Agariucs brunneogracilis R.L. Zhao & K.D. Hyde, 2016

Zhou, Jun-Liang, Su, Sheng-Yu, Su, Hong-Yan, Wang, Bo, Callac, Philippe, Guinberteau, Jacques & Zhao, Rui-Lin, 2016, A description of eleven new species of Agaricus sections Xanthodermatei and Hondenses collected from Tibet and the surrounding areas, Phytotaxa 257 (2), pp. 99-121 : 110-118

Section Xanthodermatei

1 Agariucs brunneogracilis R.L. Zhao & K.D. Hyde , sp. nov. ( Fig. 3 : A–E)

MycoBank NO.: MB 812310

Diagnosis: this species is characterized by slender basidiomata, a cap completely covered with grayish brown scales, a long clavate and smooth stipe, a movable annulus, a lack of phenolic or iodine-like odor, and elongated ellipsoid basidiospores (5.9–6.9 × 3.2–3.8 μm).

Etymology: the word “brunneogracilis ” refers to the brown pileus and slender habit; from ‘brunneus’ (Latin) brown, and ‘gracilis’ (Latin) slender.

Material examined: Thailand, Chiang Mai Prov., Mae Taeng Dist., Ban Pha Deng Village , N 19°17′04″, E 98°44′47″, elevation 900 m, 30 June , 2008, Rui-Lin Zhao ( ZRL258 MFLU HOLOTYPE; HMAS 275738 , ISOTYPE) .

Pileus 22 mm in diam., plane; surface covered with fibrillose squamules, entirely grayish brown (5E3); edge straight. Context 1.5 mm thick at the disc, white, and fleshy. Lamellae free and crowded; 5 series of plural-lamellulae, 2 mm broad, pink to brownish orange (6C3) or brown; edge entire. Stipe 1.5 (apex)– 2 mm (above the base)– 5 mm (base) × 60 mm (length); elongated clavate, with rhizomorphs at the base; surface white, smooth and silky; hollow. Annulus single but thick (1 mm thick), movable, 1 mm broad; upper side white and smooth, lower side white, floccose and subperonate. Odor not iodine-like, but pleasant. No color change on touching the stipe, slightly yellow at the base of the stipe on cutting.

Macrochemical reactions: KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 3-D ) 5.9–6.9 × 3.2–3.8 μm [x = 6.4 ± 0.3 × 3.4 ± 0.2 μm, Q = 1.7–2.1, Qm = 1.9 ± 0.1, n = 20 basidiospores], elongated ellipsoid, occasionally cylindrical, smooth, thick-walled, light brown when young and brown when mature. Basidia 13.6–15.4 × 6–7 μm, hyaline, smooth, clavate, and 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 3-E ) a cutis composed of hyphae 4–8 μm wide, long clavate, cylindrical, smooth, containing light brown to brown vacuolar pigments.

Habitat solitary in forests.

Notes: This species is phylogenetically close to A. murinocephalus , but A. murinocephalus has a pileus covered in greyish brown (5F5) to black scales, which are only present at the disc, and a distinctly visible white background and a truncate umbo ( Zhao et al. 2012). Agaricus microvolvatulus is another similar species, but it has smaller and rounder basidiospores (4.2–4.8 × 2.8–3 μm, Heinemann 1978; 4.5–6 × 2.9–3.8μm, Q=1.62–1.67, Thongklang 2014) and a volva-like or abrupt bulbous stipe base ( Heinemann 1978, Thongklang 2014).

2 Agaricus daliensis H.Y. Su & R.L. Zhao , sp. nov. ( Fig. 3 : F–K)

MycoBank NO.: MB 812311

Diagnosis: this species is characterized by large basidiomata, dot-like brown to smoky black scales on the white background of the cap, a stipe surface that changes to reddish brown when touched and small ellipsoid to elongate basidiospores (4.3–5.1 × 2.7–3.2 μm).

Etymology: the word “daliensis ” refers to the place where the holotype was collected.

Material examined: China, Yunnan Prov., Dali , 17 July 2011, Hong-Yan Su ( SHY2011071706 , HMAS 275739 ) ; 31 July 2011, Hong-Yan Su ( SHY2011073114 , HMAS 254643 , HOLOTYPE) .

