Mycena oboensis A.C. Cooper, Desjardin & B.A. Perry, 2018

Cooper, Alexandra C., Desjardin, Dennis E. & Perry, Brian A., 2018, The genus Mycena (Basidiomycota, Agaricales, Mycenaceae) and allied genera from Republic of São Tomé and Príncipe, West Africa, Phytotaxa 383 (1), pp. 1-47 : 31

13. Mycena oboensis A.C. Cooper, Desjardin & B.A. Perry , spec. nov. ( Fig. 23 )

MycoBank no.: MB 825515

Holotype:—AFRICA. São Tomé, Parque Nacional Obo , Lagoa Amelia Trail, N 00˚16.922’, E06˚36.062’, 25 April 2008, D.E. Desjardin and B.A. Perry, BAP 669 ( SFSU).

Etymology:—referring to the site where the holotype was collected, Parque Nacional Obo.

Diagnosis:— Pileus 1.5–3 mm diam, initially paraboloid, becoming plane with a central depression, striate; surface dull, dry, minutely granulose, disc with black pruinae, less pruinose towards the margin, white. Lamellae adnate with a short decurrent tooth, subdistant with 1 series of lamellulae, broad, white. Stipe 8–14 × <0.5 mm, central, terete, cylindrical, arising from a small, pubescent basal disc; surface dull, dry, pubescent, white. Odour and taste not recorded. Bioluminescence undetected.

Basidiospores (6.4–) 7.2–8.8 × (4.0–) 4.8–5.6 μm [x m = 7.92 ± 0.73 × 4.84 ± 0.41 μm, Q = 1.33–1.83, Q m = 1.64 ± 0.12, n = 20, s = 1], ellipsoid, smooth, hyaline, amyloid, thin-walled. Basidia 11.2–16.8 × 7.2–10.4 μm, clavate, hyaline, inamyloid, thin-walled, 2-spored, sterigmata up to 1.5 μm long. Basidioles clavate. Cheilocystidia absent. Pleurocystidia absent. Pileipellis a cutis with acanthocysts and cherocytes; hyphae 2.4–4.0 μm diam, repent, cylindrical, smooth, hyaline, dextrinoid, thin-walled, non-gelatinous. Cherocytes scattered, 21–51 × 18–39 μm, globose to ovoid or pyriform, with knob-like projections over the upper half, apically thick-walled (3–10 (–23) μm), walls hyaline, contents greyish brown; projections 1.5–5 × 1.5–3.2 μm, solid. Acanthocysts common, 15.2–39 × 11.2–24 μm, globose, densely spinulose, thin-walled, hyaline, inamyloid; spinulae 0.8–1.6 × 0.5–0.8 μm. Marginal cystidia common, 16–53 × 10.4– 14.4 μm, clavate to fusiform, densely spinulose on the upper half or apex, thin-walled, hyaline, inamyloid; spinulae 0.8–1.6 × 0.5–0.8 μm. Hypodermium composed of inflated hyphae up to 21 μm diam, hyaline, inamyloid, thin-walled. Hymenophoral trama hyphae 2.4–8.8 μm diam, hyaline, dextrinoid, non-gelatinous, thin-walled. Stipitipellis a cutis; cortical hyphae 2.4–7.2 μm diam, parallel, cylindrical, hyaline, dextrinoid, thin-walled; medullary hyphae 9.6–29 μm diam, smooth, hyaline, dextrinoid, thin-walled. Caulocystidia abundant; 23–79 × 5.6–10.4 μm, cylindrical to fusiform, densely spinulose, hyaline, inamyloid, thin-walled; spinulae 1.6–2.4 × 0.8–1.6 μm. Clamp connections present in all tissues.

Habitat and known distribution:—Gregarious on decaying seed of undetermined dicotyledonous tree in upland forest. ( São Tomé). Only known from the holotype.

Notes:— Mycena oboensis is distinguished by tiny basidiomata with a white, striate pileus with scattered black pruinae, white, adnate lamellae with a decurrent tooth, a white, pubescent stipe arising from a small basal disc, basidiospores with mean 7.9 × 4.8 μm (Q = 1.6), 2-spored basidia, an absence of cheilocystidia and pleurocystidia, pileipellis with acanthocysts, very thick-walled cherocytes with brown contents and knobby projections, distinctive marginal cystidia, and cylindrical caulocystidia covered with spinulae. The macromorphology of M. oboensis is nearly indistinguishable from that of M. lasiopus , but the latter has a more grey pileus, shorter stipe (up to 7 mm), grows on sticks, has longer basidiospores with mean 9 × 4.8 μm (Q = 1.9), spinulose cheilocystidia, irregular-shaped cherocytes with tiny spinulae, lacks distinctive marginal cystidia, and has much longer caulocystidia with apically more sparse spinulae. The European M. rhenana Maas Geest. & Winterh. shows some affinities with M. oboensis (lacks cheilocystidia), but forms a pileus without black pruinae, has narrower basidiospores (3.8–4.3 μm), 4-spored basidia, non-spinulose caulocystidia, and lacks cherocytes ( Maas Geesteranus & Winterhoff 1985).

Pairwise comparisons of aligned, overlapping ITS sequences of the São Tomé specimen (BAP 669) with the top ten BLAST results show 88.2% similarity to four sequences determined as M. corynephora , a European species in sect. Sacchariferae . Interestingly, the ITS sequence of M. oboensis is only 71.2% similar to that of M. lasiopus because of multiple insertions in M. oboensis . In the ITS phylogeny ( Fig. 2), M. oboensis clusters with two additional members of sect. Sacchariferae from ST&P ( M. lasiopus , M. alphitophora ) in a clade with other members of the section (92% BS, 1.0 PP support).

Figures

FIGURE 23. Mycena oboensis (BAP 669, Holotype). a. Basidiospores. b. Basidia. c. Acanthocysts. d. Cherocytes. e. Pileus marginal cystidia. f. Caulocystidia. Scale bar = 10 μm.