Galapagos Species Database

Thallus erect-shrubby, to 8 cm long; ramifications anisotomic-dichotomous; trunk concolorous with the branches; branches tapering to slightly irregular; segments terete, not to slightly inflated; lateral branches not to slightly constricted at the attachement point; foveoles and maculae absent; papillae few to numerous on the main branches, hemispherical to verrucose, rarely eroding; fibrils usually short (to 3 mm) and thin, densely and irregularly covering the branches; soralia developing mainly on the cortex of terminal branches and at once enlarging to the branch diameter (fewer smaller soralia visible), plane to excavate, encircling the branch (cuff-like) and sometimes exposing the central axis; isidiomorphs few to abundant, remaining short within the soralia or growing into isidiofibrils, then typically mixing with fibrils on the branches; cortex 8.5–10%, thick and shiny (in section); medulla 21.5–27.5%, dense, with an orange, 6 continuous pigmentation just below the cortex; axis 27–39% (n 5 7); apothecia and pycnidia not seen. Chemistry: Medulla K+ yellow turning red, P+ yellow to orange: salazinic, galbinic, norstictic acids (n = 7).

Usnea grandisora is characterized by an orange subcortical pigmentation in the medulla, in combination with enlarging and excavate soralia. It has a thick and shiny cortex and parts of the branches are densely covered with isidiofibrils and fibrils. Differentiation. In the Galapagos, U. subdasaea and U. poliotrix share the orange subcortical pigmentation, but both have a thinner cortex and non-enlarging soralia. Otherwise U. subdasaea has a similar morphology, with numerous isidiofibrils and fibrils intermixed on the branches. In comparison with U. grandisora, U. subdasaea tends to have more irregular branches, being more constricted at the attachment point, a laxer medulla and a more typical cornuta-type CMA. In U. subdasaea soralia can rarely enlarge, but this usually results from the fusion of several smaller soralia. Soralia of all size can be observed on the branches of U. subdasaea, the majority remaining small, whereas in U. grandisora large soralia are in the majority. The cortex thickness remains the best diagnostic character to distinguish these two species. In tropical Africa, Usnea bicolorata Motyka also has enlarging soralia and a subcortical pigmentation, but differs in the regular branches, the black base, the rarity of isidiomorphs and a different chemistry (Swiscow and Krog 1979, Ohmura et al. 2010). Since the type of U. bicolorata has been lost, Swinscow & Krog (1979) based their description on the type of U. bicolorata var. pseudorubescens (holotype G!), which doesn’t correspond to U. grandisora. In Australia, Stevens (1999) described U. bicolorata var. australiensis based on a new chemotype (salazinic, galbinic, norstictic acids). She described this taxon with a concolorous or black base and numerous isidiomorphs from pseudocyphellae (non-enlarging soralia), which doesn’t correspond to U. grandisora. Further studies on Australian specimens are needed to clarify their status.