Inocybe fragilissima E. Horak, Matheny & Desjardin, 2015

Horak, Egon, Matheny, P. Brandon, Desjardin, Dennis E. & Soytong, K., 2015, The genus Inocybe (Inocybaceae, Agaricales, Basidiomycota) in Thailand and Malaysia, Phytotaxa 230 (3), pp. 201-238 : 224-226

15. Inocybe fragilissima E. Horak, Matheny & Desjardin , spec. nov. Fig. 14a–h ; Pl. 5a , 8g

MycoBank MB519913

Etymology: fragilissimus (Lat.), most fragile.

Diagnosis: Basidiomes very small. Pileus 7–13 mm wide, developing a low umbo or small obtuse-conical papilla with age, surface minutely innately fibrillose, distinctive velipellis absent, margin not splitting, cinnamon brown to argillaceous brown. Lamellae adnexed to almost free, pale cinnamon when young, gradually becoming dark fuscous or dark chocolate brown. Stipe 15–25 × 1 mm, pallid or paler than the pileus, base not bulbous, upper part distinctly pruinose, lower half appressed fibrillose, cortina absent. Basidiospores 5.5–7 × 4–4.5 μm, nodulose or irregularly angled with few inconspicuous nodules. Cheilocystidia, pleurocystidia, and caulocystidia 35–60 × 10–17 μm, fusoid, walls up to 2.5 μm thick, ochre brown or yellowish. In tropical lowland forest dominated by Dipterocarpaceae , Thailand.

Holotype:— THAILAND. Chiang Mai Prov.: Hwy 1095, at 22 km marker, N19˚07‘57.0‘‘, E98˚45 ‘64.7‘‘, on soil in tropical submontane forest (dominated by Dipterocarpus ), 11 Jun. 2006, leg. D. E. Desjardin ( DED 8061 , SFSU, holotype) GenBank accession no. GQ893021, GQ892977.

Pileus 7–13 mm wide, at first convex, becoming expanded with low umbo or small obtuse-conical papilla in age, cinnamon brown to argillaceous brown (6E5–6, with pale ochre tinge), minutely innate-fibrillose all over, non-striate margin not splitting, if moist slightly viscid (covered with soil particles), soon dry, distinctive velipellis absent. Lamellae 32–40 reaching stipe, 3 (–7) lamellulae, moderately close, adnexed to almost free, up to 1.5 mm broad, narrow, at first pale cinnamon (6D4) but gradually becoming dark fuscous or dark chocolate brown; edges subfimbriate, concolorous. Stipe 15–25 × 1 mm, cylindrical, equal or gradually enlarging into base, sometimes slightly swollen; surface dry, upper portion distinctly pruinose, lower half appressed fibrillose, pallid or paler concolorous with pileus, basal tomentum absent; cortina absent; context solid, concolorous, unchanging upon exposure. Odor not distinctive or weakly acidulous to spermatic. Taste similar to odor.

Basidiospores 5.5–7 × 4–4.5 μm, nodulose or irregularly angled with few inconspicuous nodules, pale yellow-brown, germ pore absent, brown in deposit. Basidia 24–30 × 6–7 μm, 4-spored, slender clavate. Cheilocystidia 35–60 × 10–17 μm, fusoid, metuloid, with ochre brown or yellowish walls up to 2.5 μm thick at apex, occasionally also with ochre brown, plasmatic pigment, scattered crystals or resinous matter present; paracystidia 12–23 × 8–12 μm, clavate to vesiculose, hyaline, thin-walled, scattered. Pleurocystidia similar to cheilocystidia. Caulocystidia similar to cheilocystidia, often in clusters, intermixed with numerous clavate-vesiculose, hyaline cells. Pileipellis a cutis of repent, cylindrical hyphae, 3–4 μm wide, terminal cells not differentiated, non-gelatinized or weakly gelatinized, encrusted with pale yellow-brown pigment; subcutis hyphae cylindrical, 6–14 μm wide, encrusted with pigment; oleiferous hyphae absent. Clamp connections present.

Habitat: On lateritic soil in tropical lowland forest (dominated by Dipterocarpus obtusifolia , mixed with Tectona grandis ) forest, 425 m elev.

Known distribution: Northwest Thailand.

Notes: As pointed out in the key, I. fragilissima is the third Thai species (cf. I. brevisquamulosa , I. pusillima ) with remarkably small basidiomes. It is recognized, in particular, by the predominantly brown basidiomes, innately fibrillose pileus, pruinose stipe in its upper portion only and the small weakly nodulose or angular basidiospores. The species is placed phylogenetically in sect. Petiginosae ( Fig. 1 ) with strong support.

Figures

FIGURE 1. nLSU ML phylogeny of the Inocybaceae (with outgroups pruned) illustrating the autonomous placement and highly polyphlyetic nature of Thai and Malay species of Inocybe in bold (note that I. petchii and I. gemina are not present in the tree). Numbers above and below branches represent ML bootstrap values.

PLATE 5. a. Inocybe fragilissima (DED8061, holotype). b. Inocybe pileosulcata (DED8058). c. Inocybe parvibulbosa (ZT10099, holotype). d. Inocybe parvibulbosa (DED8021). Scale bars = 10 mm. Photos a, b, d, by Dennis Desjardin, c, by Egon Horak.

PLATE 8. SEM images. a. Basidiospores of Inocybe hydrocybiformis (ZT10077); scale bar = 2 μm. b. Basidiospores of Inocybe stellata (ZT10097, holotype); scale bar = 2 μm. c. Basidiospores of Inocybe thailandica (DED8049, holotype); scale bar = 5 μm. d. Hymenial cystidia of Inocybe angustifolia (ZT10149); scale bar = 10 μm. e. Basidiospores of Inocybe brevisquamulosa (ZT10102, holotype); scale bar = 2 μm. f. Basidiospores of Inocybe pusillima (ZT10130); scale bar = 2 μm. g. Basidiospores of I. fragilissima (DED8061, holotype); scale bar = 2 μm. h. Basidiospores of Inocybe ornata (ZT10107, holotype); scale bar = 3 μm. i. Basidiospores of Inocybe parvibulbosa (ZT10099, holotype). Scale bar = 2 μm. Photos by U. Jauch & M Kirchmair.

FIGURE 14. Macroscopic and anatomical features for Inocybe fragilissima (DED8061, holotype). a. Basidiomes. b. Basidiospores. c. Basidia. d. Cheilocystidia.e. Paracystidia.f. Pleurocystidia.g. Caulocystidia.h. Pileipellis. Scale bars:basidiomes = 20 mm, basidiospores = 10 μm, basidia and cystidia = 20 μm, pileipellis = 40 μm. Drawings by Egon Horak.