Pileus (7-)10-25 mm latus, semiglobatus vel convexus, dein late convexus vel planoconvexus, ad discum depressus, haud striatus, glaber, hygrophanus, siccus, citrinus vel croceus, interdum in disco aurantiacus et marginem croceus, dein pallide citrinus. Lamellae decurrentes, distantes, angustae, raro intervenosae, pallide alboluteae vel luteae. Stipes 20-55 X 2 4 mm, aequalis, solidus, glaber vel minute pruinosus, siccus, citrinus vel croceus. Odor et sapor nulli. Sporae 7.0-10.8(-12.2) X 5.4-7.0(-9.0) µm, late ellipsoideae vel ovoideae, haud constrictae. Basidia 41-56 X (7.0-)8.0-10.0(-12.5) µm, tetrasporigera, pro parte 2-, vel 3-sporigera. Cheilocystidia et pleurocystidia nulla; lamellarum acies fertilis. Pileipellis cutiformis, ex hyphis (6-)8-18 µm latis, cylindraceis, ad septas constrictis, haud gelatinosis; cellulis terminalibus cylindraceis vel clavatis, 28-100(-184) X 8-25(-28) µm, interdum erectis. Lamellarum trama subregularis, ex cellulis brevibus, inflatis vel cylindraceis, 30-140 X 4-16(-20) µm. Stipitepellis cutiformis. Caulocystidia cylindriformia, 16-64 X (4.0-)6.5-13.0 µm. Fibulae praesentes. Holotypus: Moloka`i, Kamakou Forest Preserve, Hanalilolilo Trail, 9 Jan. 1995, D. E. Hemmes 714 (SFSU; Isotypus: BISH).
Pileus (Fig. 44) (7-)10-25 mm diam, hemispheric to convex when young, expanding with age to broadly convex or plano-convex, often with a shallow central depression; margin incurved throughout maturation, seldom lobed, non-striate; surface moist to dry, hygrophanous, typically glabrous overall (disc always glabrous) or seldom with the margin becoming slightly scurfy in age; when young typically deep yellow (3-4A6-8) overall or seldom orange (5-6A5-7) with a deep yellow margin, remaining deep yellow overall or with a hint of orange on the disc and deep yellow on the margin in age, fading overall to light yellow (3-4A5) with moisture loss, lacking red tones throughout development; basidiomes deep yellow, yellow or cream overall when dried. Context 0.5-2.0 mm thick, watery-concolorous with pileus surface. Lamellae decurrent to deeply decurrent, distant with 1-3 series of lamellulae, narrow to moderately broad (1-3 mm), concave, seldom forked, rarely intervenose near pileus margin; white to pale yellowish white (4A2), pale orange white (5A2) or cream (4A3) when young, remaining so at maturity or becoming yellow (4A4-6). Stipe 20-55 X 2-4 mm, central to slightly eccentric, terete or seldom compressed, equal or seldom with enlarged apex (up to 5-7 mm diam), solid to stuffed, dull, moist to dry, glabrous overall or with minutely pruinose apex; deep yellow (3-4A6-8) to yellow (4A5) overall or sometimes with orange (5A5-6) tones, never with red tones; stipe context yellowish white to yellow. Odor and taste not distinctive.
Basidiospores (Fig. 45) 7.0-10.8(-12.2) X 5.4-7.0(-9.0) µm [range of means = 8.1-9.8 X 6.0-6.9 µm, mean of means = 8.7 ± 0.7 X 6.2 ± 0.4 µm, Q = 1.2-1.6, range of Q means = 1.36-1.45, mean of Q means = 1.4 ± 0.04, n = 25-30 spores per 5 collections], broadly ellipsoid to ovoid, not constricted, smooth, hyaline, inamyloid, thin-walled. Basidia (Fig. 46) monomorphic, 41-56 X (7.0-)8.0-10.0(-12.5) µm, predominantly 4-spored, sometimes 2-, or 3-spored, clavate, clamped. Basidioles clavate. Hymenial cystidia and pseudocystidia absent. Pileipellis (Fig. 47) a cutis, sometimes with scattered clusters of suberect (ca 30°-45°) or rarely erect terminal cells; hyphae (6-)8-18 µm diam, cylindrical, constricted at septa, hyaline to pale yellow, nongelatinous, clamped; terminal cells 28-100(-184) X 8-25(-28) µm, cylindrical to clavate, typically repent but near the pileus margin sometimes forming suberect clusters (scurfy pileus surface). Pileus trama undifferentiated from pileipellis. Hymenophoral trama subregular; hyphae 30-140 X 4-16(-20) µm, cylindrical to inflated, hyaline, nongelatinous, clamped; hyaline refrigent crystals absent. Stipitipellis a cutis with scattered to dense, suberect to erect caulocystidia; hyphae 4-9 µm diam, cylindrical, hyaline to pale yellow, nongelatinous, clamped. Stipititrama hyphae 72-145 X 5-12 µm. Caulocystidia (Fig. 48) 16-64 X (4.0-)6.5 13.0 µm, cylindrical, clavate or irregular in outline, often curved, hyaline. Clamp connections present in all tissues.
