Macromitrium incurvifolium (Hook. & Grev.) Schwägr.

Plants robust. Branch leaves irregularly and strongly flexuose-twisted and with apices strongly inrolled and obscured when dry, widely spreading, flexuose, and not funiculate when moist, lanceolate, acute, c. 2.5 mm; margins entire; upper laminal cells in distinct longitudinal ranks, rounded-quadrate to subquadrate or oblate, 5–8 µm wide, slightly bulging, finely pluripapillose; mid laminal cells similar in size and shape but smooth; inner basal cells long-rectangular, with narrow and curved or weakly sigmoid lumina. Costa percurrent. Gemmae absent.

Pseudautoicous (fide Vitt & Ramsay 1985). Perichaetial leaves shorter than adjacent vegetative leaves, with long excurrent costae. Dwarf males not seen. Setae c. 5 mm, sinistrorse; capsules obovoid in N.Z. material, smooth or weakly 8-plicate, c. 1.5 mm. Peristome single, often fallen in dried material. Calyptra deeply and evenly lacerate, strongly plicate and hairy. Spores anisosporous, 15–39 µm.

Not illustrated. Vitt & Ramsay 1985, figs 268–269, 271–273, 275–284; Vitt et al. 1995, figs 16 a–j.

The difference in their leaf shape and the nature of their laminal cells make confusion between M. incurvifolium and the superficially similar M. ligulare and M. ligulaefolium unlikely.

Known from only a single, but ample and fruiting, collection (P. de Lange K588, AK 327888) from a fallen Kermadec Is pōhutukawa (Metrosideros kermadecensis) at c. 450 m elevation on Raoul I. The Kermadec Is material compares well to collections from Fiji.

The strongly crisped leaves are suggestive of the related M. gracile. However, in M. incurvifolium the inner perichaetial leaves are shorter than the adjacent vegetative leaves (the perichaetia are not obvious under a stereoscope), the branch leaves are consistently unbroken and lanceolate with inrolled and obscured apices when dry, and the calyptrae are hairy. In M. gracile, the perichaetial leaves are much longer than the adjacent leaves (and the perichaetia obvious), the branch leaves are usually fragmented, with decurved apices (if intact) when dry, and the calyptrae are naked or nearly so. The small upper and mid laminal cells that are arranged in very distinct longitudinal ranks also give M. incurvifolium distinction, but this is a feature that it shares with M. gracile. The two species overlap in distribution only on the Kermadec Is.

Vitt & Ramsay’s (1985) "M. gracile group" includes five species in Australasia, including M. incurvifolium, M. gracile, and M. helmsii.