Agaricales of the Hawaiian Islands

Key to Hawaiian Species of Rhodocollybia and Gymnopus

The taxonomic boundaries of the common litter-decomposing genus Collybia have been recently re-evaluated (Antonín et al., 1997). What was once considered as a single genus, is now accepted as three distinct genera: Collybia sensu stricto, limited to C. tuberosa (Bull.: Fr.) P. Kumm. and allies [= Microcollybia sensu Lennox (1979)]; Rhodocollybia Singer, for species belonging to Collybia subgenus Rhodocollybia (Singer) Halling (see Halling, 1983); and the bulk of Collybia sensu lato belonging to Gymnopus (Pers.) Roussel. Prior to the data presented herein, no species of Collybia sensu lato had been reported from the Hawaiian Islands. Extensive fieldwork over the past five years on six of the eight major islands in the Hawaiian Archipelago yielded four species of Collybia sensu lato, two from montane native forests and two from lowland alien forests. All four species are quite common in their respective habitats.

In the descriptions that follow, color terms and notations are from Kornerup and Wanscher (1978); spore statistics include: the range of spore means, the mean of spore means (± SD); Q, the quotient of spore length and spore width in any one spore, indicated as a range of variation in n spores measured; the range of mean Q values; the mean of Q mean values. All specimens are deposited in SFSU unless specified otherwise. Frequently cited collectors are abbreviated as follows: D. E. Desjardin (DED), D. E. Hemmes (DEH).

Data presented in the following artificial key pertain strictly to Hawaiian populations; ecological features may not apply elsewhere in the geographical range of the introduced species.

1. Pileus 20-80 mm diam with context 2-10 mm thick; stipe 5-20 mm diam at the base.......... 2

1. Pileus 8-30 mm diam with context <1 mm thick; stipe 1-3 mm diam at the base.......... 3

2. Pileus campanulate, typically with a broad, low umbo, glabrous, non-striate; lamellae extremely crowded, narrow (1-4 mm), anastomosing and labyrinthine near the stipe, usually with a circumsessile constriction near the stipe; taste bitter; basidiospores 5.5-7.0 X 3.5-4.5 µm; cheilocystidia contorted-cylindrical to sinuous, 3-6 µm diam; basidiomes a common component of native forests associated with ohi`a, hapu`u, koa and other endemic plants.......... Rhodocollybia laulaha

2. Pileus convex to broadly convex, seldom umbonate, glabrous to radially appressed-fibrillose and streaked, striate; lamellae close to subdistant, moderately broad to broad (3-7 mm), not anastomosing nor labyrinthine, not constricted near the stipe; taste mild to slightly acrid; basidiospores 8-10 X 4.2-5.0 µm; cheilocystidia versiform but often clavate, 5--10 µm diam; basidiomes a common component of Coastal Casuarina Forests and horticultural areas, never observed in native forests.......... Gymnopus luxurians

3. Pileus obtusely conic to broadly convex or campanulate, often with a small umbo, not umbilicate, strongly rugulose-striate or corrugate-sulcate; lamellae adnate to shallowly adnexed, subdistant to distant; basidiospore width 4.5-5.2 µm; cheilocystidia 25-80 µm long, unlobed, often in chains of 2-3 cells; pileipellis hyphae non-diverticulate; pileocystidia scattered, cylindrical to sinuous, clavate, ventricose or sphaeropedunculate, non-diverticulate; caulocystidia 60-120 X 2.5-10.0 µm, often in clusters of 2-10 cells, gradually tapered to a narrower apex; in montane forests on woody debris of ohi`a, koa and karakanut or rarely on pine debris.......... Gymnopus subpruinosus

3. Pileus broadly convex to plano-convex, umbilicate, pellucid-striate, rarely slightly rugulose striate; lamellae adnate to subdecurrent, close to crowded; basidiospore width 3.5--4.2 µm; cheilocystidia 22--42 µm long, often lobed, not in chains; pileipellis hyphae with broad diverticula; pileocystidia undifferentiated; caulocystidia 16-64 X 3-5 µm, single, diam consistent over the entire length of the cell; in lowland forests on leaf mulch under Casuarina or mixed alien plants, or on woodchips in horticultural areas.......... Gymnopus menehune

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