Pileus 85–120 mm in diam., convex, plano-convex, some subunbonate; margin slightly flared and irregularly grooved; scales small, dot-like, dense at disc, distantly spaced at the margin, arranged concentrically to some degree, brown (oac640) to smoky black (oac902) against a white background; edge decurved to incurved, exceeding into white lace-like around cap. Context white and fleshy. Lamellae free and crowded; with 5–7 series of plural-lamellulae, pink to brown; edge entire. Stipe 15 mm (apex)– 25 mm (base) × 200 mm (length); cylindrical or slightly long clavate; surface white, dry and smooth; hollow. Annulus double, membranous, pendant, more than 40 mm in diam., superior; upper layer white and smooth; lower layer white, slightly flocculent or attached light brown granulose. Odor unknown. Changing to reddish brown upon touching the stipe surface; changing to yellow at the base of stipe upon cutting.

Macrochemical reactions: KOH reaction unknown. Schäffer’s reaction negative.

Basidiospores ( Fig. 3-G ) 4.3–5.1(–5.7) × 2.7–3.2 μm [x = 4.8 ± 0.4 × 2.9 ± 0.1 μm, Q = 1.5–1.9, Qm = 1.7 ± 0.2, n = 20 basidiospores], ellipsoid to elongate, smooth, thick-walled, brown. Basidia 13.2–16.1 × 3.9–5.6 μm, hyaline, smooth, clavate, and 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 3-F ) a cutis composed of hyphae 4.5–12.9 μm in diam. and has cylindrical cells that are often broadly clavate, ellipsoid and constricted at the septa near apex, smooth, containing light brown to brown vacuolar pigments.

Habitat solitary or scattered.

Notes: The features of the pileus and basidiospores of this species are quite similar to those of A. moelleri [= A. praeclaresquamosus A.E. Freeman (1979: 90) = A. meleagris (Jul. Schäff.) Pilát (1951: 106) ] collected from Northern America and Europe ( Cappelli 1984; Kerrigan 1986; Freeman 1979). However, this new species differs in its cylindrical to slightly clavate stipe and in its lack of cheilocystidia. Agaricus daliensis is similar to A. iodosmus Heinem. (1965: 399) [= A. xanthodermus var. pilatianus Bohus (1971: 80) ] in that it has dark grey squamules on its pileus and a cylindrical stipe; however, the latter known species has larger basidiospores (5.5–7 × 4.5–5.5 μm) ( Heinemann 1990). Molecular data also demonstrates that these are distinct species.

3 Agaricus gregariomyces J.L. Zhou & R.L. Zhao , sp. nov. ( Fig. 4 : F–K)

MycoBank NO.: MB 812314

Diagnosis: this species can be recognized by its medium to large basidiomata, a cap completely covered by grayish brown fibrillose squamules, a bulbous stipe base, a reddish yellow tone on touching and cutting, and elongated basidiospores (5.62–6.3 × 3.52–4.0 μm).

Etymology: the word “gregariomyces ” refers to the gregarious habit; from ‘gregarius’ (Latin).

Material examined: China, Tibet, Milin County, Pai Town, Gongbujiangda Natural Reserve, N 29°46′18″, E 94°43′51″, elevation 3351.10 m, 31 July 2012, Sheng-Yu Su (ZRL2012624, HMAS 254645, HOLOTYPE).

