Trans. Connecticut Acad. Arts 38: 297 (1952).
Protolog: Data lacking.
Type locality: USA, Florida, Seminole Co., Sanford, 1924, S. Rapp in Sandstede, Cladon. Exs. 1398 p.p. (US - holotype; UPS - isotype).
Barcode: Data lacking.
Coordinates: Data lacking.
Thallus: Primary thallus mostly persistent, consisting of 2-4 mm long and 2 mm wide, elongate, sparsely lobed, often incurved squamules. Podetia slender to rather robust, 3-6 cm tall, 0.5-1.5 mm thick, usually of determinate growth, pale grey to dark brownish, usually strongly melanotic at the base, sparsely branched, composed of centrally proliferating scyphi in 3-12 tiers; scyphi 3-14 mm long, the basal one sometimes longer, up to 25 mm, abruptly flaring, shallow, 2-4 mm wide, not perforated or with some slits in old podetia; scyphal margins upturned, soon denticulate to slightly divided, much dissected when abundantly fertile. Podetial surface areolate-corticate, sometimes squamulose or scaling off to expose the stereome, minutely pruinose-arachnoid, especially in young parts. Podetial wall 300-340 µm thick; cortex 24-28 µm; medulla 140-200 µm; stereome 100-140 µm, distinctly delimited, soon darkening and finally blackening, rather soft; surface of the central canal papillose. Conidiomata 0.2-0.25 x 0.2-0.25 mm, sessile to short-stalked, on scyphal margins, occasionally on the bottom of the scyphi, globose to shortly pyriform, constricted or not at base, containing hyaline slime. Hymenial discs 1-1.5(-3) mm wide, on short, flat stalks on the margins of the scyphi, long remaining flat on top but finally convex, dark to pale brown (Ahti & Sipman 2013: 80).
Photobiont: Data lacking.
Chemistry: There are three chemical races:
Race I: Fumarprotocetraric acid and traces of protocetraric, quaesitic acid (subconstant), confumarprotocetraric acid, and other unknown minor components (Ahti 2000). Colour reactions: P+ orange red, K-, KC- (Ahti & Sipman 2013: 80).
Race II: with psoromic acid instead of fumarprotocetraric acid (with colour reaction P+ yellow).
Race III: with additional atranorin (colour reaction K+ pale yellow) (Ahti & Sipman 2013: 80).
Ecology: In the Neotropics it is a high-altitude species, common along the Andes and in SE Brazil, and sporadically found around 2000 m alt (Ahti & Sipman 2013: 80).
Molecular data: Genbank
Distribution: A widespread species occurring in N America, Asia, Africa and Melanesia. Database
Note: There is a variety:
Cladonia rappii var. exilior (Abbayes) Ahti, Ann. Bot. Fenn. 20: 5 (1983). Basionym: Cladonia calycantha var. exilior Abbayes, Bryologist 52: 94 (1949) Panama, Chiriquí, Chiriquí volcano, 1941, P. F. Scholander s.n. (US - lectotype; REN-Abbayes - isolectotype). Lectotypified by Ahti (1993: 92).
Cladonia rappii is rather variable so that further studies may reveal that it contains more than one taxon. One specimen from Venezuelan Guayana (Huber 10046) is particularly deviating by its numerous short (3-4 mm) internodes.
From elsewhere known are chemical strains with psoromic acid instead of fumarprotocetraric acid (with colour reaction P+ yellow), and with additional atranorin (colour reaction K+ pale yellow).