Humidicutis poilena Desjardin et Hemmes, sp. nov.

Pileus 12-20 mm latus, late convexus vel obtuso-conicus, dein late conicocampanulatus, haud striatus, glaber, subhygrophanus, siccus, croceus. Lamellae late adnatae vel arcuatae, distantes, luteae vel alboluteae. Stipes 25-45 X 2-4 mm, aequalis, fistulosus, glaber, siccus, croceus vel pallide aurantiacus. Odor nullus. Sporae (7.0-)7.5-9.0(-9.6) X 4.8-6.0(-6.5) µm, late ellipsoideae, haud constrictae. Basidia 42-60 X 6.0-7.7 µm, tetrasporigera. Cheilocystidia et pleurocystidia nulla, lamellarum acies fertilis. Pileipellis cutiformis, c. 100 µm profundus, ex hyphis 3-8 µm latis, cylindraceis, haud gelatinosis, cellulae terminales cylindraceae, 40-120 X 4 9.5(-14) µm. Lamellarum mediostratum subregularis, ex cellulis brevibus, inflatis vel cylindraceis, 25-80 X 4-20(-24) µm, laterostrati irregularis, ex hyphis 3-10 µm latis. Stipitepellis cutiformis. Fibulae typi medallionei ad basidia praesentes, ceterum desunt. Holotypus: Hawai`i, Saddle Rd. at 19 mi. kipuka, 14 Oct. 1995, D. E. Hemmes 917 (SFSU; Isotypus: BISH).

Pileus (Fig. 34) 12-20 mm diam, broadly convex to obtusely conical when young, expanding with maturation to broadly conical or campanulate, finally broadly campanulate; margin decurved, non-striate; surface glabrous, moist to dry, subhygrophanous; deep yellow (4A7-8) overall when young, remaining so in age or fading slightly at maturity and with moisture loss to yellow (4A6), lacking orange or red tones. Context thin (0.2-0.5 mm), concolorous with pileus surface. Lamellae horizontal to ascending, broadly adnate or arcuate, often with a short decurrent tooth but never decurrent, distant with 3 series of lamellulae, moderately broad (2-3 mm); yellow (3-4A4-5), light yellow or yellowish white. Stipe 25-45 X 2-4 mm, central, terete, equal or with a slightly enlarged central region, fistulose, glabrous, dry; apex deep yellow (4A8) to light orange (5A5), base yellow or light yellow (4A3-6) to light orange. Odor not distinctive; taste not recorded.
Basidiospores (Fig. 35) (7.0-)7.5-9.0(-9.6) X 4.8-6.0(-6.5) µm [range of means = 8.3-8.7 X 5.4-5.7 µm, mean of means = 8.5 ± 0.3 X 5.6 ± 0.2 µm, Q = 1.3-1.7, range of Q means = 1.52, mean of Q means = 1.52 ± 0.0, n = 25 spores per 2 collections], broadly ellipsoid, not constricted, smooth, hyaline, inamyloid, thin-walled. Basidia (Fig. 36) 42-60 X 6.0-7.7 µm, 4-spored, subcylinrical to subclavate, with large medallion clamps from which other basidia proliferate. Basidioles subclavate. Hymenial cystidia and pseudocystidia absent. Pileipellis a cutis up to 100 µm thick; hyphae 3-8 µm diam, repent, cylindrical, not constricted at septa, nongelatinous, hyaline to pale yellowish, unclamped; terminal cells 40-120 X 4-9.5(-14) µm, cylindrical to subclavate. Pileus trama composed of hyphae 28-120 X 4-20 µm, cylindrical to inflated or fusoid, hyaline, nongelatinous, unclamped. Hymenophoral trama composed of a narrow mediostratum and a broad lateral stratum; mediostratum subregular, hyphae 25-80 X 4-20(-24) µm, cylindrical to inflated or fusoid, constricted at septa, nongelatinous, unclamped; lateral stratum irregular (interwoven), hyphae 3-10 µm diam, cylindrical to sinuous, not constricted at septa, nongelatinous, unclamped. Stipitipellis a cutis similar to the pileipellis; caulocystidia absent. Clamp connections present at base of basidia, absent elsewhere.
Habit, habitat and distribution. Solitary to scattered among mosses on fallen hapu`u logs (Cibotium spp.) in Montane Mesic Forest (Ohi`a/Hapu`u Forest). November. Hawai`i.
Specimens Examined. U.S.A. HAWAII: Hawai`i, Saddle Rd. at 19 mi. kipuka, 14 Oct. 1995, DEH 917 (Holotype); same location, 28 Nov. 1995, DEH 931.
Etymology. "po`ilena": po`i = cap; lena = yellowish in color - Hawaiian for yellowish pileus.
Commentary. Humidicutis poilena is characterized by entirely yellow basidiomes with obtusely conical to campanulate, dry pileus, broad arcuate lamellae, a narrow, dry stipe, broadly ellipsoid, non-constricted basidiospores, and absence of clamp connections except at the base of basidia. The species is know at present from a single montane ohi`a - hapu`u kipuka on the island of Hawai`i, and is considered by us to represent a native Hawaiian species, possibly endemic. In the field, H. poilena might be confused with the common Hygrocybe lamalama which grows also in endemic montane ohi`a - hapu`u forests. The latter species differs, however, in forming a more orange, convex to convex-depressed pileus, constricted basidiospores, shorter and broader basidia (31-45 X 7-9 µm), and forms clamp connections in all tissues. Humidicutis poilena differs from H. peleae by the features compared in the key.
The hymenophoral trama of Humidicutis poilena is unusual among hygrophoroid taxa. It is formed from a distinct but narrow subregular mediostratum of inflated, short-celled hyphae surrounded by a relatively broad irregular (interwoven) lateral stratum of cylindrical to sinuous hyphae, but is not divergent (bilateral) as in Hygrophorus species. The mediostratum is similar in construction to the hymenophoral trama of Humidicutis species, while the lateral stratum is more reminiscent of the hymenophoral trama of Hygrocybe subgen. Cuphophyllus Donk (= Camarophyllus Kummer sensu auct.) species. We place H. poilena in the genus Humidicutis and not in Hygrocybe subgen. Cuphophyllus because of it non-decurrent lamellae, and the absence of clamp connections in all tissues except at the base of basidia. Moreover, the unusual, large medallion clamps at the base of basidia from which other basidia often proliferate is a typical feature of Humidicutis species (e.g., H. marginata (Pk.) Singer, H. conspicua (Horak) Horak, H. peleae Desjardin & Hemmes).

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