Pileus 50–100 mm in diam., campanulate or conic when young, then convex with umbo, plano-convex or plane when mature; surface dry, covered with grayish brown (8E2) fibrils, radially ranked, breaking up into fibrillose scales towards the margin, with some recurved; edge decurved. Context 3–7 mm thick at the disc, white and fleshy. Lamellae free and crowded; with 8 series of plural-lamellulae, 6–9 mm broad, reddish-brown to dark brown; edge entire. Stipe 5–12 mm (apex)– 18–20 mm (base) × 50–90 mm (length); cylindrical with a bulbous base; surface white and smooth; hollow. Annulus complex, 6–11 mm wide; first composed of 2 membranous layers and filled with heavy fibrillose hair between them, then shrinking into one membranous layer with a thickened edge; upper and lower sides smooth, white, sometimes with yellow tone. Odor not iodine-like, but pleasant. Changing to yellow and then reddish yellow, finally becoming blackish brown after bruising the stipe; slightly reddish yellow on cutting at the disc and base of the stipe.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 3-F ) 5.6–6.3(–6.7) × (3.1–) 3.5–4.0(–4.3) μm [x = 6.1 ± 0.2 × 3.7 ± 0.1 μm, Q = 1.6–1.9, Qm = 1.7 ± 0.1, n = 20 basidiospores], elongate, smooth, thick-walled, light brown when young and dark brown when mature. Basidia 20.0–22.5 × 5.8–7.1 μm, hyaline, smooth, clavate and 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 3-H ) a cutis composed of hyphae 3.9–7.1 μm in diam., long cylindrical, smooth, constricted at the septa, and containing brown pigments.

Habitat gregarious on grassland.

Notes: Agaricus gregariomyces is phylogenetically distant from most known species from section Xanthodermatei , and its closest relative is A. pseudopratensis from Europe, which also has a reddish tone on cutting. However, A. pseudopratensis has cheilocystidia and less elongated basidiospores (Q=1.42–1.65); macromorphologically its squamules are only concentrated at the disc.

4 Agaricus karstomyces R.L. Zhao , sp. nov. ( Fig. 5 : A–G)

MycoBank NO.: MB 812315

Diagnosis: this species can be recognized by its medium to large basidiomata, a pileus covered with dark brown to dark brown grey dot-like squamules, a lack of phenolic or iodine-like odor and elongated basidiospores (5–6.5 × 3–3.5 μm).

Etymology: the word “karstomyces ” refers to its environment which has a large amount of limestone; from ‘karst’.

Material examined: China, Yunnan Prov., Shizong County, Yingwu Mountain Forest Park, N 24°38′24″, E 104°08′49″, elevation 2350.83 m, 29 June 2011, Jie Chen (ZRL2011048, HMAS 254644, HOLOTYPE).

Pileus 90–120 mm in diam., plano-convex, plane, deeply split; covered with squamules, appressed, dot-like, dense at the disc and becoming more sparse towards the margin; dark brown to dark brown grey (oac647) and lighter towards the edge; edge straight. Context 6 mm thick at the disc, white with a grey tone at the centre of the pileus, fleshy. Lamellae free and crowded; more than 6 series of plural-lamellulae, 8 mm in broad, ventricose, pink when young, brown to dark brown when mature, edge entire. Stipe 8–13 mm (apex) – 13–15 mm (base) × 120–140 mm (length); cylindrical to long clavate; surface dry and smooth or slightly fibrillose, white; hollow. Annulus single, membranous, 8 mm in diam.; pendant, large, white; lower side floccose. Odor pleasant. Not discoloring on touching, although the stipe turns slightly yellow on cutting.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 5-D ) 5–6.5 (–7) × 3–3.5 (–4) μm [x = 5.9 ± 0.5 × 3.3 ± 0.3 μm, Q = (1.4–)1.7–2.3, Qm = 2 ± 0.3, n =20 basidiospores], elongate to cylindric, smooth, brown, thick-walled. Basidia 13–17 × 5–6 μm, hyaline, smooth, 4-spored. Cheilocystidia ( Fig. 5 E–G ) clavate, pyriform to subspherial, 11–18 × 6–9 μm, with 2 elements (14–16 μm in diam.) occasionally observed in chain. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 5–7 μm wide and up to 14 μm in diam.; terminal cells long-clavate to clavate, smooth, slightly constricted at septa, containing brown vacuolar pigment. Annulus composed of a cylindrical cell, slightly constricted at the septa, 4–5 μm wide, hyaline.

Habitat scattered in grassland.

Notes: This species was collected from Karst mountain, Yingwushan in the Yunnan Province and is close to A. deardorffensis nom. prov. (from America) in terms of its phylogeny (Kerrigan 2015). Agaricus karstomyces differs from A. deardorffensis by the following: 1) on cutting, the latter has a strong yellow discoloration at the base of stipe, while A. karstomyces becomes slightly yellow at the middle of the stipe, and 2) A. deardorffensis has narrower basidiospores (Q = 1.39) and cheilocystidia, which are similar to the basidia in shape and size.

