Hygrocybe hapuuae Desjardin et Hemmes, sp. nov.

Pileus 5-12 mm latus, obtusatoconicus vel convexus, dein plano-convexus, striatus, glaber, viscidus, ad discum aurantiacus vel pallide aurantiacus, marginem versus alboaurantiacus vel alboluteus. Lamellae late vel anguste adnatae, distantes, albae. Stipes 15-28 X 0.75-1.0 mm, aequalis, glaber, viscidus, alboluteus. Odor nullus. Sporae (5.7-)6.0-8.0(-8.5) X (3.5-)4.0-5.0 µm, ellipsoideae, haud constrictae. Basidia 22-37 X (5.7-)6.5-9.0 µm, tetrasporigera. Cheilocystidia et pleurocystidia nulla, lamellarum acies fertilis. Pileipellis ixocutiformis, ex hyphis 2.0-6.5(-8.0) µm latis, cylindraceis, interdum erectis, subgelatinosis. Lamellarum trama regularis vel subregularis, ex cellulis brevibus, inflatis vel cylindraceis, 50-160 X 4-24(-32) µm. Stipitepellis ixocutiformis. Fibulae praesentes. Holotypus: Hawai`i, Natural Area Reserve System, Pu`u Maka`ala, 7 Jun. 1994, D. E. Hemmes 463 (SFSU; Isotypus: BISH).

