Galapagos Species Database

Chemistry: Medulla 1) K+ yellow slowly turning orange, P+ deep orange: stictic gr.,6traces of norstictic acids (Andes & Galapagos); 2) K+ yellow turning red, P+ orange-yellow: salazinic, norstictic, 6 traces of connorstictic, 6traces of lobaric acids (Andes & Galapagos); 3) K+ yellow turning redorange, P+ deep yellow: norstictic, 6 traces of connorstictic acids (Andes only); 4) K and P2: unidentified tri-terpenoids UT2, rarely 6 traces of norstictic acid (Andes only).

U. rubicunda is characterized by terete branches, that are not constricted at the attachement point, numerous minute soralia, rarely enlarging or fusing, but always well-delimited, and a thick, hard and shiny cortex (in section), with a red-orange pigmentation, visible on the cortex surface when pronounced. The medulla is thin and compact, with an A/M ratio . 1.5, rarely smaller (1.25) (cortex 10.0–14.5%, medulla 13–20.5%, axis 35–49.5%, n 5 124). This species is very polymorphic in: thallus size (small erect to long, almost pendulous thalli); trunk pigmentation (concolor or rarely blackish); abundance of papillae and fibrils; soralia morphology; abundance of isidiomorphs; and intensity of red pigmentation. ‘‘Unpigmented’’ specimens of U. rubicunda are frequent, with a very faint pigmentation visible only as spots in longitudinal branch sections or close to the basal part only. Apart from the apparent lack of pigmentation, the main characteristics (terete branches bearing numerous minute soralia, thick and shiny cortex) still make it possible to identify these specimens. The presence of unidentified tri-terpenoids UT2 (chemotype 4), norstictic acid alone (chemotype 3) and lobaric acid (chemotype 2) in the medulla are newly reported here. Chemotypes 3 and 4 are rare chemotypes found exclusively in Andean specimens. Chemotype 2 (salazinic + norstictic acids) is the major chemotype in the Galapagos, whereas chemotype 1 (stictic acid) is the major chemotype in the Andes. Differentiation. For differences with Usnea rubricornuta and U. subrubicunda see under the description of these species. One specimen from the Galapagos Island exhibited a similar morphology and chemistry (chemotype 2), but with large soralia forming irregular schizidia-like patches on the terminal branches, without isidiomorphs. This particular type of soralia is observed in U. mirabilis Motyka, a species described from the Caribbean. Further studies from this area are needed to determine if U. mirabilis Motyka is a special morphotype of U. rubicunda. Usnea rubrotincta Stirt. from East Asia (Ohmura 2008) is a closely-related species with the presence of salazinic acid in the medulla. South American specimens with salazinic acid (chemotype 2) share the morphology of U. rubicunda specimens with stictic acid, and didn’t match with the morphological description of U. rubrotincta: terminal branches elongate and almost parallel, with soralia mostly plane and located on the fibrils. So far U. rubrotincta has not been found in South America.