dilatatum’ comes from the Latin word meaning ‘broadened, expanded’. Note: ‘irirangi’ is also the name of Hymenophyllum demissum described in July’s Tramper. Matua means ‘parent’, or more particularly ‘father’; mauku is the name applied to filmy ferns in general. There is no English name for matua mauku.
Distribution and habitat
Matua mauku grows on Te Ika a Māui/North Island, Te Wai Pounamu/South Island, and Rakiura/Stewart, Rekohu/Chatham and Auckland islands. It is common throughout, in coastal to montane forests, except for the drier parts of the eastern South Island. It usually perches as an epiphyte on trees; it also grows on fallen trunks, sometimes on banks, and rarely on the ground.
Matua mauku has a slender, wiry, long-creeping rhizome.
Matua mauku is NZ’s largest filmy fern, and one of the most distinctive in the genus. The stalks/stipes are 2-15 cm long, stout, smooth, with narrow wings for some of their length. The stems/rachises have broad wings along their length. The fronds are 8-40 cm long x 4-15 cm wide, ovate or narrowly ovate, bright green and smooth. The pinnae/segments are 2-3 mm wide. Because matua mauku’s fronds are mostly one cell thick and translucent, like those of Leptopteris hymenophylloides and L. superba, (Tramper May and June 2017), it can easily be confused with those two species when they are immature.
The spores are held in very broad sori which develop slightly sunk into the ends of the broad pinnae/segments – see image.
There are no recorded Māori or Pākeha uses for matua mauku. Where to look for matua mauku Look for this widespread fern when you tramp in lowland to montane forests, e.g., in Otari-Wilton’s Bush and in the Remutaka and Tararua ranges. Look for its smooth fronds with smooth margins, the broad flat wing along the stem/rachis and much of the stalk/stipe, and the very broad segments/pinnae. It is worth carrying a hand lens to study these features.