Tricholoma atratum Ovrebo, Hughes and Halling, 2019

Ovrebo, Clark L., Hughes, Karen W. & Halling, Roy E., 2019, Three new species of Tricholoma from Costa Rica, Phytotaxa 392 (1), pp. 33-44 : 40-42

publication ID	https://doi.org/ 10.11646/phytotaxa.392.1.3
persistent identifier	https://treatment.plazi.org/id/03EA8780-8430-FF92-FF47-CC53FAC3FE09
treatment provided by	Felipe
scientific name	Tricholoma atratum Ovrebo, Hughes and Halling
status	sp. nov.

Treatment

Tricholoma atratum Ovrebo, Hughes and Halling View in CoL sp. nov. ( Figs. 2 View FIGURE 2 , 5 View FIGURES 5 , 7 View FIGURE 7 )

Mycobank no.:—MB 827633

Diagnosis:—Characterized by the dark gray dry pileus, lack of cheilocystidia, presence of pileocystidia, relatively large spores, and occurrence in Costa Rica.

Holotype:— COSTA RICA. Cartago Prov.: El Guarco, Tapanti, Parque Nacional Tapanti, Macizo de la Muerte, 9˚41’6” N, 83˚52’30” W, 2600 m: 6 July 2001 Halling 8263 ( USJ 109186 About USJ ; Isotype NY).

Etymology:—From Latin atratus meaning dark, black, clothed in black; referring to the dark gray to black coloration of the pileus.

Description:— Pileus 40–80 mm wide, convex to plano-convex, sometimes with a low umbo, dry, appressedfibrillose, becoming radially rugulose often with some moisture loss, black on disc and dark gray toward margin or dark gray overall, with undertones of pale greenish yellow; context 7 mm thick (on one collection) white to pale watery gray, unchanging, odor and taste farinaceous. Lamellae adnexed-emarginate, broad, grayish yellow (4A3, 4B4), close, edges even to uneven. Stipe 70–110 (150) mm long, 6–13 mm wide, equal but sometimes tapered or enlarged at base, fibrillose, whitish with pale gray tints, some staining slightly orangish brown from handling with age, white at base and often matted-fibrillose, context becoming hollow, white, unchanging. Macrochemical color reactions:— no reaction with PDAB.

Basidiospores 8–9(–9.5) × 6–7.5 μm (mean=8.53 × 6.54 μm, Q=1.21–1.42, mean Q=1.3), elliptic, broadly elliptic to subovate in profile and face views, smooth, thin-walled, colourless, inamyloid. Basidia 39–50 × 6–10 μm, 4- sterigmate, clavate, colourless, many with granular-guttulate contents. Hymenial cystidia absent. Lamellar trama hyphae 4–10 μm diam, parallel, pale yellow. Subhymenium composed of hyphae 2.5–3 μm diam, colourless. Pileipellis as a cutis, hyphae radially arranged to slightly interwoven, not embedded in a gelatinous matrix, 3–8 μm diam, cylindric to slightly inflated, smooth or roughened and thickened with brownish incrustations, the outer wall surface sometimes fracturing to form bands of varying pigment intensity, colourless to brown, brown as a layer. Pileocystidia scattered, formed by recurved end-cells, 22–37 × 5–13 μm, cylindric to clavate, occasionally two-celled, brown. Subcutis composed of pseudoparenchymatous hyphae, cells 12–23 μm diam, broadly inflated, cells of the layer often collapsed and the layer is then difficult to discern, colourless to brown as a layer. Pileitrama made up of hyphae 4–12 μm diam, pale yellow. Stipitipellis made up of hyphae 3–5 μm wide, appressed or sometimes clumped or entangled in places, smooth, thin-walled, very pale yellow. Stipititrama hyphae 4–14 μm diam, parallel, pale yellow. Clamp connections absent.

Habitat:—Gregarious, on soil, under Quercus copeyensis and Q. seemannii .

Additional collections studied:— COSTA RICA. San Jose Prov.: San Gerardo de Dota, ± 5 km SW of Cerro de la Muerte, Albergue de la Montaña, Savegre , 9˚32’02” N, 83˚48’27” W, 2200 m, 10 July 2000, Halling 8008 ( USJ 72083 About USJ ; NY), 9 June 2001, Halling 8158 ( USJ 74107 About USJ ; NY) .

Discussion:— Tricholoma atratum is characterized by the dark gray, dry pileus, farinaceous odor and taste, pseudoparenchymatous pileal subcutis, lack of cheilocystidia, presence of scattered pileocystidia, and relatively large spores. The yellowish undertones on the pileus surface and grayish yellow pigmentation of the lamellae may also serve as distinguishing features of this species. The recurved end cells of the pileus surface we interpret as pileocystidia ( Figure 7 View FIGURE 7 ). Pileal surface hyphae can be recurved in Tricholoma species but they are usually clumped and represent macromorphologically the surface squamules.

The rugulose pileus, farinaceous odor and taste and pseudoparenchymatous subcutis are features that T. atratum shares with the other taxa described here as well as taxa found in Ovrebo (1986) and several species included in Shanks (1997), so the initial hypothesis was that species sharing these characteristics would all be related. For many of the putatively related taxa found in these publications, sequence data are not yet available so molecular comparisons can only be made among a few species. It now appears unlikely, however, that T. atratum is closely related to the phenotypically similar taxa as shown in Figures 1 View FIGURE 1 & 2 View FIGURE 2 . The phylogeny in Figure 1 View FIGURE 1 shows a close relationship between T. mutabile ( Shanks 1997) , T. marquettense ( Ovrebo 1986) , T. felschii and the European T. josserandii , but T. atratum does not cluster with these taxa. Rather, Figure 2 View FIGURE 2 indicates a relationship of T. atratum with the European T. orirubens Quél. (1873: 327) , T. squarrulosum Bres. (1898: 47) and T. atrosquamosum Sacc. (1887: 104) . According to the descriptions provided by Christensen & Heilmann-Clausen (2013), the latter species have smaller spores, the subcutis is poorly differentiated and their pilei tend to be squamulose.

Based on morphological features, T. atratum differs from species treated by Ovrebo (1986) by the darker pileal coloration, the lack of cheilocystidia and the larger spores. Of the species treated by Shanks (1997), T. nigrum Shanks & Ovrebo (1996: 500) also has a dark gray pileus, but it possesses cheilocystidia, a pileipellis as an ixocutis and the spores are smaller. Tricholoma felschii has a dark gray pileal coloration, but has cheilocystidia and the pileipellis is an ixocutis. Tricholoma pullum Ovrebo (1989: 3139) and T. atrodiscum Ovrebo (1989: 3140) have dark gray pilei, but possess cheilocystidia, have a bitter to acrid taste and lack the pseudoparenchymatous subcutis. The dark pileus and yellowish tones of the lamellae are found in T. portentosum (Fr.) Quél. (1873: 338) , but the latter is viscid, has stronger yellow coloration to the pileus and stipe, lacks the pseudoparenchymatous subcutis and the spores are smaller.