Mertensia pinnata Kunze; Dicranopteris g/abra (Brack.) Underw.; leichenia glauca sensu auct., non (Thunb.) Hook.; Hicriopteris glabra (Brack.) Ching; H. pinnata (Kunze) Ching; Mertensia glabra Brack. [Hillebrand's Gleichenia longissima Blume~ andy vars.]

Common names: uluhe lau nui (lau, leaf, nui, large: large-leaved uluhe)

Endemic

Latin pinnatus, winged, feathered, set in two opposite ranks, referring to the winglike appearance of the fronds.

See generic description. Pinnae 0.5-1.2 m long. Stipes flattened adaxially making half circles. Ultimate segments 3-12 mm long.

Common medium-sized to large fern, usually in wet forests, often on open ridges or on steep, wet banks and streamsides, in association with Dicranopteris linearis or Sticherus owhyhensis, 350-1,500 m, all major islands.

Diplopterygium has a pattern of indeterminate growth. In D. pinnatum the main stipe emerges from the underground rhizome erect and unbranched, and topped by an uncoiling fiddlehead. At some point, it ceases lengthening and 2 opposite pinnae form. At its terminus is a dormant (sometimes abortive) bud enclosed by a pair of small, leafy segments. After a period of dormancy, the rachises grow again and repeat the process. (There is no branching of the pinna rachises as seen in Dicranopteris and Sticherus.) This frond elongation repeats 2 or 3, sometimes more, times, resulting in a tangle of long fronds.

Diplopterygium pinnatum may be easily distinguished from the other members of the Hawaiian Gleicheniaceae by its unforked rachises (rachises of Dicranopteris and Sticherus show repeated dichotomous forking); its 1-forked veins associated with large pinnae and short ultimate segments (rather than 1-forked veins associated with long ultimate segments as in Sticherus); and fewer sporangia per sorus.