Hymenophyllum villosum Colenso

Epiphytic, terrestrial or rupestral ferns. Rhizomes long-creeping, 0.4–0.6 mm diameter, bearing sparse to abundant pale or red-brown hairs up to 2 mm long, clustered at bases of stipes. Fronds 25–275 mm long. Stipes 5–100 mm long, dark brown or black, narrowly winged for most of their length, sparsely to abundantly covered in pale brown hairs. Laminae usually 4-pinnatifid or rarely 3-pinnatifid or 5-pinnatifid, ovate or broadly ovate or elliptic, 17–200 mm long, 12–110 mm wide, dark green, membranous, sparsely to abundantly covered in pale brown hairs on the costae. Rachises narrowly winged throughout, dark brown or black, often zig-zagged distally, sparsely to abundantly covered in pale brown hairs; rachis wings planate or slightly flexuose. Primary pinnae in 8–25 pairs, overlapping, winged throughout; distal portion of primary pinnae straight or slightly to strongly incurved acroscopically; distal primary pinnae ovate or elliptic or obovate, adnate; proximal primary pinnae narrowly ovate or ovate, adnate; the longest primary pinnae at or below the middle, 8–100 mm long, 6–30 mm wide. Secondary pinnae arising both acroscopically and basiscopically, scarcely overlapping, winged throughout, adnate; ovate or elliptic or obovate on distal primary pinnae; ovate or elliptic on proximal primary pinnae; the longest secondary pinnae 4–25 mm long, 3–10 mm wide. Ultimate lamina segments linear, up to 5 mm long, 0.4–1.2 mm wide, often recurved when dry; apices obtuse or truncate; margins entire, lacking a distinct border; distal segments on primary pinnae divergent. Sori borne on short acroscopic and basiscopic segments throughout pinnae in distal half of lamina, solitary, many on each primary pinna, adnate; indusia bivalvate; indusial flaps ovate, 1–2.5 mm long, about twice as long as broad, apices acute or obtuse, margins entire, outer surfaces smooth, sometimes hairy at base; receptacles included within indusial flaps.

Hymenophyllum villosum is a small to medium-sized filmy fern distinguished by its entire lamina margins, often black zig-zagged rachis, winged rachis and stipe, and hairy fronds. The fronds are often tightly coiled in exposed situations. Plants in the South Island generally have much hairier fronds and narrower ultimate segments (usually less than 1 mm wide) than those in the North Island which are sometimes only sparsely hairy. When dry it has a strong smell and stains paper dark brown or yellow. It is very similar to H. sanguinolentum, but is usually distinguished by its hairy fronds, narrower ultimate segments (0.4–1.2 mm wide cf. 0.8–1.5 mm wide), and indusial flaps which are usually about twice as long as broad and lack crests on their outer surfaces. The distinction between the two species is more obvious in the South Island where H. villosum is usually very hairy and has narrower ultimate segments. Hymenophyllum sanguinolentum generally grows at lower altitudes than H. villosum (0–900 vs 370–1300 m in the North Island; 0–850 vs 30–1650 m in the South Island). Nevertheless there is a significant zone of overlap and plants of both species occur together in several places.

Hymenophyllum villosum grows frequently with H. multifidum and the two can be confused, especially when sterile or the fronds are tightly coiled. However, they can always be distinguished by the entire lamina margin in the former, and toothed margin in the latter.

Occurs in podocarp, beech and broadleaved forest, in mānuka, kānuka and subalpine scrub, and in tussock and alpine herbfield, growing on the ground, on rocks and banks, on rock faces, under overhangs, on fallen logs and as an epiphyte. It has been recorded on trunks and branches of Archeria traversii, Dacrycarpus dacrydioides, Dacrydium cupressinum, Griselinia littoralis, Ixerba brexioides, Metrosideros umbellata, Olearia chathamica, O. colensoi, Phyllocladus alpinus, Podocarpus laetus, P. totara, Pseudowintera colorata, Quintinia serrata, Weinmannia racemosa and species of Nothofagaceae. It has also been recorded from the trunk of Leptopteris, but not from any tree fern species.

n = 34 (Daellenbach 1982), 36 (Brownlie 1954).

Hymenophyllum villosum was described by Colenso (1845) from collections he made in forests near Ruatāhuna in January 1842. The lectotype was chosen by Allan (1961), "WELT, near Ruatahuna, Colenso" (now WELT P003273). There is also a specimen at K (Colenso 288) which is a syntype (photo WELT E469/30). The date on the WELT specimen is 1841, rather than 1842 as in the protologue, but one or other is assumed to be incorrect.

For comments on plants of intermediate morphology between H. villosum and H. sanguinolentum, and their cytology, see Notes under H. sanguinolentum.