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Agaricus subtilipes

Agaricus subtilipes Thongkl., Linda J. Chen, Callac & K.D. Hyde 

Index Fungorum number: IF550767, Mycobank: 550767, Facesoffungi number: FoF 00598

Pileus 4-9 cm diam, thin, hemispherical then convex finally applanate, sometimes umbonate at the disc surrounded by a hardly depressed peridiscal zone, covered with grayish-brown to light brown appressed squamules, dense and triangular at disc which can also remain unbroken, and sparse, dot-like or minutely triangular outside the disc on a white to cream background, becoming yellowish when bruised. In young sporophores, unfrequently when mature, broad membranous white or pale brown patches coming from the universal veil can be observed near the margin; pileal surface smooth, dull and dry; margin straight, not or slightly exceeding the lamellae, radially splitting when mature or in dry condition. Lamellae free, crowded, and narrow, light pink when young then light brown and dark brown with age, 2–5 mm broad. Stipe 6.7–10 × 0.4–1 cm, 0.8–2 cm at the bulb, often curved, hollow, cylindrical and bulbous to abruptly marginate bulbous at the base, provided with an annulus, above the annulus white and smooth, below covered with small white floccose squamules, provided with copious rhizomorphs. Annulus superous, attached to the upper part of the stipe, pendent, double: upper layer membranous, lower layer white becoming yellowish with time or age, more or less densely floccose squamulose, discoloring yellow after bruising. Context firm, thick, white when young, color not recorded in mature sporophores. Odor almond-like or aniseed. Chemical reactions: KOH reaction positive yellow; Sch€affer's reaction positive orange. Microscopical characters: Basidiospores (4.2) 4.6–5.0–5.7(5.8) × (2.4)3.3–3.4–4.0(4.5) mm; Q = 1.2–1.5–1.8 [N= 80, from 4 specimens], ellipsoid with 1 or 2 guttules, thick walled, brown in KOH with dark brown walls, smooth with a prominent apiculus. Basidia 11.5–17.6 × 5.1–7.8 mm, clavate, tetrasporic, hyaline in KOH. Cheilocystidia 5.1–14.5 × 3.9–13.3 mm, hyaline and smooth, abundant, in clusters, broadly clavate to globose, single or catenulate up to three cells. Pleurocystidia absent. Pileipellis a cutis constituted by cylindrical hyphae containing brown vacuolar pigment, smooth, straight, cylindrical, 2.1–5 mm in diam. Clamp connections absent. (Figs. 1–2)

Etymology: in reference to the long and slim stipe.

Holotype: THAILAND, Chiang Rai province, Mae Fah Luang University, on litter, 14 May 2012, J. Chen, LD201201 (MFLU120847, holotype; ITS GenBank accession number KP705078).

            Habitat: Gregarious in grassy areas or in leaf litter; sometimes forming fairy rings.

Specimens examined: THAILAND, Chiang Rai province, Mae Fah Luang University, on litter, 14 May 2012, J. Chen, LD201201 (MFLU120847, holotype; ITS GenBank accession number KP705078). FRANCE, Bordeaux, cultivated specimen at INRA, 18 Dec 2012, sporocarp from isolate LD201201 (MFLUCC 140478); THAILAND, Chiang Rai province, Mae Fah Luang University, fairy rings in grass, 13 Jun 2011, P. Callac & S. Rapior, CA915 (MFLU140223; ITS GenBank accession number KP705077); Mae Fah Luang University, in grass, 15 Jun 2011, P. Callac, S. Karunarathna & S. Rapior, CA920 (MFLU140216; ITS GenBank accession number KJ787015); Mae Fah Luang University, on litter, 2 Aug 2012, J. Chen, LD2012164 (MFLU120992; ITS GenBank accession number KP705079).

Distribution: Known only from northern Thailand.

Notes: Agaricus subtilipes shares characteristic traits with species of A. sect. Arvenses: a double annulus, positive KOH and Schaffer € 's reactions, an almond-like or aniseed odor and catenulate cheilocystidia. Moreover, the new species is characterized by brownish appressed triangular squamules on the pileus surface, a slender stipe covered with small white floccose squamules below the annulus and, relatively smallsized spores. The sequences of the ITS1þ2 region of the four collections of A. subtilipes differ at the two polymorphic positions 178 (T, C, or C/T heteromorphism) and 614 (A or G). This level of polymorphism is frequent within Agaricus species. Among the used samples, Agaricus subtilipes is characterized by the five species specific ITS markers mentioned above. The fruiting bodies of A. subtilipes are variable depending on environmental conditions.