Agaricus rufusfibrillosus M.Q. He & R.L. Zhao.
Index Fungorum number: IF 553825; Facesoffungi number: FoF03627
Pileus 57–70 mm in diameter, at convex first, then broadly convex when mature, disc truncate, background white, margin straight; surface dry, completely covered by fibrillose scales, scales triangular, appressed, denser at the disc, scanty towards the margin, orange brown or brown, Context 5 mm thick, flesh, white. Lamellae 6 mm broad, free, crowded, normal, pinkish brown, edge even. Annulus 50 mm in diameter, fragile, membranous, single, white, pendant, upper side smooth, the lower side slightly floccus, with cortinate fibrils around the stipe. Stipe 51–80 × 11–20 mm, white, hollow, cylindrical with fusiform base; surface dry, with brown fibrils. Odour of almond. No discoloration when cutting. KOH reaction: positive yellow. Basidiospores 5.1–6.1 × 3.6–3.9 μm, (`x = 5.6 ± 0.2 × 3.8 ± 0.1, Q = 1.3–1.6, Qm = 1.5 ± 0.1, n = 20), ellipsoid, smooth, thick-walled, brown. Basidia 14.6–22.2 × 6.8–8.1 μm, clavate, hyaline, 4-spored, smooth-walled. Cheilocystidia absent. Pleurocystidia absent. Pileipellis a cutis composed of hyphae of 4.2–13.5 μm in diameter, smooth, cylindrical, light brown, not constricted at the septa.
Habitat: gregarious on soil at road side.
Material examined: CHINA, Zhejiang Province, Jingning County, Cao Yutang Forest Park, 19 August 2015, M.Q. He, ZRL 20151536 (HMAS 280110, holotype).
Notes: The simple annulus, positive yellow KOH reaction and almond odour of the basidiome confirm this new species is a member of subgenus Minores. In the phylogenetic analysis, it clusters with other two species A. fulvoaurantiacus L.J. Chen & Karunarathna and A. luteofibrillosus M.Q. He, L.J. Chen & R.L. Zhao with 100/1.0 BS/PP support in section Minores (Fig. 1). With respect to morphology, these three species roughly resemble each other, both in the field and under the microscope. In the field, they all have mid-sized basidiomes, brown or orange brown pilei and triangular scales on the caps. Under the microscope they all have the similar basidiospores. The main differences these two-new species to A. rufusfibrillosus are that the latter has a truncate disc, while the others lack a truncate disc, and the cheilocystidia are absent, but abundant in other species. Compared separately, A. rufusfibrillosus has a shorter stipe than A. luteofibrillosus (61–41 × 14 (base 8–25) mm, Li et al. 2016a), and white annulus on both sides, while in A. fulvoaurantiacus yellowish flakes are found on the lower side (Chen et al. 2017). There are many polymorphisms within the species A. fulvoaurantiacus and A. luteofibrillosus (Chen et al. 2017), we therefore compared the ITS region among the three species. Besides all the polymorphisms, there are also 13 positions of A. rufusfibrillosus that differ from these two species.
Fig. 1 Maximum likelihood (ML) tree of Agaricus subg. Minores based on ITS sequences with the outgroup Agaricus rufoaurantiacus. The bootstrap support values greater than 50% and Bayesian posterior probabilities greater than 0.9 are indicated at the nodes (BS/PP). The branches with Bayesian posterior probabilities greater than 0.95 are in bold. New species are in bold
Fig. 1 continued