Agaricus desjardinii Z.R. Wang, K.D. Hyde & R.L. Zhao, 2015

Wang, Zhuo-Ren, Callac, Philippe, Zhou, Jun-Liang, Fu, Wen-Jin, Dui, San-Han & Zhao, Rui-Lin, 2015, Edible species of Agaricus (Agaricaceae) from Xinjiang Province (Western China), Phytotaxa 202 (3), pp. 185-197 : 188-191

Agaricus desjardinii Z.R. Wang, K.D. Hyde & R.L. Zhao , spec. nov. (Figure 2: A–C; Figure 3)

MycoBank: MB 810517

Typus:— CHINA, Xinjiang Province, Bortala, Ebinur Lake, 10 May 2012, WZR2012 8212, collected by Zhuo-Ren Wang, (holotypus HMAS!, isotypus SWFC!).

Pileus 30–50(–80) mm in diameter, usually pulvinate (cushion-like) or parabolic when young, plane to slightly depressed at the center with inrolled margin; surface covered by thick, large, triangular scales, erect or recurved, white, light brown, and quickly discolouring, reddish-brown, brown, or dark brown on bruising or dehydration. Lamellae free, crowded, narrow, up to 5 mm wide, edge entire, concolorous with lamellae sides. Lamellulae in several series. Stipe 40–60 × 20–30 mm, cylindrical, or ventricose fusiform, straight or curved, with tapering base, stuffed; surface below the annulus covered by scales which are similar to those of pileus, recurved, white, but soon becoming reddish-brown to brown on touching, surface above the annulus glabrous, white. Annulus intermediate, persistent, single, thick and narrow (band-like), fibrillose, up to 4 mm broad, smooth at the upper side and floccose at the lower side. Context firm, white to light greyish-white, discolouring reddish-brown, especially in the pileus and the stipe base. Odour mushroomy.

Macrochemical reactions: KOH negative; Schäffer reaction negative.

Basidiospores 6.2–8 × 4.9–6.8 μm, avX = 7 ± 0.5 × 5.7 ± 0.6 μm, Q = 1.1–1.4, avQ = 1.23, n = 25, subsphaerical to broadly ellipsoid, smooth, thick-walled, brown, without apical pore. Basidia 30–40 × 4–7 μm, clavate or narrowed and cylindrical towards the base, hyaline, 2 or 4-spored, with sterigmata 2–4 μm long. Cheilocystidia and pleurocystidia absent. Pileipellis a cutis composed of cells 43–52 × 7–10 μm, cylindrical, branched, smooth, slightly constricted at the septa, with yellowish-brown parietal pigment. Annulus composed of cells 40–50 × 8–12 μm, hyaline, smooth, constricted at septa, distinctly inflated near the ends.

Diagnosis:—This species can be distinguished within section Nigrobrunnescentes by its large recurved scales on the pileus, larger spores, quick and strong reddish-brown or brown discolouration on bruising and absence of cheilocystidia.

Habit, habitat and distribution:—gregarious, often in groups of two basidiomata in reedy grassland. Only known from China.

Etymology:—the epithet “desjardinii ” honors the mycologist Dennis E. Desjardin who is one of authors of the section Nigrobrunnescentes .

Other materials examined:— CHINA, Xinjiang Province, Bortala, Ebinur Lake , 10 May 2012, WZR2012 907 collected by Zhuo-Ren Wang ( SWFC!; HMAS!) .

Notes:—The most similar species to A. desjardinii both morphologically and phylogenetically is A. boisseletii Heinem. Both have stout basidiomata and distinctly large scales on the pileus. However, under the microscope, A. boisseletii has smaller and wider spores (5–6.8 × 4–4.5 μm, avQ =1.44), and usually catenulate cheilocystidia ( Parra 2008). Agaricus nigrobrunnescens , the type species of this section, and the new species both have large scales on the pileus, however A. nigrobrunnescens has much smaller spores (4.2–5.8 × 3.3–4.5 μm) and abundant cheilocystidia ( Peterson et al. 2000). Agaricus fuscovelatus , described from North America, is also similar to the new species by its stout and deeply rooting stipe as well as its spore size and shape, but A. fuscovelatus has appressed squames on the pileus and presents cheilocystidia ( Kerrigan 1986). Agaricus padanus (see below), a species also having abundant velar remnants below the annulus can be easily distinguished by its much less reddening context and its abundant clavate cheilocystidia. This new species also differs from European species belonging to section Sanguinolenti , which is close to section Nigrobrunnescentes , such as A. benesii Pilát , by having pilei covered by fibrils or tiny fibrillose squames ( Nauta 2001; Parra 2008), which are quite different from the large scales of this new species, or Agaricus sylvaticus Schaeff. a species having much smaller spores (4.5–6.5 × 3.2–4.2 μm) and abundant cheilocystidia; There are some similar species assigned to A. sect. Sanguinolenti reported from South America and tropical Asia, such as A. dicystis Heinem. and A. pleurocystidiatus Heinem. , however, those species are slender and have smaller spores (Heinemann 1978,1980,1986,1990).