Synonym(s):Asplenium caudatum sensu Hillebr., non G. Forst.; A. contiguum var.fi/ifonne (Kaulf.) Hillebr.; A. contiguum var. laciniatum Hillebr.; A. filiforme Kaulf.; A. knudsenii Hillebr.

Endemic

Latin contiguus, bordering, near, adjoining, probably referring to the sori that are contiguous and parallel to the midvein.

Plants small to medium-sized, usually epiphytic. Rhizomes creeping, 4-7 mm diam., covered with tan to brown, linear-lanceolate scales. Fronds 13-80 em long. Stipes slender, 1.5-2.5 mm wide, brown, glossy, hairs (in-cluding glandular hairs) occasional to many, scales only at base, linear-lanceolate, often falcate, tan to brown, never proliferous. Blades 1-pinnate, variable, oblong-lanceolate, nar-rowed slightly at base, dark green, glossy, chartaceous, glabrous except for scattered fibrils; rachises nearly glabrous to well covered with glandular hairs. Pinnae 15-35 pairs, short-stalked, attached at proximal margins of bases, notched or incised, dentate or serrate (proximal 1/4-1/2 of lower margin often entire), not lobed (occasionally cut into narrow lobes), 1.5-12 x 0.3-1.2 em, lower margins perpendicular to rachises, upper basal margins parallel with rachises or angling slightly, tips long, acuminate, narrow. Veins at first lying near costae, then curving outward at middle of pinnae and ending in marginal teeth. Sori in rows parallel to and nearly contiguous with costae, and often with each other, bilaterally, overlapping in older pinnae, 6-16 mm long, extending only 1/4-1/5 distance to margin, never more than halfway to margin, a few sori near distal portion of pinnae bases arising at angles of 20-30°. Indusia narrow.

Common and widespread epiphyte, occa-sionally terrestrial, in mesic to wet forests, 335-1,675 m, all major islands. There are two varieties, one glabrous or nearly so and one heavily covered with glandular hairs. Plants intermediate between the two varieties are found.
A characteristic of this species is the pres-ence of very small, fully fertile fronds within clusters of larger, more mature fronds. Although the written descriptions and all pub-lished illustrations of A. contiguum state or illustrate that the sori are close to and parallel with the costae, there are plants otherwise typical of A. contiguum having sori that spread away from the costae and resemble the pattern on A. polyodon. Previous authors have noticed the difficulty of separating some fronds of A. contiguum from those of A. poly-odon, and there are collections of ambig-uous fronds at the Bishop Museum that have abortive spores, suggesting a sterile hybrid between the two taxa. The relationship be-tween these two taxa needs further study.

A larger terrestrial plant found in the Koke 'e area of Kaua 'i may represent a variety of A. contiguum or a new species.

Asplenium contiguum, a 1-pinnate fern, may be distinguished by its usually epi-phytic habit; narrow, long-lanceolate, acute-tipped pinnae; tendency for a frond cluster to produce very small, fully fertile fronds; and sori nearly contiguous with midribs and arranged close and parallel to both sides of the midribs.