Bromus catharticus in South America (Poaceae: Bromeae) Paul M. PetersonDepartment of Botany NHB-166, National Museum of Natural History, Smithsonian Institution, Washington, D.C. 20560, U.S.A. Ana Maria Planchuelo CONICET: Facultad de Ciencias Agropecuarias, Universidad Nacional C6rdoba, Casilla de Correo 509, 5000 C6rdoba, ArgentinaABSTRACT. A new combination, Bromus catharti-cus var. rupestris, is made. Based on morphologicalevidence this taxon seems best recognized at thevarietal level. Detailed illustrations of B. catharti-cus var. rupestris and B. catharticus var. catharticusare included along with morphological descriptions,distributions, and representative specimens.RESUMEN. Se realiza una nueva combinaci6n,Bromus catharticus var. rupestris. Sobre la base delas evidencias morfol6gicas, parece mejor recono-cer este taxon a nivel de variedad. Se incluyen il-lustraciones detalladas de B. catharticus var. rupes-tris y B. catharticus var. catharticus junto condescripciones morfol6gicas, distribuciones y espe-cimenes representativos. Bromus L. comprises approximately 150 speciesfound mainly in the temperate regions of bothhemispheres (Clayton & Renvoize, 1986). The ge-nus has been divided into five to seven groups(Stebbins, 1981; Tsvelev, 1976), depending uponthe recognition of Anisantha C. Koch, BoissieraSteudel, Bromopsis Fourreau, Ceratochloa P. Beau-vois, and Nevskiella Krecz & Vvedensky as sepa-rate genera. In a recent treatment of Bromus in theUnited States and Canada, Pavlick (1995) recog-nized five sections: Bromopsis, Bromus, Cerato-chloa, Genea, and Neobromus. In North and South America, Bromus sect. Cer-atochloa consists of approximately 18 species ofwhich B. catharticus Vahl is a member (Matthei,1986; Nicora, 1978; Pavlick, 1995; Pillay & Hilu,1995; Soderstrom & Beaman, 1968; Tovar, 1993;Zuloaga et al., 1994). This section is entirely nativeto the New World and contains an extensive poly-ploid complex, base of x = 7. All taxa thus farexamined are either hexaploid (2n = 42), octoploid(2n = 56), or duodecaploid (2n = 84) (Armstrong,1991; Pavlick, 1995; Stebbins, 1956, 1981; Steb-bins & Tobgy, 1944). Bromus catharticus and im-mediate relatives are all hexaploid (Naranjo, 1992). The Bromus catharticus complex presently con-tains six taxa (Planchuelo, 1991; this paper): B. bonariensis Parodi & J. A. Camara, B. brevis Nees ex Steudel subsp. brevis, B. brevis subsp. festuca-rioides Covas & Millot, B. catharticus, B. parodii Covas & Itria, and B. striatus Hitchcock [= B. ca-tharticus var. striatus (Hitchcock) Pinto]. We choose to recognize B. catharticus, as proposed by Pinto-Escobar (1976), as the true name for rescue grass, rather than that proposed earlier by Raven (1960) as B. willdenowii Kunth. The Andean species, B. unioloides Kunth, and B. willdenowii are treated here as taxonomic synoyms of the older, B. cathar-ticus. Studies of the Bromus catharticus complex (ex-cluding B. striatus) indicate that the crossabilityamong four species (B. bonariensis, B. brevis, B.catharticus, B. parodii) is low (Naranjo, 1992). Inrecent years the use of hybridization studies in sys-tematics has declined since exceptions to the cor-relation between pairing and genome homologyhave been found (Seberg, 1989; Doyle et al., 1990a,1990b). Several authors (Ragonese & Marco, 1941,1943; Perez L6pez, 1975; Cladera, 1979; Pahlen etal., 1980; Wolff et al., 1996) described the mor-phological features of B. catharticus under varyingenvironmental conditions. More recently, Abbott etal. (1996), Aulfcino and Arguri (1996), and Gu-tierrez et al. (1996) pointed out phenotypic varia-tion in the vegetative features of B. catharticus. Thepolymorphic nature of B. catharticus has led to thedescription of numerous taxa at the specific andvarietal levels, and we offer our treatment here. Pri-or results (Planchuelo, 1991) of a phenetic analysisof 16 morphological characters suggest that B. bon-ariensis, B. brevis, and B. catharticus be consideredconspecific. At the present time we choose to recognize B.bonariensis, an endemic of Provincia Buenos Aires,Argentina, as a separate species since there ap-pears to be no overlap with other taxa in the com-NovoN 8: 53-60. 1998.