Hygrocybe constrictospora Arnolds, Persoonia 12: 476. 1985.

Selected Descriptions and Icones. Arnolds (1977: 250-253; 1990: 94-95); Boertmann (1995: 100-101).

Pileus (Fig. 41) 15-27 mm diam, convex when young, becoming broadly convex to plano convex with slightly depressed disc and decurved margin in age; surface glabrous, dry to moist or greasy (not viscid), non-striate or short-pellucid-striate when moist, hygrophanous; deep red (10C6-8) overall when young or with a narrow yellowish orange ring at the margin, fading at maturity on the disc to red (9B-C8), reddish orange (8B8) or orange (6A6), and remaining deep red (10B-C8) on the margin or more commonly fading to orange or yellowish orange on the margin in age. Lamellae horizontal, adnate to emarginate with a short decurrent tooth, distant with 2-3 series of lamellulae, moderately broad (2-4 mm), deep orange (6A8) to orange (5-6A5-6; 6B7) with a yellowish orange to yellow margin. Stipe 15-45 X 3-5 mm, central, terete, equal above an enlarged base or gradually narrowed downward, fistulose, glabrous, dry; apex deep red (10C8) to reddish orange (8B8) or yellow (4A6), grading downwards to orange (6A6-8; 5A7) or yellow (4A6) above a yellow to yellowish white base, occasionally when young with a pure yellow stipe. Odor and taste not distinctive.
Basidiospores (Fig. 42) (6.5)7.0-9.0(-10.0) X 3.5-5.0 µm [range of means = 7.1-8.2 X 3.9-4.7 µm, mean of means = 7.8 ± 0.4 X 4.4 ± 0.4 µm, Q = 1.5-2.3, range of Q means = 1.7-2.0, mean of Q means = 1.8 ± 0.1, n = 20-25 spores per 5 collections], elongate-ellipsoid to narrowly pyriform, many broadened at distal end in face view, 70%-90% constricted, smooth, hyaline, inamyloid, thin-walled. Basidia (Fig. 43) (30-)40-50 X 6.0-7.7 µm, 4-spored, subclavate, clamped. Basidioles subclavate. Hymenial cystidia and pseudocystidia absent. Pileipellis a cutis 25-40 µm thick; hyphae 3-7 µm diam, repent, slightly interwoven but radially arranged, cylindrical, not constricted at septa (rarely slightly constricted), nongelatinous, hyaline, clamped; terminal cells 24-56 X 4-10 µm, repent to suberect, cylindrical to clavate, seldom in small suberect clusters. Pileus trama composed of hyphae 24-80 X 4-16(-28) µm, cylindrical to inflated, constricted at septa, nongelatinous, hyaline, clamped. Hymenophoral trama subregular; hyphae 13-65(-100) X 4-16(-20) µm, cylindrical to slightly inflated, nongelatinous, hyaline, thin-walled, clamped; with scattered refractive oleiferous hyphae 3.0-6.5 µm diam interspersed. Stipitipellis a cutis similar to the pileipellis, nongelatinous; caulocystidia absent. Clamp connections present in all tissues.
Habit, habitat and distribution. Solitary in soil or among mosses, sometimes on fallen hapu`u logs in Montane Wet Forest (Ohi`a/Hapu`u Forest) and Montane Mesic Forest (Ohi`a Forest). October to February. 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', 11 Oct. 1994, DEH 624; Hawai`i, Saddle Rd. at 18.5 mi kipuka, N 19°40.691', W 155°19.425', 22 Feb. 1994, DEH 427; Hawai`i, Saddle Rd. at 18.5 mi kipuka, 1000 steps site, 31 Oct. 1995, DEH 908; same location, 14 Nov. 1995, DEH 914; Hawai`i, Saddle Rd. at 19 mi kipuka, N 19°40.550', W 155°20.180', 14 Nov. 1995, DEH 915; same location, 28 Nov. 1995, DEH 929; same location, 20 Aug. 1996, DED 6531.
Commentary. Features of the Hawaiian specimen are indistinguishable from those of the European H. constrictospora as described by Arnolds (1977, 1990) and Boertmann (1995), although the Hawaiian basidiomes are not associated with grasslands or Salix. The species is characterized by the following features: deep red to reddish orange, greasy, glabrous pileus; broadly adnate to emarginate, orange lamellae; a red to reddish orange or yellow, dry stipe; relatively small, constricted basidiospores; long and narrow basidia; pileipellis and stipitipellis a cutis; and subregular hymenophoral trama composed of short, broad cells. In combination these features dictate placement in subgen. Pseudohygrocybe M. Bon, sect. Coccineae Fay., subsect. Coccineae (Bataille) Singer. In the Hawaiian Islands, H. constrictospora is known at present only from native montane ohi`a - hapu`u forests on Hawai`i and we consider it an indigenous species. In these forests, weathered specimens of H. constrictospora might be confused with H. lamalama, but the latter differs in never developing deep red tones on pileus or stipe, and in having broader basidiospores (range of w = 5.2-5.3 µm, mean Q = 1.5).

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