Ionosporus longipes (Massee) Khmeln, Davoodian, Raspé, S.M.L. Lee & Halling, in Khmelnitsky et al., Mycol. Progr. 18(3): 444 (2019)
Pileus (3) 4.4–6 (7.3) cm broad, convex, dry, velvety, even to uneven, brown (5E4, 5F7), with decurved to slightly uplifted margin, not bruising, turning red with NH4OH. Context 5–9 mm thick, soft and spongy, white to yellowish white, no color change when exposed, red with NH4OH. Hymenophore tubulose, adnexed to adnate, light yellow (3A5, 4A3), with concolorous pores less than 1 mm broad, bruising red, sometimes with fine black discoloration, red with NH4OH. Stipe 5.5–8 (11.6) cm long, 4–7 (9) mm broad, central, equal to slightly subclavate, dry, finely (shallowly) costate to finely sublacunose or finely elongate reticulate, otherwise subpruinose, brown to dark brown (5E4, 6F3), white at the base, no color change when bruised, red with NH4OH, with white basal mycelium; interior white with chalky consistency, red with NH4OH.
Basidiospores purplish in deposit, (13) 14–19 (22) × (5) 6– 7 μm, x = 16.5 × 6.22 μm, Q = 2.7, n = 135, p = 5, ellipsoid to subfusoid, often with an obscure germ pore, smooth under light microscope, obscurely granulose pitted under Nomarski differential interference contrast optics, dextrinoid, translucent purple in KOH, obviously granulose pitted with SEM. Basidia (20) 22– 27 × 10–12 (15) μm, 4-sterigmate, short-clavate, hyaline, inamyloid. Cheilocystidia (40) 49–65 (95) × (13) 16–20 (22) μm, ventricose to subventricose to subfusoid, hyaline, inamyloid, thin-walled. Hymenophoral trama divergent (boletoid), with hyaline elements, inamyloid. Pileus trama interwoven with hyaline, thin-walled hyphae, 4–10.4 (16) μm. Pileipellis a trichodermium, composed of erect to suberect cylindrical elements, (60) 65–108 (118) × (9) 10–15 (24) μm, smooth, thin-walled, hyaline or pale brown content, inamyloid. Stipitipellis a trichodermium of caulocystidia 29–43 × 9– 15 μm, subcylindric to clavate, smooth, thin-walled, inamyloid, with brown content in KOH, subtended by longitudinally oriented, hyaline, cylindrical tramal hyphae. Clamp connections absent.
Distribution: Currently known from Singapore and peninsular Malaysia
Habit and habitat: Gregarious on soil under Dipterocarpaceae (Shorea sp.). According to Lee (2017), the species occurs in groups during the rainy season in Kepong, Malaysia, growing under various dipterocarps, including Shorea acuminata Dyer and S. macroptera Dyer.
Index fungorum number: IF827133
Notes: The long slender stipe of I. longipes is a feature noted by Massee (1909) but is not always present (, Lee 1180). However, the purple-violet discoloration of the spores when in contact with KOH solution distinguishes it from the typical features of the genera it had been placed in by previous authors. That character can also serve as an additional indicator of the placement of other epigeous species in Ionosporus and the sister clades including Borofutus, Spongiforma, and Rhodactina. While B. tristis and B. longipes were said to differ based on differences in hymenial thicknesses and spore morphology (Wolfe 1979), Corner’s (1980) closer study of the morphological features and keen observations of live material suggest little significant distinction. Closer observations of the spores of I. longipes (Lee 1180, Lee 1208) showed that a minority displayed striations, especially when mounted in Melzer’s, a feature reminiscent of Horak’s (2011) evaluation of B. tristis. The presence of obscure germ pores on some spores of both taxa supports synonymy. The contaxic relationship between the two species is strengthened when comparing SEMs of the spores of B. tristis (Hosen et al. 2013) and I. longipes, which show little to no difference in spore ornamentation. The recent specimen from Singapore, Lee 1180, had a faint but clearly deep purple spore deposit with spore size, shape, and KOH reaction strongly reminiscent of B. tristis. At this point, besides the phylogenetic inference and spore size and shape differences, the other microscopic features are reminiscent of I. australis sp. nov. described below. More collections in SE Asia are needed for critical evaluation. A Malaysian specimen (KUM 90057) that we treat as a specimen of A. longipes could not be sequenced due to highly degraded genomic DNA.
Figure 1. Scanning electron micrographs. a, b I. longipes KUM 90057 (white arrow in b pointing to germ pore).
Figure 2. Phylogram from maximum likelihood analysis of rpb2 data. Bootstrap values > 50% are shown followed by Bayesian posterior probabilities > 0.5. A B-^ indicates bootstrap value < 50%. Scale bar shows substitutions/site. Chalciporus africanus was specified as the out-group for this analysis