STUDIES IN MEXICAN ARCHIBACCHARIS (COMPOSITAE) Guy L. Nesom Departaent of Botany, University of Texas. Austin 78713 ABSTRACT The taxa of Archibaccharis hieraciifolia , as treated by Jackson (1975) are recognized as A^ hieracioides (S. F. Blake) S. F. BlcJce and A. auriculata (Hemsley) Nesom. Each of Jackson's four varieties of Ai hirtella (DC. ) Heering is treated as a separate species: A. hirtella . A. intermedia (S. F. Biake) B. Turner, A. albescens (J. D. Jackson) Nesom, and A. taeniotricha (S. F. Biake) Nesom. Archibaccharis asperifolia (Benth.) S. F. Blake is veiewed as a variable species that includes Aj_ sescenticeps (S. F. Biake) S. F. Blake. A new species of sect. Hirtella from Veracruz is described: A. veracruzana Nesom. Archibaccharis was recently revised by Jackson (1975), but even since his incisive study many new collections have been made, allowing a better understanding of species limits and variabitility. One new species has been described from Costa Rica (Sundberg 1984), and Turner (1984) has presented observations resulting from his study of the genus in Veracruz. During my study of the Mexican taxa of Archibaccharis . another new species has come to light, and several new combinations and changes in rank are required. I . The Archibaccharis hieracioides group The nomenclature of Archibaccharis hieraciifolia Heering sensu lato (and sensu Jackson) has been discussed by Biake (1927), McVaugh (1972, 1984) and Jackson (1975). Jackson treated the group as represented by three varieties, but McVaugh (1984) could not distinguish between vars. glandulosa and hieraciifolia of Jackson, nor can I. Thus, I recognize only two taxa, though the nomenclature is arranged differently, since each is treated as a separate species. McVaugh also was the first to recognize that an earlier name at the species rank is available for Archibaccharis hieraciifolia Heering (Pi uchea auriculata Hemsley). Archibaccharis auriculata and A^ hieracioides appear to be closely related and are easy to recognize because of the glands on both their stems and leaves. Although the two have sympatric distributions over a large range, each maintains its unique features and behaves as a distinct species. Some plants may show intermediacy, perhaps due to hybridization, but certainly not to the degree expected if they were conspecific. Archibaccharis campii S. F. Biake is retained here until more material can be examined, but it is very similar to A^ hieracioides and perhaps conspecific with it. 122



Studies in Mexican Archibaccharis (Compositae)

G L Nesom
Phytologia 65: 122-128 (1988)

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