Agaricus murinocephalus R.L. Zhao, Desjardin & K.D. Hyde 2013
Index Fungorum number 564460, MycoBank: MB564460
Pileus 30 mm diam. when young, then expanding to 50–55 mm diam., convex with distinct broad umbo; margin deflexed, splitting with age, never uplifted; surface dry, covered with fibrils or very finely squamulose; disc generally greyish brown (5F5) to black or sometimes with greenish tones; ornamentation disrupted towards the whitish margin and appearing minutely pulverulent on a whitish background. Context 3 mm thick at disc, white. Lamellae free, crowded, with 4 series of lamellulae, 5–6 mm broad, ventricose, at first white, then light orange grey (6B2), later greyish brown (8D3), finally dull brown to dark brown. Stipe 40–70 × 4–5 (apex) × 5–10 (base) mm, cylindrical to subclavate above a bulbous base, hollow; surface smooth, silky, white. Annulus 2 mm broad, collar-like, broken, ephemeral, white. Odor pleasant. Surfaces of stipe and pileus staining reddish-brown on touching; context lacking color change or very slightly discoloring yellow at the base of stipe on cutting. Basidiospores 5.5–7 × 3–4 µm, [x = 6 ± 0.4 × 3.5 ± 0.3 µm, Q = 1.4–2.0, Qm = 1.75 ± 0.35, n = 20], elongate-ellipsoid, without germ pore, smooth, brown. Basidia 12–19 × 6–8 µm, hyaline, smooth, 4-spored. Cheilocystidia scattered, 9–24 × 8–13 µm, pyriform to broadly clavate, hyaline, smooth. Pleurocystidia absent. Pileipellis a cutis formed from hyphae 5–10 µm diam., some constricted at septa, cylindrical, walls hyaline, containing brown vacuolar pigment. Annulus composed of hyphae of 4–7 µm diam. that are smooth, hyaline and branched. Macrochemical reactions KOH reaction bright yellow; Schäffffer reaction negative. (Figs. 1–2)
Type: Thailand. Chiang Mai Prov., Mae Taeng, Ban Mae Sae village, on Hwy 1095 near 50 km marker, 19°14.599ʹN 98°39.456ʹE, altitude 962 m, 10 June 2006, coll. Todd Osmundson ZRL3044 (Holotype, BBH 19560; isotype SFSU; GenBank, JF691555). Etymology: from murinus = mouse-grey, and cephalus = headed; referring to the greycolored pileus.
Habit: solitary or scattered in small groups in open areas of forest.
Material examined: THAILAND, Chiang Rai Prov., Mae Sai, Doi Tung, 3 August 2006, coll.: Rui-lin Zhao ZRL3092(BBH 19608, SFSU).
Notes: Although some morphological characters of A. murinocephalus, such as the slightly reddish-brown discoloration on bruising of the pileus and the lack of typical phenolic odor are not typical for A. sect. Xanthodermatei, the molecular phylogenetic position (Zhao et al. 2011), negative Schäffer reaction, positive KOH reaction, and pileipellis hyphae with vacuolar pigments support this new species in this section. Furthermore, the previous molecular work separates this new species from A. endoxanthus, A. microvolvatulus Heinem., A. xanthodermulus Callac & Guinb., A. xanthodermus, and A. xanthosarcus Heinem. & Gooss.-Font. Specimen NTF61 (see sp. 39 in the Zhao et al. 2011 phylotree) represents another possible species sister to A. murinocephalus that our molecular analyses show as a different new species. A complete morphological and molecular characterization of specimen NTF61 will bepresented in another paper. The context in A. murinocephalus either does not stain yellow or discolors only slightly on exposure. Most sect. Xanthodermatei species stain distinctly yellow after being cut, especially at the stipe base of the stipe, e.g. A. bulbillosus Heinem. & Gooss.-Font., A. endoxanthus, A. iodosmus Heinem., A. moelleri Wasser, A. menieri Bon, A. pseudopratensis (Bohus) Wasser, A. xanthodermus, A. xanthosarcus (Cappelli 1984, Heinemann 1956a, 1978; Kerrigan 1986, Nauta 2001). In some species, such as A. phaeolepidotus (F.H. Møller) F.H. Møller, A. californicus Peck, or A. hondensis Murrill, a weak yellow or rubescent discoloration occurs on cutting, however all taxa have a phenolic odor and lack a dark greyish pileus (Cappelli 1984, Kerrigan 1986, Nauta 2001) that characterize A. murinocephalus. Agaricus biannulatus, a recently published species (Parra et al. 2011) in this section also lacks a yellow context discoloration and phenolic or iodine-like odor, but differs from A. murinocephalus in a two-layered annulus consisting of two distinct separate limbs. Agaricus volvatulus Heinem. & Gooss.-Font. and A. placomyces Peck are morphologically similar to our new species in that both have blackish pilei and a bulbous stipe. Agaricus volvatulus, however, has a distinct phenolic odor and its pileus is darkly pigmented overall, while A. placomyces has an elastic annulus that may remain attached to the pileus margin even after pileus expansion (Heinemann 1978, 1980; Kerrigan et al. 2005). (From Zhao et al. 2013)
Fig. 1 Agaricus murinocephalus A–C. Holotype BBH 19560; D. BBH 19608.
Fig. 2 Agaricus murinocephalus (Holotype BBH 19560): A. Longitudinal section of basidiocarp; B. Basidiospores, basidia and cheilocystidia; C. Pileipellis hyphae; D. Annulus hyphae. Scale bars: A = 10 mm; B–D = 10 µm.
Zhao RL, Desjardin DE, Callac P, Parra LA, Guinberteau J, Soytong K, ... & Hyde KD 2013– Two species of Agaricus sect. Xanthodermatei from Thailand. Mycotaxon, 122(1), 187-195.
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