Laboulbenia triarthronis W. Rossi & M. Leonardi, sp. nov.

Index Fungorum number: IF 558362; MycoBank number: MB 558362; Facesoffungi number: FoF 09956; Fig. 1

Etymology – Referring to the host genus, Triarthron.

Holotype – SYRF RKB 601a

Thallus tinged with pale yellow, rather stocky, regularly enlarging from below upwards. Basal cell of the receptacle (cell I) slender, twice (or slightly more) longer than broad. Cell II slightly longer and distinctly broader than cell I, divided from cell III by a short transverse septum and from cell VI by a much longer, oblique and concave septum. Cell III broadly quadrangular, distinctly longer than broad. Cell IV about as long as cell III but broader. Cell V relatively large, shaped like an inverted tringle. Insertion cell oblique, narrow and thick, distinctly free from the perithecium. Basal cell of the outer appendage relatively large, longer than broad, bearing two branches in mature thalli; one of these branches is erect, relatively short, consisting of a linear series of small cells subtended by a contrasting blackish, constricted and elongate collarette; the second branch is produced after the former from the outer, upper angle of the basal cell: it is usually longer than the former and its cells are gradually longer towards the tip. In immature thalli the inner appendage consists of two superimposed subequal cells slightly longer than broad bearing distally a single, short antheridium, which is later displaced laterally by the growth of a branch longer than the branches of the outer appendage; sometimes this latter branch divides in two from the base. Cell VI longer than broad, irregularly shaped. Perithecium adnate to the receptacle for 2/3 to 3/4 of its length, slightly inflated, almost three times longer than maximum width, tapering without abrupt constriction to the truncate, dark brown tip slightly oriented outwards and ending in an almost flattened, hyaline apex. Length from foot to perithecial apex 190–300 µm; longest appendage 175 µm; perithecium 95–140 × 35–60 µm.

Material examined – USA, Illinois, Champaign Co., Brownfield Woods, 3 mi NE of Urbana, 14 August 1950, R.K. Benjamin, on all parts of the body of Triarthron lecontei Horn (=T. pennsylvanicum Horn) (Coleoptera, Leiodidae) collected on Armillariella mellea., (SYRF RKB 601a, holotype; SYRF RKB 601b, 601c, 601d, 601e, and FI WR4485, paratypes).

Notes – The appendages of Laboulbenia triarthronis easily distinguish the new species from the many others described so far (Fig. 1). As to the rest of the thallus, it might be compared with L. madeirae, described on a ground beetle, which however bears a single, robust and elongate outer appendage (Thaxter 1908, Plate LIV). Laboulbenia triarthronis is the first species of Laboulbenia reported on Coleoptera Leiodidae. The beetles of this family of insects are the hosts of the other 14 genera in the Laboulbeniales, 4 of which are found only on Leiodidae (Benjamin 1955; Rossi and Santamaria 2012; Haelewaters and Rossi 2017).

Figure 1 – Laboulbenia triarthronis (SYRF RKB 601a, holotype). a Thallus from the type slide stained with cotton blue. b Immature thallus from a paratype slide stained with cotton blue. Scale bars: a, b=50 µm