Type. [U.S.A.] FLORIDA. Sanford, 1909, on trees, s.d. S. Rapp s.n. (U ‑ holotype!).
Description.Thallus thin, light grey, continuous becoming rimose, sometimes rimose-areolate; areoles to 0.40-0.70 mm wide; surface plane becoming rugose, matt; margin determinate; prothallus often present, limiting, entire or somewhat fimbriate, dark; vegetative propagules absent. Apothecia broadly attached or slightly narrowly attached, frequent, dispersed at first, sometimes becoming contiguous and angular by compression, to (0.60-)0.80‑1.40 mm in diam.; disc dark brown to black, often lightly pruinose, particularly when young, more obvious when moist, plane, eventually becoming slightly convex; margin entire, sometimes becoming rugose, 0.05‑0.10 mm wide, persistent; excipular ring absent. ApothecialAnatomy. Thalline exciple 50-90 µm wide laterally; cortex poorly delimited; epinecral layer sometimes present, ca. 10 µm wide; crystals in cortex and medulla; algal cells to 7.5‑14.0 µm long; thalline exciple 80-115 µm wide below; cortex 10-30(-50) µm wide, structure intricate; proper exciple 5‑15 µm laterally, expanding to 10‑25 µm above; hypothecium (50‑)75‑110 µm deep, usually slightly inspersed, developing medial stipe, sometimes yellowish; hymenium 70‑95 µm high, not inspersed; paraphyses 1.5‑2.0 µm wide, conglutinate, apices to 3.0‑4.5 µm wide, lightly capitate, immersed in light pigment forming a light orange- or red-brown epihymenium, with crystals; asci 40‑70 x 14‑20 µm Ascospores 8/ascus, Type A development, Dirinaria‑type, (13.0-)16.5-17.5 (-21.0) x (6.0-)8.0‑8.5(-10.0) µm, average l/b ratio 2.0-2.2, sometimes slightly swollen at septum, more so with KOH, lumina Physcia-like at first, becoming less angular; torus not present but pigmentation developing in the septal region of mature spores may be mistaken for a torus; walls ornamented at maturity. Pycnidia ostioles brownish, emergent; conidiophores type V; conidia bacilliform, 3.5-4.5 x ca. 1.0 µm.
Chemistry. Spot tests, K+ yellow, C‑, KC-, P‑ or P+ yellow, rarely P+ cinnabar, epihymenium with P+ red needles; secondary metabolites, atranorin and zeorin in thallus (confirmed by T. Tønsberg), pannarin in epihymenium.
Substrate and Ecology. Corticolous, collected on Acer rubrum, Carya and Salix but these substrates may not be representative due to the large proportion of old records for which substrate is not recorded.
Distribution. A relatively infrequent North American endemic, R. granuligera has a southeastern distribution with outliers on the northeast coast. It might also be considered to be a Coastal Plain species with a higher proportion of inland records than the more typical R. maculans. The relatively large number of pre-1960 records suggests that the present distribution of this species is restricted to a portion of its former range.
Notes. The name R. granuligera was given by Magnusson to draw attention to the crystalline inclusions of the medulla which obscure the algal cells and structure of the cortex. These crystals appear to be due to the presence of atranorin in both the cortex and medulla which can be observed to dissolve on application of KOH. The species is further characterized by the presence of pannarin crystals in the epihymenium and in this regard it is similar to R. marysvillensis of the west coast. This last species is best separated from R. granuligera by lack of medullary crystals and by its larger, broadly ellipsoid spores. The thallus morphology of R. granuligera may possibly cause confusion with the largely sympatric R. maculans but the thallus of this species is never light grey, does not contain atranorin and its spores belong to Pachysporaria-type II.
The spore lumina of R. granuligera are angular and Physcia-like but mature spores are often swollen at the septum, and become more so in KOH. They have therefore been classified as belonging to the Dirinaria-type despite the absence of Type B development which is typical of this spore type. The spores are rather variable in size having a CV > 10%.
Specimens examined. CANADA. NEW BRUNSWICK. Charlotte Co., Campobello Island, 1902 (FH). U.S.A. ALABAMA. Conecuh Co., Brooklyn, Beaumont; Lawrence Co., Moulton, 1871, T.M. Peters (both FH); Tuscaloosa Co., 10 mi S Tuscaloosa, F.T. McFarland 596 (WIS). FLORIDA. Seminole Co., Sanford, 1909, S. Rapp (UPS). GEORGIA. Chatham Co., Savannah, A.B. Hervey (FH); Jasper Co., Ocmulgee Flats, S.Q. Beeching 130, 191 (PH). LOUISIANA. Bayou Tastue, 1893, A.B. Langlois; Bois Charnant, 1893, A.B. Langlois; Duchamps, 1894, A.B. Langlois (all US); Bossier Par., Lake Bisteneau, S.C. Tucker 11454 (SASK); East Feliciana Par., 5.6 mi SE Clinton, S.C. Tucker 18547 (MSC); Lafourche Par., W Thibodaux, S.C. Tucker 21315 (CANL); Sabine Par., Toledo Ben Reservoir, S.C. Tucker 8973 (MSC); St. Helena Par., 5 mi NNE Chipola, S.C. Tucker 11101a (LSU); St. Landry Par., Grand Coteau, 1894, A.B. Langlois; Terre Bonne Par., Bayou Savoie, 1889, A.B. Langlois. MASSACHUSETTS. Bristol Co., Dartmouth, 1882, H. Willey (all US); New Bedford, Willey 72a (FH). MISSISSIPPI. Amite Co., Gloster, S.C. Tucker 30632 (SBBG). NORTH CAROLINA. Wake Co., William B. Umstead State Park, J.C. Lendemer 8319 (PH). TENNESSEE. Polk Co., Hiwassee River, A.C. Skorepa 5990 (BALT). TEXAS. Brazos Co., Bryan, 1919, N.L. Nelson (US).