Solioccasus polychromus Trappe, Osmundson, Binder, Castellano, & Halling, in Trappe et al., Mycologia 105(4): 891 (2013)
Etymology: Greek, poly- (many) and -chromus (colored), “many colored”.
Basidiomata gregarious, 8–32 × 10–45 mm, subglobose to turbinate or irregularly lobed and furrowed, on larger specimens the base deeply indented; base with appressed to emergent, yellow to orange rhizomorphs up to 1.7 mm broad. Peridium continuous and pallid-pubescent in youth, dry, with age the pubescence remaining only in depressions and the peridium split in places or reduced to remnant patches to expose the gleba, where present ≤ 0.5 mm thick and sordid yellowish white to olive but orange in cross section, soon becoming moderate yellow (ISCC-NBS 87) to strong pink (ISCC-NBS 2), then deep pink (ISCC-NBS 3) mottled and streaked with light orange-yellow (ISCC-NBS 70) to moderate orange-yellow (ISCC-NBS 71) and at full maturity variously vivid orange (ISCCNBS 48), vivid orange-yellow (ISCC-NBS 66) and vivid reddish orange (ISCCNBS 70). Rhizomorphs up to 0.8 mm thick, scattered to abundant, concolorous with the peridium, emergent from the base and appressed on bottom and sides of basidiomata. Gleba rubbery-cartilaginous, with globose to elongate locules 0.1–1.5 mm broad, ivory to pale yellow in youth, soon developing the same range of colors as the peridium, with an inconspicuous to robust gray-translucent to yellow or red, dendroid, cartilaginous columella up to 1 mm broad at the base, some branches percurrent and becoming pink to orange where emerging at the basidiome surface. Spores lining the locules moderate greenish yellow (ISCC-NBS 102) in mass, becoming cinnamon to brown in patches in fully mature specimens. Odor pleasant to pungent or fungoid. Flavor not distinctive.
Spores ellipsoid to broadly ellipsoid or occasionally subangular to subfusoid or allantoid in some specimens, with a sterigma attachment 1 × 1–2 µm; (8–)10–14(–17) × (5–)6–8(–9) µm (Q = 1.4–2.6), the lower Qs predominant in some specimens, the higher Qs in others, the walls up to 0.8(–1) µm thick at maturity, appearing smooth by light microscopy or faintly roughened by Nomarski imaging but distinctly minutely roughened by SEM; light yellow in KOH and Melzer's reagent, deep blue in cotton blue. Basidia clavate, 32–40 × 7–10 µm, with 2(–4) sterigmata ± 4–6 × 1 µm. Peridium 200–300 µm thick, with a suprapellis, pellis and subpellis; suprapellis a tangled trichodermium of hyaline, obtuse hyphal tips 3–5 µm broad; pellis tightly constructed of periclinal, hyaline, highly gelatinized hyphae 2–5 µm broad; subpellis of similar but tightly interwoven hyphae. Gleba trama 100–250 µm thick, of sinuous-subparallel, hyaline, highly gelatinized hyphae 2–4 µm broad. Subhymenium of interwoven hyphae otherwise similar to those of the trama. Clamp connections lacking.
Distribution, habitat and season: Australia (Northern Territory and Queensland) and Papua New Guinea, in lowland tropical and subtropical forests with various mixtures of ectomycorrhizal Allocasuarina littoralis, Corymbia dichromophloia, C. erythrophloia, C. polycarpa, Eucalyptus pellita, E. pilularis, E. racemosa, E. tetrodonta, Leptospermum spp., Lophostemon sp. and Melaleuca spp., often in sandy soil. February, March.
Index Fungorum number: IF800825
Figure 1. Single-locus phylogram of representatives of Boletales based on maximum likelihood analysis of nuclear ribosomal large subunit DNA sequences by RAxML-HPC 7.2.8. Final GAMMAbased score of best tree = −6046.87. Bootstrap percentage values (based on 1000 bootstrap replicates) greater than 50 appear above branches. Solioccasus is strongly supported (bootstrap = 97%) as monophyletic with Bothia castanella. Athelia decipiens and Athelopsis subinconspicua were used as outgroup taxa.
Figure 2. Solioccasus polychromus basidiomata. a. Cross section showing gleba and prominent columella (co). b. Surface with appressed concolorous rhizomorphs (ar) and exposed glebal locules (gl). Scale bars = 10 mm.