Agaricus karstomyces is similar to A. sinoplacomyces in its medium to large basidiomata, large annulus, cap characteristics and spore size and shape. Agaricus karstomyces , however, differs in its equal clavate stipe, lack of or faint yellow discoloration on cutting, and cheilocystidia.

This new species is quite similar to A. placomyces in the field; however, A. placomyces has more robust basidiomata and wider basidiospores ( Heinemann 1986; Freeman 1979).

5 Agaricus malangelus Kerrigan nom. prov. ( Fig. 5 : H–J)

Material examined: China, Tibet, Linzhi county, Cypress King garden, N 29°37′21″, E 94°24′07″, elevation 3059.32 m, 31 July 2012, Guang-Ping Li (ZRL 2012628, HMAS).

Pileus 40 mm in diam., rectangular, plane; covered in large scales, recurved, mostly black brown to black (oac625), cracked and revealed white flesh; edge decurved. Context 10 mm-thick at the disc, white and fleshy. Lamellae free and crowded; 7 mm broad, light pink to brown; edge entire. Stipe 13 mm (apex)– 22 mm (base) × 95 mm (length); cylindrical with sub-bulbous base; surface white, dry and smooth; hollow. Annulus single, thick on the edge (up to 4 mm in thickness), pendant, 12 mm in diam.; upper side white and smooth, lower side slightly brown and flocculent. Odor indistinct. Changes to reddish brown on touching at the surface of the stipe and slightly yellow at the base of stipe on cutting.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 5-J ) 4.9–6.8 × 3.9–4.9 μm [x = 4.8 ± 0.3 × 3.7± 0.3 μm, Q = 1.2–1.5, Qm = 1.3 ± 0.1, n = 20 basidiospores], broadly ellipsoid to ellipsoid, smooth, thick-walled, brown. Basidia 16.9–18.1 × 4.4–6.8 μm, hyaline, smooth, clavate, 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 3.1–6.2 μm wide, long clavate, smooth and not constricted at the septa, walls hyaline, containing light-brown vacuolar pigment.

Habitat solitary under Cypress trees.

Notes: This Chinese specimen morphologically matches A. malangelus ( Kerrigan 2016) . There are only two base pair differences in the ITS sequences between this type and the Chinese specimens. Molecular data shows that this species is close to A. menieri , A. moelleri , A. xanthodermus and A. placomyces . The colored pileus clearly differentiates this species from A. xanthodermus , while A. malangelus has broadly ellipsoid to ellipsoid basidiospores. These are quite different from the basidiospores of A. menieri , A. moelleri , and A. placomyces , which are typically ellipsoid to elongated ellipsoid ( Parra 2003; Cappelli 1984; Kerrigan 1986; Nauta 2001; Freeman 1979). Agaricus iodosmus Heinem.(1965: 399) also has a dark cap; however, it has larger basidiospores (6–7 × 4.8–5.1 μm) than those of A. malangelus , and cheilocystidia are present ( Heinemann 1978).

6 Agaricus melanocapus R.L. Zhao sp. nov. ( Fig. 6 : A–F)

MycoBank NO.: MB 812316

Diagnosis: this species can be recognized by its small basidiomata, a pileus covered with dark brown to nearly black minutely fibrillose squamules, a double annulus and small ellipsoid to elongate basidiospores (3.7–4.9 × 2.6–3.2 μm).

Etymology: the word “melanocapus ” refers to the black brown pileus, from ‘melano’ (Latin) black and ‘caput’ (Latin) head.

Material examined: China, Yunnan Prov., Shizong County, Yingwu Mountain Forest Park, N 24°38′24″, E 104°08′49″, elevation 2350.83 m, 28 June 2011, Rui-Lin Zhao (ZRL2011037, HMAS 275734, HOLOTYPE).

