The genus Pseudoparmelia Lynge has its center of diversity in tropical South America (Brazil), with a secondary center in southern Africa. The genus is characterized by a pale to olive-brown lower surface with simple rhizines, isolichenan in the cell walls, a pored epicortex, a pale-yellow or yellow medulla, and secalonic acids and low concentrations of atranorin in the upper cortex. Pseudoparmelia has secondary-product chemistry characterized by secalonic acid derivatives together with p-orcinol meta-depsides or pf-orcinol depsidones. A total of 22 known compounds is reported for the genus, based upon thin-layer and high-performance liquid chromatographic analyses of273 specimens. Pseudoparmelia is now considered to comprise 16 species seven of which are here described as new. Four new combinations within the genus are made. The generic concepts in the macrolichen family Parmeliaceae have undergone enormous changes over the last 20 years (Elix 1993; Hale 1984; Kirnefelt et al. 1992, 1993), and although various changes were not well accepted initially, the situation has improved in recent time. One of the currently accepted segregates is Pseudoparmelia Lynge, a genus first erected early this century (Lynge 1914). Although Santesson (1942) subsequently pointed out that the 'pseudocyphellae' that Lynge considered particularly characteristic of his new genus were artifacts caused by tearing of rhizines from the lower surface, the delimitation of the genus was redefined by Hale (Hale 1974, 1976a), and considered to include a total of 76 species with a cosmopolitan distribution. Subsequently it became obvious that Pseudoparmelia so defined (Hale 1974, 1976a) was a polyphyletic assemblage of species, and a new circumscription of Pseudoparmelia s. str. (Hale, 1986) excluded the majority of species formerly placed in this genus. In fact only four species remained, namely P. chapadensis, P. cyphellata, P. hypomiltha, and P. sphaerospora. Hale (1986) and Elix (1993) considered that the following characters were most significant in distinguishing this genus: small ellipsoid to subspherical ascospores (5-12 X 4-8 pCm), bifusiform to elongate bifusiform conidia, yellow-pigmented upper cortex and medulla due to a high concentration of secalonic acid(s), pale lower surface with simple rhizines, negative test for lichenan in the fungal cell walls, p-orcinol depsidones in the medulla, and traces of atranorin in the cortex. Here these characters have been re-evaluated. Although we are substantially in agreement with the importance of these characters, we have found a greater range of variation of several features (e.g., the shape and size of the conidia and the ascospores) than previously reported. Upon undertaking our present study we soon realized that the morphological and chemical variation within the genus was more extensive than had previously been appreciated, and we now consider that a number of new species should be recognized. MATERIALS AND METHODS This study is based primarily upon collections in ASU, B, NY, US, and in the herbarium of K. Kalb, the herbaria with the best representation of materials from the parts of South America in which Pseudoparmelia is most abundant. Other specimens were borrowed from B, BM, CANB, FH, G, H, M, PRE, S, and w. In all, 273 herbarium specimens were studied, all of which were analyzed by thin-layer chromatography (TLC) and by high-performance liquid chromatography (HPLC). For each species we cite at least one specimen from every major political subdivision from which material was seen. All the major phenolic metabolites encountered were readily identified by the TLC methods described elsewhere (Elix et al. 1986, 1988; Elix & Ernst-Russell 1993). In addition, a number of specimens contained traces of unknown compounds related to secalonic acid A, for which critical controls were not available. A detailed chemical study of these compounds would exceed the scope of the present research, consequently these compounds are simply recorded as 'unknown' secalonic acid derivatives.