Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Important Taxonomic Note: The description below was originally published for "Acarospora succedens" in the Lichen Flora of the Greater Sonoran Desert Region, selecting a specimen at ASU as the neotype at the time, assuming all type material was lost. When the author (Knudsen 2011) subsequently discovered isotype material at FH the selection of that neotype became obsolete. From studying the isotype material the author concluded that his previous concept of A. succedens was erroneos and that this name instead had to be applied to A. interspersa, which is consequently now treated as a synonym of A. succedens.
The material originally considered as the "neotype" of A. succedens was then re-designated as the holotype of the new secies A. nashii(Knudsen 2011), to which the description below belongs:
Thallus: areolate, emerging from areoles of Dimeleana oreina or independent but scattered or forming small patches up to 2 cm across among areoles of D. oreina; areoles: mostly 0.5-0.8 mm wide, less than 0.4 mm thick, mostly angular, becoming convex; upper surface: brown, very dark with black undertone to mahogany, dull to glossy, epruinose, smooth to deeply fissured or warty; lower cortices: paraplectenchymatous, 30-50 µm thick; syncortex: 10-12 µm thick; eucortex, dark pigmented narrow upper layer, hyaline lower layer; algal layer: even and not interrupted; medulla: white, prosoplectenchymatous; lower surface: dark; attachment: broad, continuous with attaching hyphae, not truly stipe-forming, but attaching hyphae can be long and attenuated, from competition for probably light with areoles of D. oreina; Apothecia: one or two per areole, often lacking; disc: black, rough and uneven to almost gyrose with ridges, epruinose; parathecium: thin or poorly developed, but apparently expanding rarely to form blackened parathecial crown; epihymenium: dark brown, 10-15 µm thick; hymenium: hyaline, (60-)80-120 µm tall; paraphyses: 1.8-2 µm wide at mid-level, apically mostly expanded, 3-4 µm wide; subhymenium: 20-30 µm thick; hypothecium: indistinct; asci: cylindrical, 50-70 x 10-15 µm, 50-60-spored; ascospores: mostly globular, 3-6 µm wide, with distinct perispores; Pycnidia: not seen; Spot tests: UV-, all spot tests negative; Secondary metabolites: none detected.
Ecology and substrate: independent or emergent in thalli of Dimeleana oreina; World Distribution: North America (Nevada, New Mexico and Wyoming); Sonoran distribution: not yet known, but expected to occur as it is documented from NW and E of Arizona.
Notes (important - see taxonomic note above): Four specimens collected from Nevada and Wyoming by T. H. Nash were studied and a neotype selected from among them. The holotype was deposited in the Bouly de Lesdain in Dunkirk and was apparently lost during WW II. This description above differs from protologue in one important fact: specimens were not C+ red in cortex. The author thinks C+ spot test reaction in holotype was from chemistry derived from the host which was definitely C+ red according to Magnusson (1930). Acarospora succedens has not yet been found independent of D. oreina. While several other species have been observed growing out of thalli of other lichens (A. dispersa, A. interspersa, A. obnubila), they do not appear to be obligatory or host-specific juvenile parasites. Further specimens of A. succedens need examination to establish the degree of host-specificity. Its round spores with a perispore, low number per ascus, C- reaction, and well-developed syncortex are a distinct suite of characters for this western North America species. Several other species of Acarospora are common among thalli of D. oreina so caution is required in making a determination.
Relevant Literature: Knudsen, K. (2011) Acarospora nashii, a lichenicolous lichen from western North America. Bibliotheca Lichenologica106: 169-172.