Typification: OAHU, HAWAII, USA: Manuwai Gulch, 505 m, 6 February 2015, J. Hayward C11O (holotype HAW-F-00088).
Etymology: The specific epithet “aulu” is the Hawaiian term for Pisonia sandwicensis, the only known ectomycorrhizal host for this species.
Basidiomatacoralloid, terrestrial, arising from a white basal mat, solitary or more usually in troops, branching di- or trichotomously early in development, 1-6 times, 1-8 mm between branchings, tips cristate with bluntly acuminate apices, more rarely with blunt-rounded apices, texture cartilaginous, 5-35 mm in height, 2-20 mm across branches, sterile stipe at maturity 5-20 mm in height; entire basidiome at first creamy-white (5Y 9/2), hymenium ripening light gray (N8 to 5Y 8/2) to finally lilac-gray (10PB 6/2), minutely hispid. Context concolorous or very slightly lighter in color than hymenium, solid in immaturity, becoming hollow with irregular lacunae in the sterile stipe containing loose hyphal wefts. Odor not apparent, taste mild. Spore deposit scanty, white.
Basidiospores(6.0) 6.17-6.42-6.69 (7.3) × (7.6) 8.27-8.51-9.0 (9.2) μm, Q (1.19) 1.25-1.32-1.38 (1.48), broadly elliptical to subovoid, hyaline, unornamented, inamyloid, in immaturity with one or two large guttules with highly refractive content, at maturity almost always with a single highly refractive guttule filling most of the volume of the spore, thin-walled. Basidia cylindrical, 32-51 μm in length, 4.7-7.1 μm in diameter at base, 5.2-6.7 μm in diameter near sterigmal attachment, gloeoporous, postpartal septa occasional; rarely with clamp connection at base, with abundant oil droplets. Basidolesabundant, up to 7.8 μm in diameter, frequently with many oil droplets.Sterigmata5.8-8.2 (mean 7.4) μm long, 1.7-2.5 μm across at base, cornute, consistently 2 per basidium. Uninflated tramal hyphae 2–4 μm wide, hyaline, interwoven. Inflated tramal hyphaerare, up to 8 μm in diameter, hyaline. Rhizomorphspoorly differentiated, with hyphae 2-5 μm in diameter, with frequent H-connections. Clamp connections frequent.
Comments: This species appears to fruit more frequently than other Pisonia sandwicensis-associating fungi. It fruits abundantly February – April on Oahu. So far as we are aware, no other Clavulina species have been reported from Hawaii, simplifying identification of this species in the field. Amongst other Clavulina species, it is macromorphologically most similar to Clavulina cinerea var gracilis (Rea) Corner. Micromorphologically, it shares many features with other acystidiate, clamped Clavulina species, including uniguttulate spores and cornute sterigmata. Amongst these taxa, the rarity and relatively small size of inflated elements in the trama and the relatively small spores set this species apart. In North America and Europe, Clavulina speciesare frequently parasitized by Helminthosphaeria clavariarum. We have never observed this parasite in Hawaii.
Specimens examined: OAHU, HAWAII, USA: Manuwai Gulch, 485 m, 6 February 2015: Hayward C6O; OAHU, HAWAII, USA: Mokuleia Forest Reserve, 393 m, 5 April 2015: Hayward C17O; HAWAII ISLAND, HAWAII, USA: Manuka, 645 m, 29 May 2015: Hayward C1H; KAUAI, HAWAII, USA: Puu Ka Pele Forest Reserve, 830 m, 2 June 2015: Hayward C8K; KAUAI, HAWAII, USA: Puu Ka Pele Forest Reserve, 635 m, 2 June 2015: Hayward C11K.