Hygrocybe mexicana Singer (Sydowia 12: 225. 1958.) f. defibulata Desjardin et Hemmes, forma nov.
A typo differt fibulis nullis et basidiis bisporigeris pro parte maxima. Holotypus: Hawai`i, Hilo, 333 Kalili St., 21 Sept. 1994, D. E. Hemmes 576 (SFSU; Isotypus: BISH).
Pileus (Fig. 6) 5-10 mm diam, at first convex, soon plano-convex with a central depression, in age plano-umbilicate; margin pellucid-striate to striate, even to slightly wavy in age; surface moist to dry, glabrous, subhygrophanous; deep red (10-11C8) overall when young, remaining so on the disc or fading to pink (umbilicus dingy pinkish white), margin deep red throughout maturation with a very narrow ring of yellowish orange at the edge, or fading between striae to red or reddish orange, old basidiomes with a reddish brown tone (11E8). Context very thin, concolorous with the pileus. Lamellae horizontal, broadly adnate, sometimes with a decurrent tooth, rarely subdecurrent, distant with 2 series of lamellulae, triangular, broad (1-2 mm); at first orangish white to pinkish white (6-8A3-4), in age orangish red to red (8-9A5-6) with paler edges (yellowish pink). Stipe 4-10 X 0.5-1 mm, central, terete, equal or with slightly flared apex, glabrous, dry; apex deep red (10-11C8), gradually paler downward to red or orangish red (8-9A5-7). Odor not distinctive; taste not recorded.
Basidiospores (Fig. 7) (7.7-)8.0-10.5(-12.0) X (5.0-)6.0-7.5(-8.5) µm [range of means = 9.3-9.4 X 6.5-6.6 µm, mean of means = 9.4 ± 0.1 X 6.6 ± 0.02 µm, Q = 1.1-1.7, range of Q means = 1.41-1.44, mean of Q means = 1.42 ± 0.02, n = 25 spores per 3 collections], variable in shape and size, broadly ellipsoid to ovoid, not constricted, smooth, hyaline, inamyloid, thin-walled. Basidia (Fig. 8) monomorphic, (22-)27-35 X 7.5-9.5 µm, predominantly 2-spored, rarely 1-, 3- and 4-spored, clavate, unclamped. Basidioles clavate. Hymenial cystidia and pseudocystidia absent. Pileipellis a cutis to a slight ixocutis; hyphae 2.5-8 µm diam, repent, radially arranged, cylindrical, not constricted at the septa, hyaline, unclamped; terminal cells repent, 50-100 X 4.5-8 µm, cylindrical to subclavate. Pileus trama little differentiated from pileipellis; hyphae 4-20 µm diam, nongelatinous. Hymenophoral trama regular; hyphae >500 X 8-24 µm, elongate-fusoid, tapered towards both ends, nongelatinous, hyaline, unclamped. Stipitipellis a cutis similar to the pileipellis; caulocystidia absent. Clamp connections absent.
Habit, habitat and distribution. Solitary in moss, soil or cinder rock, rarely on moss covered rotten wood, in Lowland Alien Forest dominated by strawberry guava (Psidium cattleianum Sabine), or in nursery pots in gardens. January, August-October. Hawai`i.
Specimens Examined. U.S.A. HAWAII: Hawai`i, Hilo, 333 Kalili St., 21 Sept. 1994, DEH 576 (Holotype); same location, 10 Jan. 1992, DED 5476; same location, 9 Aug. 1994, DEH 528; Hawai`i, Hilo, Mike Au's Farm, 10 Oct. 1995, DEH 896.
Commentary. Hygrocybe mexicana is characterized by a very small, plano-umbilicate, dry, deep red pileus, distant, broadly adnate, orangish red lamellae, a small, narrow, dry, deep red stipe, and relatively large basidiospores. Form defibulata differs from f. mexicana in lacking clamp connections throughout basidiomes and in producing primarily bisporic basidia. Our concept of the species is based on the protologue (Singer, 1958). The very long (>500 µm), elongate-fusoid hyphae of the hymenophoral trama and the relatively short and broad basidia (Q < 4) suggest that H. mexicana belongs in subgen. Hygrocybe, although the broadly adnate lamellae and pileus that does not split readily at maturity suggest affinities with subgen. Pseudohygrocybe.
The protologues of Hygrocybe mexicana (Singer, 1958) and Hydrocybe rosea Murrill (described from Jamaica; Murrill, 1911) are very similar, differing significantly only in basidiospore size. Basidiospores of H. rosea were reported as 10-13 X 7-9 µm (8-13 X 6-9 µm according to a type analysis by Hesler and Smith, 1963), while those of H. mexicana were reported as 7-9.5 X 4-7 µm. Unfortunately, there is insufficient material left in the holotype specimen of H. rosea (NY!) for microscopic analysis and we must rely on the incomplete micromorphological data provided by Murrill (1911), and Hesler and Smith (1963). Further specimens of these taxa from Jamaica and Mexico should provide data to determine whether the variation in basidiospore size reported is taxonomically significant, or whether the two entities are conspecific.
Hygrocybe mexicana f. defibulata is easily recognized in the Hawaiian Islands because of it small size, deep red pigments, lack of gelatinous tissues and clamp connections, and occurrence in lowland alien forests.
