Rostrupomyces Vadthanarat & Raspe, 2024

Vadthanarat, Santhiti, Raghoonundon, Bhavesh, Lumyong, Saisamorn & Raspe, Olivier, 2024, Rostrupomyces, a new genus to accommodate Xerocomus sisongkhramensis, and a new Hemileccinum species (Xerocomoideae, Boletaceae) from Thailand, MycoKeys 103, pp. 129-165 : 129

Rostrupomyces Vadthanarat & Raspe gen. nov.

Etymology.

Named in honor of Frederik Georg Emil Rostrup (1831-1907), Danish botanist, mycologist, and plant pathologist, celebrating the 120 years of his describing the first new species of Boletaceae from Thailand in 1902.

Diagnosis.

Differs from other genera in Boletaceae by the following combination of characters: rugulose to subrugulose pileus surface, white pore when young becoming grayish yellow in age, subscabrous stipe surface with scattered granulose squamules, white basal mycelium, unchanging color in any parts, yellowish brown spore print, and broadly ellipsoid to ellipsoid, smooth basidiospores.

Description.

Basidiomata stipitate-pileate. Pileus convex then plano-convex to plane; surface at first rugulose then subrugulose in age, finely tomentose to tomentose, dark brown to reddish brown, becoming light brown to brown to grayish orange, unchanging when bruised; context off-white then yellowish to dull pale orange in age, unchanging when cut. Stipe central, terete, cylindrical; surface subscabrous, yellowish white to pale yellow to orange white, with scattered brown to dark brown to reddish brown granulose squamules, unchanging when bruised; basal mycelium white; context solid, white becoming off-white to yellowish white in age, unchanging when cut. Hymenophore tubulate, slightly depressed to depressed around the stipe. Tubes pale yellow then grayish yellow, separable from the pileus context, unchanging when cut. Pores roundish then subangular to angular with age; when young white then yellowish white becoming grayish yellow, unchanging when touched. Spore print yellowish brown. Basidiospores ellipsoid to broadly ellipsoid, thin-walled, smooth under light microscope and SEM. Basidia 4-spored, clavate without basal clamp connection. Cheilo - and pleurocystidia narrowly fusiform to fusiform or narrowly utriform, thin-walled. Pileipellis an intricate trichoderm, made of moderately interwoven to loosely interwoven, thin-walled hyphae. Stipitipellis arranged parallel to the surface of the stipe, composed of moderately interwoven, thin-walled hyphae, with scattered groups of rising cells to clusters of narrowly clavate to clavate cells. Clamp connections not seen in any tissue.

Typus generis.

Rostrupomyces sisongkhramensis (Khamsuntorn, Pinruan & Luangsa-ard) Vadthanarat, Raghoonundon & Raspé.

Distribution.

Currently known only from northern and northeastern Thailand.

Notes.

Rostrupomyces can be morphologically separated from Xerocomus by the different shape and surface of basidiospores, which are ellipsoid to broadly ellipsoid with smooth under light microscope and SEM in the new genus, whereas Xerocomus produce more or less oblong to fusiform basidiospores, usually with bacillate surface under SEM ( Wu et. al. 2016). Rostrupomyces also produces yellowish brown spore print, whereas Xerocomus produces olive-brown spore print. Moreover, color change upon bruising does not occur in any part of Rostrupomyces basidiomes, whereas context and hymenophore of Xerocomus always turn more or less bluish to blue when bruised or cut ( Wu et. al. 2016). The most resembling genus, Hemileccinum , shares some similar characters including rugulose to subrugulose pileus surface, yellow hymenophore which is depressed around the stipe apex, subscabrous stipe surface (less so in Hemileccinum ), white basal mycelium, mostly unchanging color in any parts. However, Rostrupomyces can be morphologically distinguished from Hemileccinum by the differences in spore print color, and in the shape and surface of basidiospores. Rostrupomyces produces yellowish brown spore print, broadly ellipsoid to ellipsoid basidiospores with smooth surface under light microscope and SEM. Hemileccinum produces olive-brown spore prints, boletoid basidiospores that are smooth under light microscope, but ornamented with irregular warts and pinholes under SEM. Also, the pore surface of Rostrupomyces is white in young basidiomata and becomes pale yellow when mature whereas in Hemileccinum , the pore surface is yellow in all stages ( Šutara 2008; Wu et al. 2016; Farid et al. 2021; Li et al. 2021).