Siderais a polypore genus with white to cream or buff basidiomata, whose species in Hymenochaetales are poorly known. We study the phylogeny and diversity ofSiderabased on our recent collections from tropic and subtropic Asian-Pacific regions. Phylogenetic analyses based on the internal transcribed spacer (ITS) and nuclear large subunit (nLSU) ribosomal RNA gene regions indicate that ten terminal lineages are well supported withinSidera. Based on morphological examination and phylogeny, four new species, viz.Sidera minutissima,S. parallela,S. srilankensisandS. tenuisare described, and a new combination,Sidera minutipora, is proposed. All these species are illustrated.Sidera minutissimais characterized by tiny basidiomata with bluish pores when fresh, generative hyphae dominating at the dissepiment edges, the presence of cystidioles, and allantoid basidiospores measuring 3.8–4.4 × 0.9–1.3 μm.Sidera paralleladiffers from other poroid species in the genus by having parallel tramal hyphae in combination with lunate basidiospores measuring 2.8–3.3 × 0.9–1.2 μm.Sidera srilankensishave generative and skeletal hyphae co-dominating at the dissepiment edges, and lunate basidiospores measuring 3.5–4 × 1–1.3 μm.Sidera tenuisis distinguished by small pores (8–10 per mm) and relatively long allantoid basidiospores measuring 4.2–5 × 0.8–1 μm.Sidera minutiporais characterized by buff to olivaceous buff basidiomata when dry, 5–7 pores per mm, rosette-like crystals rare, and allantoid basidiospores measuring 3.7–4.3 × 1–1.3 μm. An identification key to all accepted species is provided.
