Lastrea glabra Brack.; Aspidium glabrum (Brack.) Mett.; A. glabrum var. ambiguum Hillebr.; A. glabrum var. quadripinnatum Hillebr.; Nephrodium glabrum (Brack.) Baker; N. rubiginosum (Brack.) Hook. var. nudicaule Hook.; Phegopteris dicksonioides Mett.

Common names: kilau, hohiu (P. & E.)

Endemic

Latin glabra, without hair, bald, in reference to the general lack of scales on this species.

Plants medium-sized (rarely small), terrestrial. Rhizomes decumbent to erect, short-creeping, abundantly scaly. Fronds erect to spreading or pendent, up to 100 x 40 cm. Stipes not erect, arising at angle from rhizomes, chestnut brown to straw-colored, glabrous or scaly only at base, or stiffly erect. Blades 3-to 4-pinnate, in one plane (flat), sometimes 3-dimensional, ovate-deltate to tri-angular, 1-2.5 x longer than wide, light to dark green, glabrous above with scattered hairlike scales below, chartaceous, glandular to very glandular; rachises glabrous. Pinnae elongate-triangular, costae and veins with few to no fine scales. Pinnules elongate-oblong to linear-acuminate. Ultimate segments rounded to truncate, (1-)2.5-3.0 mm wide, separated, dentate margins sometimes more or less curved upward on living specimens. Veins free, mostly forked. Sori submarginal to marginal, usually in or near sinuses between 2 lobes of ultimate segments, mostly less than 1 mm diam. Indusia present, round, some-times difficult to find on older dried specimens.

Common to abundant in mesic to wet for-ests, usually at higher elevations, 460-2,200 m, on all major islands.

This species is extremely variable in the following characters: size, abundance of glands, degree of cutting, size, crisping, scali-ness, types of scales, stipe diameter, degree of separation of pinnae and ultimate segments, and shape and size of pinnae and ultimate segments. Variation in all the above characters forms a continuum with the varieties (i.e., all varieties are glandular to some extent, and there is no absolute character, such as the presence or absence of hairs, to clearly distinguish them). In nearly all cases, forms intermediate between var. glabra and the other varieties can be found growing nearby. These extreme forms are similar to and remind one of forms and varieties found in Dryopteris species grown in horticulture.

Hillebrand (1888) mentioned a similarity between D. glabra and D. aemula (Aiton) Kunze (the hay-scented fern) of the British Isles, Madeira, and the Azores. He treated D. glabra as a separate species because of its many varieties, feeling that such variation was lacking in D. aemula. Hillebrand also briefly described Aspidium glabrum vars. ambiguum and quadripinnatum, neither of which is recognized here. Neither has been studied with reference to his collected material in Berlin.

Dryopteris glabra may be recognized by its 3-to 4-pinnate blades, marginal to sub-marginal sori with indusia, slightly to very glandular blades, and rachises, costae, and veins with few scales (with the exception of var. hobdyana, which is quite scaly).