Marasmius megistus Singer, Bull. Jard. Bot. État Brux.

Shay, Jackie E., Desjardin, Dennis E., Perry, Brian A., Grace, Chris L. & Newman, Danny S., 2017, Biodiversity and phylogeny of Marasmius (Agaricales, Basidiomycota) from Madagascar, Phytotaxa 292 (2), pp. 101-149 : 137-138

27. Marasmius megistus Singer, Bull. Jard. Bot. État Brux. 34: 356. 1964. ( Fig. 18 , Plate 7 )

Type:— DR CONGO. Binga, 7 May 1928, M. Goossens–Fontana 733 ( BR 11492–46).

Description:— Pileus 6.5–15 mm diam, campanulate; margin deeply sulcate; surface dry, glabrous; disc yellowish grey (4 B 2), sulcae pale violet brown (10 E 4) to reddish grey (10 B 2), ridges and margin buff (4 A 2) to cream (4 A 3). Context thin. Lamellae subfree, distant (14) broad (1–2 mm wide), buff (4 A 2), non-marginate. Stipe 104–115 × 1–2 mm, central, cylindrical, hollow; surface glabrous; brownish grey (10D2) to brownish red (10 E 6). Odor and taste not distinctive.

Basidiospores (26.4–) 29.6–32.8 (–40) × 4.8–7.2 μm [x mr = 30.7–34.2 × 5.8–6.7 μm; x mm = 32.44 ± 2.49 × 6.23 ± 0.66 μm; Q = 2.8–6.8; Q mr = 5.09–5.33; Q mm = 5.21 ± 0.17, n = 2–27, s =2], narrowly ellipsoid to clavate, smooth, hyaline, inamyloid, thin-walled. Basidia not observed. Basidioles 18.4–57 × 5.6–10.4 μm, clavate to fusoid,

hyaline, inamyloid, thin-walled. Cheilocystidia evenly distributed, of Siccus - type broom cells; main body 16–25.6

× 4.8–9.6 μm, clavate or irregular, 2–3-lobed, hyaline, inamyloid, thin-walled; apical setulae 0.8–8 × 0.8–1.6 μm,

cylindrical to conical, sometimes branched, hyaline, inamyloid, thin-walled. Pleurocystidia absent. Pileipellis not mottled, a hymeniform layer of Siccus - type broom cells; main body 16–32 × 6.4–10.4 μm, clavate or irregular, hyaline,

inamyloid, thin-walled; apical setulae 2.4–8 × 0.8–3.2 μm, few per cell, broadly conical to cylindrical or utriform,

seldom branched, hyaline, inamyloid, thin-walled. Pileus trama interwoven; hyphae 1.6–8 μm diam, cylindrical smooth, hyaline, dextrinoid, thick-walled. Lamellar trama regular; hyphae 2–7.2 μm diam, cylindrical to inflated,

smooth, hyaline to pale yellow, dextrinoid, thin-walled. Stipe tissue monomitic; cortical hyphae 1.6–8 μm diam,

parallel, cylindrical, smooth, pale yellow, green brown, dextrinoid, thick-walled; medullary hyphae 1.6–9.6 μm diam,

parallel, cylindrical to inflated, smooth, hyaline, dextrinoid, thin-walled. Caulocystidia absent. Clamp connections present.

Habit, habitat and known distribution:—Solitary on dicotyledonous leaves. Africa ( Burundi, Cameroon, DR

Congo, Tanzania, Uganda), Madagascar.

Material examined:— MADAGASCAR.Region Vatovavy-Fitovinany,District Ifanadiana, Commune Ranomafana,

Ranomafana National Park , Piste B, elev. 1004 m, GPS: 21˚ 15.413’ S, 47˚ 25.253’ E, 22 January 2014, J. E. Shay 163 ( TAN) ; Region Vatovavy-Fitovinany , District Ifanadiana, Commune Ranomafana, February 2013, T. Lockwood 2132155 ( SFSU) .

Notes:— Marasmius megistus forms some of the largest basidiospores in the genus. The Madagascan material is distinguished by a relatively small (up to 15 mm diam) sulcate striped pileus with violet-brown sulcae and cream ridges, distant non-marginate lamellae, a very long (up to 115 mm) glabrous stipe, basidiospores in the range 29.6–40 × 4.8–7.2 μm, no pleurocystidia, Siccus - type broom cells with few setulae, and growth singly on dicotyledonous leaves. Antonín (2007) reports the species as forming a larger pileus (26–50 mm diam) but in all other respects the specimens from Madagascar match those reported from tropical Africa. ITS sequences of two Madagascan specimens ( KX148992 , KX148993 ) are sister to a specimen from São Tomé ( KX953750 ) with strong support (100% BS, 1.0 PP; Fig. 1a ) .

Figures

FIGURE 1a. Maximum likelihood phylogeny based on ITS sequence data. Marasmius from Madagascar are indicated in bold type.Values separated by / refer to nonparametric ML bootstrap proportions and Bayesian posterior probabilities, respectively. Values greater than 70/0.70 are shown (- designates a value below 70% or below 0.70). Nodes receiving support values greater than 90/0.95 are represented by bold branches. G—sect. Globulares; N—sect. Neosessiles; SA—sect. Sicci ser. Atrorubentes; SL—sect. Sicci ser. Leonini; SH—sect. Sicci ser. Haematocephali.

PLATE 7. Basidiocarps representing sect. Sicci ser. Leonini a) Marasmius megistus (JES 163) b) Marasmius megistus (Lockwood 2132155), photo generously donated by Taylor Lockwood, c) Marasmius bambusiniformis (JES 199). Scale bar = 10 mm (a, c); 5 mm (b). Photography by D.S. Newman.

FIGURE 18. Marasmius megistus (JES 163, Lockwood 2132155) a) basidiospores; b) basidioles; c) cheilocystidia; d) pileipellis cells. Scale bar = 10 μm. Illustrated by J.E. Shay.