Tricholoma costaricense 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 : 38-39

Tricholoma costaricense Ovrebo, Hughes and Halling sp. nov. ( Figs. 1 , 4 , 5 )

Mycobank no.:—MB 827632

Diagnosis:—Characterized by the glutinous yellowish brown, olive brown to yellowish golden brown pileus and relatively large spores, and occurrence in Costa Rica. The colour of the pileus separates it from others in the complex of related species. The two collections form a well-supported clade based on ITS sequences.

Holotype:— COSTA RICA. San Jose Prov.: Jardín de Dota, ± 3.5 km W of Empalme , 9˚42’53” N, 83˚58’28” W, 8 July 2000, Halling 7997 ( USJ 72063 ; Isotype NY).

Etymology:—Named in honor of the country of Costa Rica where the fungus was collected.

Description:— Pileus 30–90 mm wide, rounded conic when young, sub-umbonate, plano-convex with a low umbo to plane with a low umbo when mature, surface glutinous to viscid, becoming dry with extreme age, radially rugulose, finely fibrillose to squamulose scaly under gluten, nearly black on disc and lightening to yellowish brown or olive brown (5E8–7–6–5–4) toward the margin, or yellowish golden brown (5D7–6–5) overall; context up to 8 mm thick, white, unchanging, with strong farinaceous odor and taste. Lamellae adnexed to emarginate, white to pale yellowish white (4A3,2), unchanging but gradually developing some brownish stains on edges with age or perhaps bruising, close, edges even or uneven. Stipe 40–120 mm long, 10–16 mm wide, equal but often slightly enlarged or tapered at the base, dry, the base sometimes curved, background color white, with conspicuous brownish to pale greenish yellow squamules almost to apex, white at apex; context pithy and becoming hollow, white, unchanging. Macrochemical color reactions:—PDAB bright maroon on interior portions of old stipe context (only REH 7997 tested).

Basidiospores 8–9.5 × 6–6.5 μm (mean=8.53 × 6.2 μm, Q=1.23–1.46, mean Q=1.37), elliptic to broadly elliptic in profile and face view, smooth, thin-walled, colourless, inamyloid. Basidia 33–43 × 8–10 μm, clavate, 4-sterigmate, colourless. Cheilocystidia 30–57 × 8–20 μm, cylindric, clavate or saccate, sometimes collapsed, smooth, thin-walled, colourless but lamellar edge light ochre brown when viewed under low power. Pleurocystidia absent. Lamellar trama composed of parallel colourless hyphae, 4–13 μm diam. Subhymenium hyphae 2.5–3.5 μm diam, colourless. Pileipellis as an ixocutis, hyphae radially interwoven or sometimes clumped in a gelatinous matrix that is thin in places especially on the margin, hyphae 3–5 μm diam, a mixture of colourless and translucent brown hyphae, smooth, thin-walled. Subcutis hyphae pseudoparenchymatous, cells 7–20 μm diam, cylindric to slightly inflated, yellowish ochre to dark dull brown as a layer, cells often with dark brown pigment deposits or incrustations in places. Pileitrama composed of colourless hyphae 5–15 μm in diam. Stipitipellis forming a thin to moderately thick (up to 100 μm) layer of appressed, yellowish ochre to cinnamon brown hyphae 3–5 μm diam, smooth, thin-walled, mainly translucent, with scattered hyphal clusters forming clumps that are ochre brown in mass, hyphae mainly translucent with entire clumps being opaque; surface hyphae at stipe apex 4–10 μm diam, interwoven, smooth, thin-walled, colourless or with scattered translucent yellow hyphae. Stipititrama composed of colourless hyphae 4–12 μm in diam. Clamp connections absent. Habitat:—Gregarious, on soil, under Quercus seemannii and Q. copeyensis .

Additional collections studied:— COSTA RICA. San Jose Prov.: Jardín de Dota, ± 3.5 km W of Empalme, 9˚42’53” N, 83˚58’28” W, 23 June 2003, Halling 8418 (USJ 81859, NY).

Discussion:— Tricholoma costaricense is characterized by the yellow brown to olive brown, viscid pileus, rugulose pileal surface, strong farinaceous odor and taste, presence of cheilocystidia, pseudoparenchymatous pileal subcutis and fairly large spores. The strong pink PDAB reaction noted on one collection is not typical for this species complex, but resembles the staining reaction of T. virgatum (Fr.) Kumm. (1871: 134) and related species. Tricholoma olivaceobrunneum can have olive tones but its pileal coloration has a stronger brown or gray aspect and lacks any yellowish brown coloration and it has smaller spores. Tricholoma subaureum also has some yellowish tones to the pileus but the pileus surface is dry and has smaller spores. The relatively large spore size is shared with T. atratum (see below) but that species has a dark gray dry pileus. Based on our phylogenetic analysis, T. costaricense is distantly related to T. mutable , T. marquettense and T. felschii and is more closely related to T. fucatum ( Figure 1 ), a European species but with only 85% ITS sequence homology.

Figures

FIGURE 1. PhyML analysis of the nuclear ribosomal ITS region. Collection locations where known are given by the US Postal code for states. GSM=Great Smoky Mountains NationalPark,Tennessee side; BC=Canada British Columbia; CR=Costa Rica; ENV=environmental sequence. Ecto=ectomycorrhizal root tip. Bootstrap values are given to the left of the supported node. Percent divergence calculations were calculated using all base pair differences (i.e., a 13bp insertion in CLO3549 and AGF21 was counted as 13 bp differences, not a single difference).

FIGURE 4. Basidiomes. Tricholoma costaricense, holotype, both photos same collection, Halling 8418. Photos by R.E. Halling. Scale line = 20 mm.

FIGURES 5. Basidiomes. Tricholoma atratum. A. Halling 8263, holotype. B. Halling 8158. Photos by R. E. Halling. Scale line = 20 mm.