Albatrellus subrubescens Pouzar, Ceska Mykol.

Albatrellus aff. subrubescens (Murrill) Pouzar, Česká Mykol. 26: 196 (1972)

Basidiomes medium-sized, stipitate (Fig. 2). Pileus 35–50 mm in diameter; surface off-white to pale ochraceous, with faint pinkish hues at places when fresh, discoloring yellow when bruised, dull, dry, minutely and densely felted; margin inflexed becoming reflexed, irregular at places, with 1–3 clefts. Pileus context 7–8 mm thick at the centre of pileus, 3–4 mm thick half-way to the margin, slightly thinner at the margin, unchanging when bruised. Stipe excentric, cylindrical, 25–30 × 4–7 mm, white to yellowish white, with white basal tomentum and rhizoids. Surface even, dull, dry, minutely and densely tomentose, slightly orange when bruised. Stipe context solid. Tubes 0.5–1 mm long, deeply decurrent at least on one side of the stipe, yellowish white. Pores irregular, 0.3–1.5 mm in diameter, regularly arranged, white, dry. Odor aromatic; taste not recorded.

Basidiospores (Fig. 3) (3.5–)3.7–4–4.4(–4.5) × (3–)2.7–3.1–3.5(–3.5) μm, Q = (1.14–)1.15–1.3–1.45(–1.5) {N = 55}, broadly ellipsoid, smooth, thin-walled, mostly with one large drop, hyaline in 5% KOH, amyloid (bluish grey in Melzer reagent). Basidia 4–spored, (18–)16.7–20.8–24.9(–27) × (6–)5.7–6.3–6.9(–7) μm {N = 20}, clavate, hyaline in 5% KOH, yellowish in Melzer reagent, without basal clamp connection; sterigmata 3–4 μm long, slightly curved. Pleurocystidia and cheilocystidia absent. Hymenophoral trama subregular, 35–65 μm wide. Pileipellis (Fig. 3) 45–65 μm thick, with repent hyphae composed of slightly thick-walled and slightly amyloid, cylindrical to irregular, 6–54 × 3–7 μm elements, with very small incrustations on the walls, and yellowish brown content in Melzer reagent. Pileus context composed of slightly thick-walled, 4–14 μm wide hyphae with scattered, very small incrustations on the walls. Stipitipellis 65–85 μm thick; terminal cells 8–45 × 3.5–9 μm, slender to slightly swollen, with roundish apex; cell wall 0.5–1.5 μm thick, amyloid, with scattered incrustations; content yellowish brown in Melzer reagent; caulocystidia not seen. Stipe context composed of slightly thick-walled and slightly amyloid, 5–15 μm wide hyphae. Clamp connections not seen in any tissue.

Ectomycorrhizae (Fig. 4) development dichotomous, with either only a few ramifications or many (coralloid development); axes ca. 0.2–0.35 mm across, mostly black to dark brown, covered with short hairs; extremities sometimes covered by a white layer, which may represent the initiation of basidiomes.

Ecology: Road verge in mixed forest with Pinus kesiya, Carpinus poilanei, Betula alnoides and Lithocarpus spp. Ectomycorrhizal with P. kesiya.

Material examined: THAILAND, Chiang Mai Province: Meuang District, Doi Suthep-Pui National Park, elev. 1,590 m, N 18°49’00” – E 098°53’36”, 16 July 2015, Olivier Raspé 996 (SDBR-CMU OR996, BR5020187498846).

Remarks: Following the keys provided by Zheng & Liu (2008) and Audet (2010), our material was identified as Albatrellus subrubescens. However, the protologue of A. subrubescens (Murrill 1940) present a number of discrepancies with our material. Basidiomes are larger (pileus 6–9 cm across, stipe 1–2 cm in diameter), and the pileus is said to be decorated with erect, dark-colored, tufts of fibrillose squamules that are conspicuous on the disk. Moreover, the pores are described as ‘circular to slightly angular’, and very small (4–5 per mm). Unfortunately, neither Zheng & Liu (2008) nor Audet (2010) provided a detailed description of the species. The description given by Ginns (1997) of North American material, also mentioned larger basidiomes (‘pileus to 10 cm in diameter), and ‘some [pileus] covered with blackish grey to purple-grey fibrils’, but only 2–3 pores per mm. Ginns (1997) also mentioned ‘faint rosy buff tints centrally, and yellow stains where handled’, which we observed in our material. However, Ryman et al. (2003) used the yellow discoloring of the pileus surface as a diagnostic characteristic to distinguish A. citrinus from A. subrubescens, the latter being said to stain orange. Therefore, it is unclear whether the discrepancies between the protologue of A. subrubescens and our material are compatible with within-species variation or if the variation described by various authors results from the inclusion of material of different species.

The morphology of Pinus kesiya / Albatrellus aff. subrubescens ectomycorrhizae we observed can be compared to the Picea abies / Albatrellus ovinus ectomycorrhizae described by Agerer et al. (1996). Both are similar in color, but also show marked differences. While the latter show monopodial growth and abundant rhizomorphs, dichotomous growth and only rare or no rhizomorphs were observed in the former. However, rhizomorphs may have been lost in the cleaning process.