Thallus: fruticose, shrubby to subpendulous, up to 7(15) cm long branching: irregularly or dichotomously branched from a narrow holdfast branches: solid, lanceolate, plane or +canaliculate, up to 3(-5) mm wide surface: greenish gray to greenish yellow, irregularly uneven, shiny, without soredia pseudocyphellae: linear or ellipsoid, laminal or rarely marginal, flat to +depressed cortex: thin; chondroid strands: continuous, smooth, never forming bundles of hyphae Apothecia: common, submarginal, up to 1-3 mm in diam. disc: concave, with or without white pruina, without white margin; margin: entire; concolorous with the thallus, reticulately rugose, usually with dense pseudocyphellae asci: elongate-clavate, 8-spored ascospores: hyaline, 1-septate, broadly fusiform, slightly curved, 12-16 x 4.5-5 µm Pycnidia: not observed Spot tests: cortex K-, C-, KC+ yellow, P-; medulla K-, C-, KC-, P- Secondary metabolites: cortex with usnic acid (major); medulla with zeorin (±trace). Substrate and ecology: on bark World and Sonoran distribution: southern California, Baja California and Baja California Sur. Notes: Although Rundel and Bowler (1976) reported the absence of zeorin for R. leptocarpha, zeorin containing specimens were found in Mexico. Ramalina leptocarpha might be confused with R. celastri that differs in having flat laciniae, a convex apothecial disc without pruina, lacking pseudocyphellae on the margins and never producing zeorin. In addition, blades of R. leptocarpha produce apothecia on both sides, but they are usually characteristically found on upper side of blades in R. celastri. Ramalina leptocarpha resembles R. calicaris (L.) Fr., a European species, that differs in having +protruded pseudocyphellae and produces homosekikaic and sekikaic acid. Howe (1914) reported the occurrence of Ramalina fraxinea var. ampliata Ach., R. menziesii Tuck. and R. linearis (Sw.) Ach. from the Sonoran area. However, most specimens (in US) examined and annotated by him as these three species were found to be R. leptocarpha. The distribution of R. leptocarpha was plotted by Rundel and Bowler (1976).