syn. Rinodina adirondackii H. Magn., Bot. Not. 1947: 48.
Type. U.S.A. NEW YORK. [Essex Co.], Adirondack Mountains, Chapel Pond, near St. Huberts, 1600ft, on cedar in gully, 1933, J.L. Lowe 3751 (UPS ‑ holotype!, isotype NY).
Description. Thallus thin, light grey, continuous, becoming rimose; surface plane to rugose, shining or sometimes matt; margin indeterminate; prothallus lacking; vegetative propagules absent. Apothecia often erumpent, becoming broadly attached, frequent, rarely contiguous, to 0.40-0.80 mm diam.; disc black, persistently plane to slightly convex; thalline margin concolourous with thallus, 0.05‑0.10 mm wide, entire and persistent; excipular ring often present, raised or confluent. Apothecial Anatomy. Thalline exciple 35‑80µ wide laterally; cortex poorly developed, structure partially occluded by crystals, 5‑10 µm wide; epinecral layer sometimes present, 5‑10 µm deep; crystals present in cortex and medulla; cortical cells to 4.5-5.0 µm wide, not pigmented; algal cells to 8.5‑15.5 µm long; proper exciple 15‑25 µm wide, usually lightly pigmented, expanding to 25‑50 µm wide above; hypothecium hyaline, 35‑80 µm deep; hymenium 110‑140 µm high, not inspersed; paraphyses ca. 2.0 µm wide, conglutinate, apices expanded to 3.0‑5.0 µm wide, lightly pigmented and immersed in dispersed pigment forming a red‑brown epihymenium; asci 75‑100 x 25‑34 µm. Ascospores 8/ascus, Type A development, Pachysporaria‑type I, (21.5-)28.0‑30.0(-36.5) x (9.0-)14.0‑16.0(20.5) µm, average l/b ratio 1.8-2.1, lumina irregularly angular (almost polygonal) at first, becoming Physcia- or Mischoblastia-like, then rounded, apical walls remaining thick; torus becoming prominent; walls not ornamented. Pycnidia immersed in thallus, ostioles hardly pigmented; conidiophores type I; conidia bacilliform, 3.5-5.5 x ca. 1.0 µm.
Chemistry. Spot tests, K‑, C‑, KC-, P+ cinnabar (with red crystals); secondary metabolites, pannarin in medulla and cortex.
Substrate and Ecology. Corticolous, collected mostly on Thuja occidentalis, also on Tsuga canadensis in moist habitats and on Carya and Magnolia in the southernmost part of its range above 600 m.
Distribution.Rinodina adirondackii was previously considered a North American endemic, rather rare in the Great Lakes-Appalachian region. According to Sheard (2018, Herzogia31(1)Teil 2, p. 408 & 418), the taxon must be considered a synonym of Rinodina tenuis, previously thought to be endemic to Japan, but now known to also occur in northeastern Russia in addition to North America.
Notes. This species is well characterized by its light grey, thin, more or less continuous thallus, the presence of pannarin and very large, Pachysporaria-type I spores. The spores are rather variable in both size and structure. The latter variation is mostly due to the developmental sequence in which the lumina are at first irregularly angular (almost polygonal), becoming Physcia- or Mischoblastia-like and finally rounded. At the irregularly angular stage they are similar to the immature spores of R. verruciformis, and when mature with well developed tori they are comparable to R. perreagens and R. sheardii. An epinecral layer often gives the thallus surface a shining appearance and a superficial similarity to R. ascociscana as noted by Magnusson. The larger, Physcia‑type spores and lack of secondary products in R. ascociscana indicate that there is no close relationship. Forms of R. tenuis with erumpent apothecia and light grey thalli may give the impression of R. subminuta with large apothecia, a similarity which is reinforced by the fact that the discs are frequently eroded by invertebrates. The smaller, Physcia-type spores and lack of pannarin in the latter easily separate the two species. Rinodina willeyii is a closely related sorediate species, the similarities being discussed under that species.
Specimens examined. CANADA. ONTARIO. Nipissing District, Lake Timagimi, R.F. Cain 26635 (COLO, WIS). QUEBEC. Lac Claire, 1888 (FH). U.S.A. ILLINOIS. Fulton Co., Canton, 1880, J. Wolf (PH). MAINE. Hancock Co., Jordan Pond, Acadia Nat. Park, T.J. Sullivan 3546 (MIN). MASSACHUSETTS. Bristol Co., New Bedford, 1884, H. Willey (US); H. Willey 761 (FH). MICHIGAN. Baraga Co., Sidnaw, R.C. Harris 8096; Gogebic Co., Great Conglomerate Falls, H.A. Imshaug 20702 (both MSC). MINNESOTA. Auburndale, 1902, B. Fink (MIN); St. Louis Co., Babbitt, C.M. Wetmore 28052 (MIN). NEW YORK. Essex Co., Chapel Pond, J.L. Lowe 3751 (UPS holotype). NORTH CAROLINA. Jackson Co., Highlands, T. Tønsberg 21838 (BG). WISCONSIN. Forest Co., Popple River, J.A. Jesberger 459 (SASK).