Pileus 40 mm in diam., parabolic when young and becoming convex when mature, slightly subumbonate; surface dry with fine fibrillose squamules that are generally dot-like, dark brown (oac 637) to nearly black (oac 626), dense at the disc and covering the whole cap; edge straight. Context 5 mm thick at disc, white and fleshy. Lamellae free and crowded; with 5 series of plural-lamellulae, 5 mm broad, slightly ventricose, pink when young and brown when mature; edge entire. Stipe 6 mm (apex)– 10–12 mm (base) × 90 mm (length); cylindrical to subclavate, with a bulbous base; surface white, smooth and silky; hollow. Annulus double-layered; with a white, upper layer membranous and white; up to 15 mm wide, lower layer fragile, easily torn, some remnants remain attached at the edge of the pileus, crenate, some remain on the lower side of the upper layer, (floccose) and some remain near the stipe bracelet-like (white). Odor indistinct, not iodine-like. Pileus bruising slightly rubescent, and stipe base turns yellow where cut.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 6-E ) 3.7–4.9(5.6) × 2.6–3.2 μm [x = 4.6 ± 0.4 × 2.9 ± 0.2 μm, Q = 1.4–1.8, Qm = 1.6 ± 0.2, n =20 basidiospores], ellipsoid to elongated, smooth, translucent, thick-walled, light brown when young and brown when mature. Basidia 12.5–15.0 × 3.7–5.0 μm, hyaline, smooth, clavate, 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 6-F ) a cutis composed of hyphae 4–18 μm wide; ellipsoid to long clavate, smooth, and always constricted at septa; walls hyaline, containing brown vacuolar pigment. Annulus composed of long cylindrical hyphae, 4–10 μm in diam., with no constriction at the septa, smooth, mostly light yellowish brown and some hyaline.

Habitat: solitary under Rhododendron trees.

Notes: Agaricus melanocapus is morphologically similar to A. endoxanthus . However, the stipe of A. melanocapus has a distinctly bulbous base and lacks cheilocystidia. The ITS sequence data analysis has shown it to be a distinct species from A. endothanthus . This species is phylogenetically close to A. cf. volvatulus (specimen F2767). Agaricus volvatulus ( Heinemann & Goossens-Fontana 1956, Heinemann 1980, Chen et al. 2016) is characterized by a volva-like stipe at its base and abundant cheilocystidia, and thus can be differentiated from A. melanocapus . We also compared this new species with the recently published A. atrodiscus L.J. Chen, Callac, R.L. Zhao & K.D. Hyde , ( Ariyawansa et al. 2015) from section Xanthodermatei in morphology, and our new species differs from this known species by larger sized basidiospores and bulbous base of stipe.”

7 Agaricus tytthocarpus R.L. Zhao , sp. nov. ( Fig. 7 : A–C)

MycoBank NO.: MB 812320

Diagnosis: this species can be recognized by its small basidiomata, the presence of a pileus covered with grayish brown fibrils, a slender and hollow stipe, an annulus with a serrated edge, and elongated basidiospores (5.5–6.4 × 3.2–3.8 μm).

Etymology: the word “tytthocarpus ” refers to the small pileus;from ‘tyttho’ (Latin) small, and ‘caput’ (Latin) head.

Material examined: China, Fujian Prov., Wuyishan City, Longjing Mountain, N 27°38′11″, E 117°56′47″, elevation 324.59 m, 4 Sep. 2011, Xiang-Hua Wang (ZRLWXH3077, HMAS 275741, HOLOTYPE).

Pileus 15–20 mm in diam., conical to convex; surface covered with densely fibrillose, grayish brown (oac868) at the disc, then breaks into small brown scales (not triangle-shaped) towards the margin, white fibrillose near margin; edge straight and sterile overhang, crenate. Context thin, white and fleshy. Lamellae free and crowded; with 5 series of plural-lamellulae, 4 mm broad and brown; edge entire. Stipe 1 mm (apex)– 1.5 mm (base) × 30–40 mm (length); cylindrical, curved, with a smooth white surface; hollow. Annulus membranous, white, subperonate, 2 mm broad; upper side smooth, lower side thick fibrillose; edge serrate. Odor unknown. No color change after touching the stipe. Macrochemical reactions KOH reaction unknown. Schäffer’s reaction negative.

