Xerocomus longistipitatus K. Das, A. Parihar, D. Chakr. & A. Baghela

MycoBank: MB 818786

Type: India, Sikkim: East District, Rabangla, alt. 1985m, N27°15’14.8’’ E88°23’03.7’’, 22nd August, 2016, K. Das, A. Parihar & D. Chakraborty, DC 16-056 (holotype: CAL 1394; isotype: BSHC 50467)

Diagnosis: distinct from closely allied Xerocomus doodhcha, another Indian species, in having a significantly long stipe, a yellow context turning pale yellow then greyish turquoise on exposure and an ixotrichoderm-type pileipellis
Etymology: longistipitatus (L.) with a long stipe; referring to the long stipe of this species. Pileus 42–85 mm diam., initially convex, then planoconvex; surface dry, matte to subvelvet-like, brown (6D7–8) at the centre, paler towards the margin; margin entire, decurved with a narrow flap of tissue. Pore surface primrose yellow (1A6), bruised areas slowly turning greenish grey to dull green (26B2–3); pores rounded to angular or irregular, mostly simple, rarely compound, 1/mm. Tubes adnate to subdecurrent, 4–5.5 mm long, concolorous with the pore surface. Stipe 70–185 × 10–24 mm, mostly cylindrical, pale yellow to pastel yellow (2A3–A4) at upper half, then pale orange (5A3); surface longitudinally fibrillose. Context 15 mm thick in pileus, milk white (1A2), slowly becoming pale yellow (1A3), then greyish green (25B3); stipe context concolorous but at lower half of stipe, pale orange to greyish orange (5A3–B3) or paler. Pileus surface initially greyish turquoise (24D3–D4) then darker in NH4OH and no reaction in FeSO4. Spore print olive-brown (4D3). Basidiospores 10.8–12.6–14.6 × 3.6–4.2–4.5 μm, (Q 2.64–3.05–3.46), ellipsoidal to elongated to fusiform, inequilateral, thin-walled, smooth under light microscope, bacillate under SEM . Basidia 31– 45 × 9–13 μm, four-spored, clavate. Pleurocystidia 37–63 × 8–14 μm, emergent up to 30 μm, fusoid to ventricose, appendiculate, often cylindrical thin-walled with somewhat dense granular content. Subhymenial layer up to 10 μm thick, pseudoparenchymatous. Tube edge fertile with basidia and cystidia; cheilocystidia 26–34 × 8–10 μm, common, clavate; contents same as pleurocystidia. Hymenophoral trama phylloporoid, hyphae septate, gelatinous, up to 10 μm wide. Pileipellis an ixotrichoderm, up to 210 μm thick, composed of erect hyphae of slightly inflated cells; terminal cells 25–51 × 10–16 μm, cylindrical to subcylindrical, sometimes subfusoid, content brown pigmented. Stipitipellis up to 50 μm thick, fertile near the apex of stipe, composed of basidioles and cystidia in several clusters; basidia not observed; caulocystidia 30–36 × 10–12 μm, broadly clavate to subclavate.

Material examined – India, Sikkim: East District, Rabangla, on soil, under Lithocarpus sp., alt. 1985m, N27°15’14.8’’ E88°23’03.7’’, 22nd August, 2016, K. Das & D. Chakraborty, DC 16-56

Notes – Morphologically, X. longistipitatus can be confused in the field with another Indian species, Xerocomus doodhcha (89% identity in BLAST search) but the latter has distinctly shorter stipe (50–68 mm), a trichoderm-type (never ixotrichoderm) pileipellis and a context which turns orange white when exposed (Das et al. 2016). Three more species, X. subtomentosus (Fries) Quélet (reported from Europe), X. chrysonemus A.E. Hills & A.F.S. Taylor (reported from Europe) and X. illudens (Peck) Singer (reported from North America), which either appered in BLAST search, are somewhat close to X. longistipitatus (DC 15-056), but X. subtomentosus (showing 83–84% identity in BLAST search and represented by GenBank accession numbers DQ066364, DQ066365, DQ066366, DQ066367, DQ066369, DQ066370, KC215201 and JQ967281) differs from X. longistipitatus in having longer (10.5–15.2 μm) basidiospores, an olive brown to olive yellow pileus, a shorter (40–100 mm) stipe, slight bluing of the exposed context and turning of the pileus surface to ‘mehogony’ color with NH4OH (Smith & Thiers 1971). Xerocomus chrysonemus (represented by GenBank accession numbers DQ438141, DQ066379, DQ066381, DQ066385 and DQ066373) can easily distinguished from X. longistipitatus by a yellow ochre to yellow olive or greyish tawny pileus, a much shorter stipe (30–50 mm) with incomplete reticulations on surface, a context not changing to blue, smaller basidiospores (9–12.5 μm) and a trichoderm-type pileipellis (Janda et al. 2013). Similarly, .X. illudens (showing 96% query coverage with 87% identity in BLAST search and represented by GenBank accession number JQ003658) has a distinctively shorter stipe (30–90 mm) with longitudinal rib- like striations, an unchanging context (when exposed) and a trichodem-type pileipellis (Bessette et al. 2010). Another European species, X. silwoodensis (84% identity in BLAST search and represented by GenBank accession numbers DQ438142–DQ438145 and DQ066375) can easily be separated by its rusty brown to brown or dark brown pileus with rich bronze to red brown shades, a shorter stipe (25–70 mm) and an unchanging context color (on bruising), shorter basidiospores (9–13 μm), trichoderm nature of pileipellis and association with Populus sp. (Janda et al. 2014). Thus, both the morphological features and the ITS-based phylogeny corroborate the novelty of X. longistipitatus.

Phylogram generated from ITS-rDNA sequences: The evolutionary history was inferred by using the Maximum Likelihood method based on the Kimura 2-parameter model [1]. The tree with the highest log likelihood (-2596.3045) is shown. The novel species DC 16-056 (Xerocomus longistipitatus) having GenBank Accession Number KY008398 is shown in bold and blue. The Boletus edulis was considered as the out group. Evolutionary analysis was conducted in MEGA6 (Tamura et al. 2013)

Xerocomus longistipitatus (from holotype, DC 16-056). 2 & 4 Fresh basidiomata in the field and base camp. 3 Pore surface. 5 Transverse section through tube showing trama. 6 pleurocystidia. 7 Transverse section through tube edge showing cheilocystidia. 8 & 9 Radial section through pileipellis showing elements of pileipellis. 10 Caulocystidia. 11 Basidiospores. Bars 5, 7–9 = 50 μm. 6, 10–11 = 10 μm.