Steccherinum perparvulum Hjortstam & Ryvarden

Steccherinum perparvulum Hjortstam & Ryvarden Figs 8 D, 9 D, 11 F Description. Full description in: Hjortstam and Ryvarden (2008). Mating system. Tetrapolar. Monosporic cultures obtained from specimens 710 / 20 and 742 / 23. Habitat and distribution. Widespread in southern to southeastern Brazil, mainly in high-altitude areas. Specimens examined. Brazil • Rio Grande do Sul: Nova Roma do Sul, ponte velha, 05 Apr. 2017, M. C. Westphalen 524 / 17 (SP 512658); • São Francisco de Paula, CPCN Pró-Mata, 17 May 2018, M. C. Westphalen 659 / 18 (SP 512661); • ibid., 22. Apr. 2023 M. C. Westphalen 744 / 23 (ICN 213878); • ibid., 19 Apr; 2024, N. C. Regio NR 186 (ICN 213879); • ibid., FLONA, 19 Apr. 2023, M. C. Westphalen 742 / 23 (ICN 213877); • Caxias do Sul, Parque da Gruta Nossa Senhora de Lourdes, 28 Mar. 2019, M. C. Westphalen 692 / 19; ibid., 09. Nov. 2020, M. C. Westphalen 710 / 20 (ICN 213876). • São Paulo: Moji-Guaçu, Fazenda Campininha, 29–30 Jan 1987, D. Pegler, K. Hjortstam & L. Ryvarden 24589 (O - holotype); • Parelheiros, Parque Estadual da Serra do Mar, Núcleo Curucutu, 16 Nov. 2016, V. Motato-Vásquez MV 815 (SP 512656); • São Paulo, Parque CIENTEC, 07 Jul. 2016, V. Motato-Vásquez MV 728 (SP 512657); • ibid., Parque Estadual Cantareira, Núcleo Engordador, Trilha da Cachoeira, 24 Apr. 2017, M. C. Westphalen 543 / 17 (SP 512659); • Santo André, Reserva Biológica do Alto da Serra de Paranapiacaba, 25 Aug. 2017, M. C. Westphalen 592 / 17 (SP 512660). Notes. This species is primarily distinguished by having the smallest basidiospores (2.3–3.1 × 1.7–2.2 µm) of all Neotropical hydnoid / odontioid Steccherinum, usually measuring under 3 µm long (Table 5). Macroscopically, it typically forms large basidiomes with short aculei and a papery consistency when dried. While most of the specimens examined were strictly resupinate, some exhibited small pilei along the margins. We examined the holotype of S. perparvulum and found several specimens with basidiospore sizes and general morphological characteristics consistent with the species. However, our phylogenetic analyses revealed that these specimens comprise at least three distinct lineages (Figs 1, 3). These lineages show minor differences in the ITS region, although subtle variations also occur among specimens within the same lineage (Fig. 12). To determine whether the genetic differences observed represent distinct biological species or reflect broader molecular variability within the ITS region of S. perparvulum, we conducted mating tests with monosporic cultures from three different specimens (Table 6). Two of these specimens belonged to the same lineage (710 and 744, lineage 1), whereas the third represented a different lineage (742, lineage 3). The mating tests showed positive results only between specimens of the same lineage, with clamp connections present in 11 of 12 monosporic pairings. In contrast, all confrontations with specimen 742 were negative, with only simple-septate hyphae present. This further supports the hypothesis that the observed molecular differences represent separate species within the group. Unfortunately, cultures from lineage 2 were not available for compatibility testing. Further studies incorporating additional monosporic cultures would be valuable to explore potential intercompatibility within the group, especially considering that lineage 2 is phylogenetically very close to lineage 1. While our studies corroborate at least two different species within S. perparvulum, no morphological or biogeographical evidence was found to support their segregation. Therefore, we chose to retain these taxa under the same name for the time being, treating it as a species complex. Considering their morphological and phylogenetic affinities, this approach aims to facilitate the taxonomy of the group rather than complicating it by increasing the number of species and adding morphologically indistinguishable taxa. In addition, at present, it is not possible to define which of the lineages represents S. perparvulum s. s. Sequences from the type specimen or the type locality could further elucidate this issue and help clarify the taxonomy of this species complex.