Synonyms: Polypodium unidentatum Hook. & Am.; Nephrodium unidentatum (Hook. & Am.) Diels; Phegopteris spinulosa Hillebr.; Ph. unidentata (Hook. & Am.) J. Sm.; Polypodium spinulosum (Hillebr.) Baker

Common names: 'akole (P. & E.)

Endemic                  

Latin unus, one, + dentatus, toothed, in reference to the frequently toothed ultimate segments.

Plants large, terrestrial. Rhizomes decum-bent to erect, up to 60 cm long. Fronds 1-2 m long. Stipes grooved, 30-100 cm long, straw-colored, scales linear-Ianceolate to deltate, dark to light brown, mostly act bases or covering entire stipes, dense or sparse on upper stipe. Blades 3-to 4-pinnate, oblong-lanceolate to oblong-ovate, 34-100 x 25-90 cm, dark green to yellowish green, coriaceous; rachises sparsely to heavily clothed with stiff, dark, deltate to deltate-lanceolate scales. Pinnae 10-24 pairs, 10-45 x 6-22 em, short-stalked, costae with sparse to plentiful scales similar to those on rachises. Pinnules stalked to nearly sessile, arising at 90° angle from costae, oblong-Ianceolate to oblong-ovate, 3-18 x 1-3 em, basal pinnules largest. Ultimate segments 2-4 mm wide, sessile to short-stalked, mostly lobed, base broadly cuneate, lobe tips broadly obtuse to acute, toothed. Veins prominent, free, forked. Sori marginal, close to sinuses. Indusia absent.

Locally common in isolated areas in wet forests, 460-1,750 m, all major islands.

This species varies greatly in size, density, and distribution of scales; in blade cutting; and in width, degree of lobing, and character of the marginal teeth of the ultimate segments. In some areas the population is uniform and appears distinct, but throughout its distribution a range of apparently fertile intermediates can be found. This variability makes it difficult to define the boundaries of any level of taxonomic recognition. The taxon in the past has been treated as one of three recognized varieties of D. unidentata, as a single species, as two species, and as a species with four varieties. Fraser-Jenkins (1994) reluctantly divided it into four varieties (vars. unidentata, paleacea, acutidens, and ukulelensis), but his descriptions lack objective measure-ments and show considerable overlap.

Dryopteris unidentata is treated here as a species with two varieties. The differences between the varieties are related to scale dis-tribution, frond size, degree of frond cutting, and width of ultimate segments, but there is a continuum of intermediates between them. Further collections, detailed measurements, scanning electron microscopy of the spores, isozyme and DNA studies, and common-garden studies would help clarify the relationships. It may be that more varieties or even another species may need to be recognized.

Dryopteris unidentata is probably monophyletic with D. sandwicensis and D. tetrapinnata. The smaller D. sandwicensis has scales limited to the bases of the stipes and lacks stiff dark scales on the rachises, although occasional hairlike scales may be found. It bears some resemblance to the indusiate D. glabra. The much larger, finely dissected D. tetrapinnata differs from D. unidentata by its very fine dissection, larger size, and more limited distribution.

In several publications and unpublished checklists, D. unidentata was reported as D. acutidens, a name Christensen published in 1905 in response to the transfer of Phegopteris spinulosa Hillebr. to Dryopteris. When the species was transferred to Dryopteris, the name Dryopteris spinulosa could not be used because it had already been assigned to an-other species. The type specimen of P. spinulosa/D. acutidens matches the species concept of D. unidentata, which Hooker and Amott originally described in 1832 as Polypodium unidentatum. Because in botanical nomenclature the law of priority requires that the earliest-published specific epithet be applied to the taxon in question, in this case unidentata is the correctly applied name.