Afroboletus sequestratus L.H. Han, Buyck & Zhu L. Yang, 2017

Han, Li-Hong, Buyck, Bart, Yorou, Nourou S., Halling, Roy E. & Yang, Zhu L., 2017, Afroboletus sequestratus (Boletales), the first species with sequestrate basidioma in the genus, Phytotaxa 305 (1), pp. 11-20 : 15-16

1. Afroboletus sequestratus L.H. Han, Buyck & Zhu L. Yang , sp. nov. Figs. 2 , 3a, 3b

MycoBank:—MB 819800

Etymology:— sequestratus is proposed because of its sequestrate basidioma.

Type:— Zambia. Road Mpongwe-Luanshya, regenerating forest on former agricultural land, 2. Feb. 1996, B. Buyck 96271 (PC 0723575! Images of the type: http://sweetgum.nybg.org/science/projects/boletineae/taxon-details/?irn=1441899).

Description:— Basidioma hypogeous to emergent, sequestrate, stipitate. Pileus hemispheric, convex, 6–7 cm in diam.; upper surface dirty white to greyish or brownish but becoming brownish then blackish when bruised, glabrous or locally covered with repent to slightly reflexed, dark brown to blackish squamules; lower surface brownish to brown. Gleba greyish to brownish grey, staining brown when cut, then blackish slowly, mostly longitudinally loculate; locules 1–2 mm broad; columella present, greyish to brownish, staining brown when cut, then blackish slowly. Stipe 5 × 2– 1.5 cm, attenuate upwards, dirty white, pale grey to brownish, nearly smooth, covered with grey to brown to blackish floccose squamules; annulus present, but easily broken; context dirty white to brownish, becoming brown to blackish when injured.

Basidiospores [20/1/1] (10.5)11–14 × 9–11 μm [Q = (1.09)1.11–1.37(1.40), Q m = 1.21 ± 0.01], orthotropic, statismosporic, broadly ellipsoid to ovoid in equatorial view excluding ornamentation, yellow-brown, brown to cinnamon brown, thick-walled (up to 2.5 μm thick); ornamentation of 10–13 solid costae mostly regularly and longitudinally arranged and extending over the spore length, occasionally shorter and anastomosing, up to 2 μm tall, giving the spores a stellate appearance in polar view; hilar appendix with a basal thickened rim 2–3 μm in diam.; suprahilar plage not present. Basidia 30–35 × 14–17 μm, clavate, 4-spored; sterigmata stout, straight, 7–8 μm long. Cystidia present, 45–65 × 18–22 μm, subfusiform, thin-walled, colorless or with yellow-brown contents. Tramal plates composed of thin-walled, non-gelatinized to gelatinized, colorless or brownish filamentous hyphae 2–7 μm broad. Pileipellis a cutis composed of radially arranged, brown to dark brown intracellularly pigmented, slightly thick-walled (ca. 0.5 μm thick) filamentous hyphae 2–7 μm broad; outer surface of pileipellis locally covered with irregularly to subvertically arranged, thin-walled, 3–10 μm broad, intracellularly brown to dark brown pigmented filamentous hyphae aggregating into squamules on pileal surface, terminal cells cylindrical to narrowly clavate, 30–60 × 5–12 μm. Stipe trama composed primarily of longitudinally arranged, branching, thin-walled, colorless and hyaline or brownyellow intracellularly pigmented filamentous hyphae 3–10 μm broad. Clamp connections absent.

Habitat and distribution:—Solitary to scattered on laterite rich soil; fruiting in spring; only known from type locality.

Figures

FIGURE 2. Morphological characters of Afroboletus sequestratus (PC 0723575, type). a. Basidioma in vertical section; b. Basidiospores in polar view (left) and equatorial view (right); c. Basidia and basidiospores at different stage of development, and a cystidium. Bars a = 2 cm, b and c = 10 μm. Drawings by Zhu L. Yang.

FIGURE 3. Ornamentation of basidiospores of Afroboletus and Strobilomyces. a. Afroboletus sequestratus (PC 0723575, type), showing the longitudinal costae; b. Afroboletus sequestratus (PC 0723575, type), showing the hilar appendix with a basal rim (arrow); c. Afroboletus multijugus (PC 0723570), showing the longitudinal costae, the basal rim (arrow) around the apiculus and the non-differentiation of a suprahilar plage; d. Afroboletus luteolus (SYN 1836), showing the longitudinal costae, the basal rim (arrow) around the apiculus and the absence of a suprahilar plage; notice that a secondary surface ornamentation of longitudinal ridging with occasional branching is present between the costae; e. Strobilomyces pteroreticulosporus (HKAS 91274), showing the reticulate ornamentation, and the presence of a suprahilar plage (arrow); f. Strobilomyces seminudus (HKAS 59461), showing the subcristate to verrucose ornamentation, and the presence of a suprahilar plage (arrow). Bars = 2 μm. Photos by L.H. Han.