Basidiospores ( Fig. 7-B ) (4.7)5.5–6.4(7.0) × 3.2–3.8 μm [x = 5.9 ± 0.2 x 3.4 ± 0.2 μm, Q = 1.6–1.9, Qm = 1.7 ± 0.1, n = 20 basidiospores], elongated, smooth, thick-walled, brown to dark brown. Basidia 14.6–16.9 × 4.5–5.8 μm, hyaline, smooth, clavate, and 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 7-C ) a cutis composed of hyphae of 2.6–7.1 μm in diam., long clavate, smooth, with no constrictions at the septa; walls hyaline, containing brown vascular pigment.

Habitat scattered in broadleaved forest.

Notes: This is a small and slender agaric, and its cap is heavily fibrillose, which is quite rare in this group. Those characteristics also distinguish it from A. murinocephalus , which is the closest species in terms of phylogeny.

8 Agaricus sinoplacomyces P. Callac & R.L. Zhao , sp. nov. ( Fig. 7 : D–G)

MycoBank NO.: MB 812321

Diagnosis: this species can be recognized by its medium to large basidiomata, a pileus surface covered with pulverulent or fibrillose squamules, a lower annulus surface of annulus with very heavy flocculence, and elongated basidiospores (4.9–5.8 × 2.9–3.3 μm).

Etymology: the word sinoplacomyces refers to the species is recorded from China and similar to A. placomyces ; from ‘sina’ (Latin) China.

Material examined: China, Yunnan Prov., Kunming City, Yeya Lake , N 25°07′15″, E 102°51′47″, elevation 2078.94 m, 30 June 2012, Rui-Lin Zhao ( ZRL2012008 , HMAS 275724 , HOLOTYPE, and ZRL2012009 , HMAS 280514 ) ; Yunnan Prov., Nanjian county, Wuliang Mountain National Natural Reserve , N 24°49′38″, E 100°26′26″, elevation 2634.48 m, 3 July 2012, Philippe Callac ( ZRL2012027 , HMAS 275727 ) and Olivier Raspé ( ZRL2012028 , HMAS 280512 ) ; Sichuan Prov., Chengdu City, Longquanyi district , N 30°33′32″, E 104°16′20″, elevation 523.78 m, 7 October 2011, Bo Wang ( ZRLAG2101 , HMAS 254646 ) .

Pileus 40–100 mm in diam., conical and often truncated when young, then convex and plano-convex to plane when mature, umbonate indistinct or flat, sometimes with a depressed centre; surface covered with fibrillose squamules that break into small squamules towards margin, often pulverulent and sometimes become irregular or mud-cracked after exposure to sunlight, with a dark brown(oac 637) to almost black (oac 626) at the centre, and becomes lighter towards edge, against a white to slightly light brownish-white background that has a red tone upon wetting; margin straight when fresh and decurved after aging and drying. Context 5–8 mm thick at the disc, white and fleshy. Lamellae free and crowded; with 7 series of plural-lamellulae, 4–6 mm broad, pink to pinkish brown when young, and changing into dark brown when old; edge entire. Stipe 7–10 mm (apex)– 14–20 mm (base) × 42–150 mm (length); cylindrical with an abruptly bulbous base; surface white, smooth and silky; hollow. Annulus large, 15–30 mm in diam., membranous and pendant; upper surface white and smooth, lower surface slightly yellowish brown white (oac900) with very heavy flocculence; often extending 1–2 mm in a downward direction and becoming collar-like, surrounding the stipe loosely. Odor not iodine-like, but pleasant. Staining yellow on touching the stipe and distinctly yellow at the base of stipe on cutting.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 7-F ) (4.4)4.9–5.8(6.2) × (2.6)2.9–3.3(4.0) μm [x = 5.3 ± 0.3 × 3.1 ± 0.1 μm, Q = 1.3–1.9 (2.2), Qm = 1.68 ± 0.1, n = 100 basidiospores], most basidiospores elongated, few ellipsoid or cylindrical; smooth, thick-walled, and brown. Basidia 11.5–15.2 × 3.8–6.2 μm, hyaline, smooth, clavate, 4-spored. Cheilocystidia not observed. Pleurocystidia absent. Pileipellis ( Fig. 7-G ) a cutis comprised of hyphae 3.9–9.6 μm wide, broadly clavated and smooth, containing light brown to brown vacuolar pigments, not constricted at the septa. Annulus hyphae 4–8.8 μm in diam., cylindrical to long clavated, hyaline, smooth, and not constricted at the septa.

