Hydropus murinus 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 : 40-42

18. Hydropus murinus A.C. Cooper, Desjardin & B.A. Perry , spec. nov. ( Figs. 32 , 33 )

MycoBank no.: MB 825518

Holotype:—AFRICA. São Tomé, Macambrara radio antenna area, above 1300 meters, N00˚16.557’, E06˚36.326’, 25 April 2008, D.E. Desjardin and B.A. Perry, BAP 657 ( SFSU).

Etymology:— murinus (L.) = mouse grey – referring to the mouse grey colour and mouse hair-like texture of the pileus surface.

Diagnosis:— Pileus 4–11 mm diam, broadly paraboloid to convex when young, becoming plano-convex and centrally depressed to umbilicate in age, margin entire, striatulate; surface dull, dry, minutely pruinose with dark brown granules and very short hairs, disc dark brown (6–7F7–8), fading to light brown, margin greyish brown, fading to greyish white. Lamellae decurrent, close to subdistant with 2 series of lamellulae, off-white, developing brown tones when drying; edge concolorous. Stipe 7–16 × 0.5–1 mm, central, terete, cylindrical, hollow; surface minutely pruinose, with dark brown granules and short brown hairs, greyish white to pale yellowish brown, darkening in age from base upwards. Odour indistinct; taste not recorded. Bioluminescence undetected.

Basidiospores 7.2–8.0 × 4.0–4.8 μm [x m = 7.72 ± 0.39 × 4.44 ± 0.41 μm, Q = 1.50–2.00, Q m = 1.75 ± 0.12, n = 20, s = 1], ellipsoid, smooth, hyaline, amyloid, thin-walled. Basidia 17.6–35 × 5.6–7.2 μm, clavate, hyaline, inamyloid, thinwalled, 4-spored, sterigmata up to 5.6 μm long. Basidioles clavate. Lamellar edge sterile. Cheilocystidia 42–81 × 4.8–

10.4 μm, fusiform to subclavate or cylindrical, occasionally strangulate, hyaline, inamyloid, thin-walled. Pleurocystidia uncommon, narrowly fusiform, similar to cheilocystidia. Pileipellis a cutis with differentiated terminal cells; hyphae

7.2–10.4 μm diam, cylindrical, smooth, hyaline or with brown contents, inamyloid, thin-walled. Terminal cells repent to erect, 23–55 × 8.8–14.4 μm, subclavate to fusoid, with brown contents, inamyloid, thin-walled. Hypodermium absent.

Hymenophoral trama regular to subregular; hyphae 4–18 μm diam, hyaline, inamyloid, non-gelatinous, thin-walled.

Stipitipellis a cutis with caulocystidia; cortical hyphae 3.2–9.6 μm diam, parallel, cylindrical, hyaline, inamyloid, thin-walled; medullary hyphae 5.6–11.2 μm diam, smooth, inamyloid to weakly dextrinoid, thin-walled. Caulocystidia abundant; 26–67 × 5.6–13 μm, fusoid to cylindrical, occasionally geniculate, hyaline or occasionally with brown contents, inamyloid, thin-walled. Clamp connections present in all tissues.

Habitat and known distribution:—Gregarious on decaying wood in secondary upland forest. ( São Tomé). Only known from the holotype.

Notes:— Hydropus murinus is distinguished by convex-umbilicate, pruinose, dark brown to grey pileus 4–11 mm diam, decurrent, off-white lamellae, a hollow, pruinose, greyish white stipe 7–16 × 0.5–1 mm, amyloid basidiospores with mean 7.7 × 4.4 μm, 4-spored basidia, fusiform to cylindrical cheilocystidia and pleurocystidia, a cutis-type pileipellis with numerous subclavate to fusoid, brown terminal cells, fusoid to cylindrical caulocystidia, and lignicolous habit. In combination, these features indicate placement in sect. Hydropus , subsect. Marginelli Singer (1982).

The São Tomé taxon is morphologically closest to H. cavipes (Pat.& Gallard) Dennis and H. atropruinosus (Corner) Singer. Hydropus cavipes , described from Venezuela, forms larger basidiomata with an olive brown, translucently striate pileus 15–70 mm diam, adnate lamellae, a stipe 17–60 × 2–8 mm, smaller basidiospores with mean 6 × 4 μm, and broader hymenial cystidia (up to 18 μm diam) (Singer 1982, Pegler 1983). Hydropus atropruinosus , described from Brazil, forms much smaller basidiospores (5.5–6.3 × 2.7–3 μm, and ventricose to clavate cheilocystidia with a narrow apical prolongation up to 35 μm long ( Corner 1966, Singer 1982). The temperate H. marginellus (Pers.) Singer differs from H. murinus in forming larger pilei (10–30 mm diam), crowded, conspicuously brown-marginate lamellae, clavate to utriform or lageniform cheilocystidia, and lacks conspicuous pleurocystidia ( Kühner 1938, Ludwig 2001, Laessøe 2008).

Pairwise comparisons of aligned, overlapping ITS sequences of H. murinus (BAP 657) with the top ten BLAST results indicate 99.7% similarity to two sequences from Australia determined as Hydropus sp. (KP012822, KP012912). These results suggest that there occurs a species in Australia that is conspecific with our material from São Tomé, and consequently, that the present taxon is widespread. Cooke (1892) and others (cited in May and Wood 1997) reported H. putredinus (Berk. & M.A. Curtis) Pegler (as Marasmius putredinus ) from Australia. Pegler (1987), who studied the holotype specimen of M. putredinus , a species described from Cuba, noted the close similarity of H. putredinus with H. cavipes (noted above as similar to H. murinus ), but indicated that H. putredinus had inamyloid basidiospores. Hydropus putredinus differs from H. murinus in forming larger basidiomata (pilei 12–25 mm diam) with a solid stipe and smaller inamyloid basidiospores (mean 6 × 3.7 μm) (Pegler 1987).

In the ITS phylogeny, H. murinus is sister to H. marginellus plus H. atramentosus with high support (100% BS, 1.0 PP).

Genus, uncertain

Figures

FIGURE 32. Basidiomata of Hydropus murinus (BAP 657, Holotype). Scale bar = 10 mm.

FIGURE 33. Hydropus murinus (BAP 657, Holotype). a. Basidiospores. b. Basidia. c. Cheilocystidia and pleurocystidia. d. Pileipellis terminal cells. e. Caulocystidia. Scale bar = 10 μm.