Habit, habitat and distribution. Scattered to gregarious in soil and among mosses in Montane Wet Forest (Ohi`a/Hapu`u Forest), or under Monterey Cypress (Cupressus macrocarpa) and ohi`a in introduced cypress forest invading an adjacent Montane Wet Forest. All months. Hawai`i, Moloka`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', 25 May 1993, DED 5680; same location, 2 Oct. 1993, DEH 315; same location, 29 Mar. 1994, DEH 444; same location, 26 Sept. 1994, DEH 583 & 590; same location, 11 Oct. 1994, DEH 623; Hawai`i, Hawai`i Volcanoes National Park, Thurston Lava Tube, 22 Sept. 1995, DEH 850; same location, 10 July 1996, DEH 1159; same location, 21 Aug. 1996, DED 6543. Moloka`i, Kamakou Forest Preserve (The Nature Conservancy Hawai`i), Kamoku Flats, N 21°07.101', W 156°55.122', 9 Jan. 1995, DED 6217; Moloka`i, Kamakou Forest Preserve, Hanalilolilo Trail, N 21°07.554', W 156°54.882', 9 Jan. 1995, DEH 714 (Holotype); same location, 12 Jan. 1996, DED 6400.
Etymology. "pua`ena" - Hawaiian for radiance, referring to the bright yellow pigmentation.
Commentary.Hygrocybe puaena is characterized by the following features: a convex to plano-convex, yellow, dry pileus; deeply decurrent, pale yellow lamellae; a dry, yellow stipe; a cutis-type pileipellis formed from very broad hyphae with repent to suberect terminal cells; broadly ellipsoid to ovoid basidiospores with mean of means = 8.7 X 6.2 µm (mean of Q mean = 1.4); and a stipitipellis with numerous caulocystidia. Hygrocybe puaena belongs in subgen. Pseudohygrocybe M. Bon, sect. Coccineae Fay., subsect. Squamulosae (Bataille) Sing., where it is most closely allied with the north temperate H. cantharellus (Schw.: Fr.) Murrill (sometimes called H. lepida Arnolds in Europe). Hygrocybe cantharellus differs from H. puaena in forming a pileus and stipe with scarlet red to flame orange pigments, a pileipellis that is for the most part a trichodermium or at least shows numerous clusters of erect terminal cells (i.e., the pileus is squamulose), a stipitipellis that lacks conspicuous caulocystidia, a stipititrama with hyphae 120-200 µm long, and in forming slightly longer and narrower basidiospores (mean of means = 9.7 X 6.0 µm, mean of Q mean = 1.6; Arnolds (1990) reports the basidiospore mean as 8-10.5 X 5-6.5 µm, range of Q mean = 1.55-1.65; Largent (1985) reports the basidiospore mean as 10.4 X 5.6, mean Q = 1.8). Borgen and Senn-Irlet (1995) have shown that the length of hyphae in the stipititrama is taxonomically important in subsect. Squamulosae. Based on this criterion, H. puaena shows affinities with H. calciphila Arnolds and H. glacialis Borgen & Senn-Irlet. The latter two species differ significantly from H. puaena in basidiome pigmentation, habitat, adnate to subdecurrent lamellae, basidiospore size, the presence of hyaline refrigent crystals in the hymenophoral trama, and the absence of caulocystidia (cf. Borgen & Senn-Irlet, 1995).
Hygrocybe puaena has been collected only in endemic montane ohi`a - hapu`u forests and is considered by us a native, possibly endemic species.