Habit solitary or scattered in the open areas under trees, both Rhododendron and Fagaceae trees.

Notes: This species is similar to A. placomyces , which is mostly distributed in northern and southern America ( Heinemann 1978, 1986; Freemen 1979). In the field, both have dark grey dot-like squamules on the pileus, stipes with bulbous bases, and a complex annulus. However, under the microscope, the basidiospores of this new species are found to be ellipsoid to elongated (Q = 1.4–1.9), while those of A. placomyces are broadly ellipsoid to ovoid (Q = 1.3–1.4) (from the type specimen by Freeman, 1979). Phylogenetic data also suggest that this new species is distinct from A. placomyces , as there are 5 base pair differences in its sequences data. Agaricus californicus Peck (1895: 203) has dark grey dot-like squamules on the pileus, and it is often present in deciduous forests ( Kerrigan 1986); however, its phenol smell and cylindrical stipe can be used to differentiate it from A. sinoplacomyces .

9 Agaricus tibetensis J.L. Zhou & R.L. Zhao , sp. nov. ( Fig. 7 : H–K)

MycoBank NO.: MB 812322

Diagnosis: this species can be recognized by its small to medium basidiomata, a pileus covered with grey to dark brown squamules, often shell-like at the disc, a slender stipe with a distinct and bulbous base, and ellipsoid basidiospores (6–7 × 4–5 μm).

Etymology: the word “tibetensis ” refers to the Tibet Autonomous Region of China, where the holotype was originally collected.

Material examined: China, Tibet, Milin County, Nanyigou Forest Park , N 29°07′45″, E 94°13′10″, elevation 3003.51 m, 29 July 2012, Sheng-Yu Su ( ZRL2012585 , HMAS 275725 , HOLOTYPE) ; same location, 28 July 2012, Guang-Ping Li ( ZRL2012580 , HMAS 280513 ) ; Tibet, Milin County, Pai town, Gongbujiangda Nature Reserve , N 29°46′18″, E 94°43′51″, elevation 3351.10 m, Rui-Lin Zhao ( ZRL2012617 , HMAS 275731 ) .

Pileus 25–55 mm in diam., parabolic when young, becoming convex, plano-convex or plane when mature; covered with grey (oac902) to dark brown (oac733) appressed or slightly recurved squamules, which are dense and often shell-like at the disc, dark brown to blackish brown (oac733, oac639, oac640), gradually distantly spaced towards margin, sometimes cracked and revealing white flesh; margin decurved, inrolled. Context 2 mm thick at the disc, white and fleshy. Lamellae free and crowded; with 5 series of plural-lamellulae, 4 mm broad, pink, taupe brown (oac753) to brown (oac648); edge entire. Stipe 5–6 mm (apex)– 10–15 mm (base) × 80–120 mm (length); cylindrical with a distinct and bulbous base; surface white, dry and smooth; hollow. Annulus single and thick, rigid, pendant or subperonate, superior, 5–10 mm in diam., upper side smooth and white, lower side white to light grey in color and smooth or slightly floccose. Odor not iodine-like, but pleasant. Discoloring yellow, then reddish brown on the stipe when touched, and bright yellow at the base of the stipe on cutting.

Macrochemical reactions KOH reaction yellow. Schäffer’s reaction negative.

Basidiospores ( Fig. 7-H ) 6–7 × 4–5 μm [x = 6.8 ± 0.2 × 4.2 ± 0.2 μm, Q = 1.4–1.75, Qm = 1.6 ± 0.2, n =60 basidiospores], ellipsoid, smooth, thick-walled, and brown. Basidia 17–24 × 7–8 μm, hyaline, smooth, clavate, 4- spored. Cheilocystidia absent or basidia-like. Pleurocystidia absent. Pileipellis ( Fig. 7-I ) a cutis composed of hyphae 5–10 μm wide, long clavate, smooth, constricted at the septa, with hyaline walls, containing a brown vacuolar pigment. Annulus composed of hyphae similar to those of pileipellis, except lacking pigments.

