Trechispora onusta P. Karst. Hedwigia 29:147, 1890.

MycoBank number: MB 230699; Index Fungorum number: IF 230699, Facesoffungi number: FoF

= Polyporus hymenocystis Berk. & Broome, 1879  Trechispora hymenocystis (Berk. & Broome) K.H. Larss. Mycol. Res. 98: 1167, 1994.

Type specimen: Finland, Mustiala, in ligno Salicis capr., Oct. 1886, leg. P. Karsten. NY 776317 (http://sweetgum.

Remarks: Trechispora was introduced with a single spe- cies, T. onusta P. Karst. (Karsten 1890). The important fea- tures of the new species were poroid hymenophore, fragile consistency, and numerous rounded, aculeate, ca. 4 μm large basidiospores. The species has been mistaken for a species of Sistotrema, presumably because the type collection was mixed and that pieces of the specimen containing the foreign element were distributed to other mycologists. Rogers (1944) first chose the Sistotrema-like el- ement as lectotype but later corrected himself when he found material in Herbarium NY annotated by Karsten and fully conforming to the protologue, including date, place, and sub- strate (Rogers in Lowe 1956). Already, Romell (1911) was aware of the true identity of T. onusta and commented that two fungi were present in Karsten’s original collection. Romell identified the material containing ornamented spores as Polyporus hymenocystis Berk. and Broome.

Larsson (1992, 1994) used SEM to study basidiospores and calcium oxalate crystals in collections of poroid Trechispora species. He found that there are three species in North Europe and identified them as T. candidissima, T. hymenocystis, and T. mollusca after comparison with type material. The three species can be separated on spore morphology even if differences are small, but above all on crystal morphology. Larsson also studied the type of T. onusta and found that spore measurements and crystal morphology are in agreement with T. hymenocystis. This species is rather common in southern Finland where the type locality for T. onusta is situated. Trechispora candidissima is a northern species not found in southern Finland, while T. mollusca occurs in the whole of Finland, but is much rarer. Karsten (1890) described the ecology for T. onusta as “supra lignum mucidum Salix capreae.” This indicates a moist locality and strongly decayed wood. Such conditions do not fit the ecology of T. mollusca that is mostly found on branches and thin logs in mesic to dry forests. We have no doubt that T. onusta and T. hymenocystis are conspecific and that sequences of T. hymenocystis therefore represent the type species for Trechispora.