Basidiomes (Fig. 28) mycenoid. Pileus 5-12 mm diam, obtusely conic or convex, expanding to broadly convex or nearly plano-convex in age; margin decurved, even to crenulate, pellucid-striate to striate; surface glabrous, subviscid to viscid; disc orange (5C8) to light orange (5A4-5), margin light orange (5A3-4) to light yellow (4A3-4), fading overall at maturity with the margin reaching pale orange white (5A2) to nearly white. Context thin (<1 mm), concolorous with pileus surface. Lamellae ascending, ranging from narrowly adnate to broadly adnate or arcuate with a subdecurrent tooth, distant with 1-3 series of lamellulae, narrow to moderately broad (0.5 1.5 mm), white. Stipe 15-28 X 0.75-1.0 mm, central, terete, equal, glabrous, shiny, viscid (but not glutinous); light yellow (4A5) overall. Odor not distinctive; taste not recorded.
Basidiospores (Fig. 29) (5.7-)6.0-8.0(-8.5) X (3.5-)4.0-5.0 µm [range of means = 6.2-7.5 X 3.9-4.7 µm, mean of means = 6.9 ± 0.7 X 4.4 ± 0.4 µm, Q = 1.4-1.8, range of Q means = 1.5-1.6, mean od Q means = 1.56 ± 0.05, n = 25-30 spores per 3 collections], ellipsoid, not constricted, with a prominent broad obtuse hilar appendix, hyaline, inamyloid, smooth, thin-walled. Basidia (Fig. 30) 22-37 X (5.7-)6.5-9.0 µm, 4-spored, rarely 2-spored, clavate, clamped. Basidioles subclavate to clavate. Hymenial cystidia and pseudocystidia absent. Pileipellis a loosely interwoven cutis to an ixocutis, nearly an ixotrichodermium in some basidiomes; hyphae 2.0-6.5(-8.0) µm diam, repent to erect, cylindrical, not constricted at the septa, non-diverticulate, nonincrusted, nongelatinous or more commonly weakly gelatinous, hyaline, inamyloid, predominantly unclamped, clamps rare but many septa with false clamps; terminal cells 16-68 X 4.0-6.5(-8.0) µm, repent to erect, cylindrical to subclavate, obtuse. Pileus trama composed of hyphae 30-120 X 4-20(-24) µm, cylindrical to inflated, nongelatinous, inamyloid, unclamped; hypodermium absent. Hymenophoral trama regular to subregular; hyphae 50-160 X 4-24(-32) µm, cylindrical to inflated, some fusoid, hyaline, inamyloid, nongelatinous; with scattered oleiferous hyphae. Stipe tissue monomitic; hyphae 1.5 9.0 µm diam, cylindrical, parallel, hyaline to pale yellow, nongelatinous, unclamped. Stipitipellis an ixocutis like the pileipellis but with hyphae typically narrower, 1.5-4.0 µm diam, hyaline to pale yellow, clamped but not at every septum
Habit, habitat and distribution. Scattered on aerial senescent fronds or moss-covered fallen logs of hapu`u (Cibotium spp.) in Montane Wet Forest (Ohi`a/Hapu`u Forest). June to August. Hawai`i.
Specimens Examined. U.S.A. HAWAII: Hawai`i, Natural Area Reserve System, Pu`u Maka`ala, N 19°29.072', W 155°16.140', 7 Jun. 1994, DEH 463 (Holotype); same location, 27 June 1995, DEH 820; same location, 24 July 1995, DEH 856; same location, 10 July 1996, DEH 1158; same location, 21 Aug. 1996, DED 6547.
Etymology. "hapu`u" - Hawaiian name for the endemic tree fern genus Cibotium.
Commentary. Hygrocybe hapuuae is characterized by the following features: a small mycenoid stature; light orange, conic to convex, striate, subviscid to viscid pileus; distant, white, narrow, arcuate lamellae; narrow, viscid, yellow stipe; a gelatinized pileipellis and stipitipellis; and the absence of hymenial cystidia and caulocystidia. The species belongs in subgen. Pseudohygrocybe M. Bon, sect. Glutinosae Kühner (= Gliophorus Herink), subsect. Insipidae (Henrink) M. Bon, although basidiomes are more reminiscent of members of Mycena sects. Adonideae (Fr.) Quél. (e.g., M. ochrogaleata Favre and M. flavoalba (Fr.) Quél.) and Hygrocyboideae (e.g., M. epipterygia (Scop.: Fr.) S. F. Gray). Hygrocybe hapuuae appears to be closely allied with several non-viscid taxa, viz., H. luteo-omphaloides Norvell, Redhead & Ammirati (1994) (∫ Omphalia occidentalis A. H. Smith (1941)) and Hygrophorus mycenoides A. H. Smith & Hesler (1942). All three species share the mycenoid habit, pileus and stipe coloration, and scattered clamp connections. Hygrocybe luteo-omphaloides differs, however, in having a lemon yellow, non-striate, moist (not viscid) pileus, amber yellow and long-decurrent broad lamellae, a non-viscid stipe and slightly longer basidiospores (6.5-9.5(-10) µm in length; fide Smith, 1941; Bigelow, 1970). Hygrophorus mycenoides differs in having a moist to lubricous (not viscid) pileus, bright yellow lamellae, a non-viscid stipe, abundant subcylindrical cheilocystidia, and narrower basidia (4.5-6.0 µm broad) and basidiospores (2.5-3.5 µm diam; fide Smith and Hesler, 1942; Hesler and Smith, 1963).
We first thought that H. hapuuae might represent the long forgotten Omphalia kewense Massee, described from material collected on dead rhizomes in the Filmy Fern House at Kew Gardens, England (Massee, 1913). No herbarium material remains of this species (Pegler, pers. comm.) and the taxon is known only from the protologue. Massee's (1913) illustration shows mycenoid basidiomes with "deeply grooved, elongated, cylindric-campanulate pileus" and very broad subdecurrent lamellae. In addition, he described the pileus as colored "ochraceus dein albidus" and the stipe as "pallidus". Although these features are somewhat similar to those of H. hapuuae, the conic to convex, light orange pileus with narrow arcuate lamellae and yellow stipe of H. hapuuae are clearly distinct.
Basidiome production of H. hapuuae on aerial portions of senescent tree fern fronds is an unusual feature in Hygrocybe. Known at present from a single population associated with endemic tree ferns in a native Montane Wet Forest, we consider H. hapuuae to represent a native species, possibly endemic.

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