Habit Solitary or in groups in coniferous forests of Picea asperata , Pinus densata and Platycladus orientalis .

Notes: This new species can be distinguished from other species in this section by its small to medium sized basidiomata, pileus covered in small dark brown squamules, thick annulus, and the distinct bulbous base of its stipe. It has a strong yellow discoloration on cutting. All four samples from Tibet were collected from an elevation above 3000 m. This new species is similar to A. placomyces , as they both grow associated with coniferous forests; however, A. tibetensis has relatively smaller and slender basidiomata and longer basidiospores than those of A. placomyces (more robust basidiomata, with basidiospores less than 6 μm in length) ( Heinemann 1986; Freeman 1979). Agaricus tibetensis is also morphologically similar to A. sinoplacomyces ; however, A. sinoplacomyces was collected from the broadleaf forests and has medium to large basidiomata, smaller basidiospores, and a large and very thin membranous annulus that differs from those of A. tibetensis . The molecular analysis suggests that these two are distinct species.

We also compared this new species with A. deardorffensis from America ( Kerrigan 2016). Although there is only one ITS base pair different between the two, A. deardorffensis is a species with an equal stipe, smaller basidiospores and a strong phenol smell, which are distinctive characters.

Figures

FIGURE 3. A–E. Morphology of A. brunneogracilis (ZRL258 HOLOTYPE):A–C. Basidiomata; D. Basidiospores; E. Pileipellis hyphae. F–K. Morphology of A. daliensis (F–J. SHY2011073114, HOLOTYPE; K SHY2011071706): F. Pileipellis hyphae; G. Basidiospores. H–K. Basidiomata. Scale bar A–C, H–K = 10mm; D–G = 10 μm.

FIGURE 4. A–E. Morphology A.grandiomyces (ZRL2012611, HOLOTYPE):A–C.Basidiomata;D. Basidiospores; E. Pileipellis hyphae. F–K. Morphology of A. gregariomyces (ZRL2012624, HOLOTYPE):F. Basidiospores; G,I–K. Basidiomata, J shows the yellowing staining on the pileus, K shows annulus characters; H. Pileipellis hyphae. Scale bar A–C,G, I–K = 10 mm; D–F = 10 μm; H = 5 μm.

FIGURE 5.A–G.Morphology of A.karstomyces(ZRL2011048, HOLOTYPE):A–C.Basidiomata;D.Basidiospores;E–G.Cheilocystidia. H–J. Morphology of A. malangelus (ZRL2012628): H–I. Basidiomata; J. Basidiospores. K–M. Morphology of A. pusillobulbosus (ZRL2012627, HOLOTYPE): K–L. Basidiomata; M. Basidiospores. Scale bar A–C, H–I, and K–L = 10 mm; D–G and J = 10 μm; M = 20 μm.

FIGURE 6. A–F. Morphology of A. melanocapus (ZRL2011037 HOLOTYPE): A–D Basidiomata, C shows yellow staining at the base of stipe; E. Basidiospores; F. Pileipellis hyphae. G–K. Morphology of A. nigrogracilis (ZRL2012014 HOLOTYPE): G. Basidiospores; H. Pileipellis hyphae; I–K. Basidiomata. Scale bar A–D = 20 mm; I–K = 10 mm; E–H = 10 μm.

FIGURE 7. A–C. Morphology of A. tytthocarpussp (ZRLWXH3077 HOLOTYPE): A. Basidiomata; B. Basidiospores; C. Pileipellis hyphae. D–G. Morphology of A. sinoplacomyces (ZRL2012008 HOLOTYPE): D–E. Basidiomata. F. Basidiospores. G. Pileipellis hyphae. H–K. Morphology of A. tibetensis (ZRL2012585, HOLOTYPE): H. Basidiospores; I. Pileipellis hyphae (in Congon red); J–K. Basidiomata. Scale bar A, D–E and J–K = 10 mm, B, C and F–I = 10 μm.