The Taxonomy of Helenium sect. Cephalophora (Asteraceae)

Abstract

A systematic treatment is presented for the 8 presently recognized taxa of sect. Cephalophora, with synonymies, typifications, descriptions, discussions, and range maps. Helenium ovallense is described as new, H. vallenariense is officially transferred to Helenium from Cephalophora, and H. leguiffei is reduced in status to a variety of H. urmenetae. Chromosome counts are reported for 7 of the 8 taxa; all were diploid with n = 17. Helenium sect. Cephalophora comprises a group of closely related taxa that are confined to Chile (H. aromaticum has been collected in southern Peru, where it was apparently introduced but does not appear to persist). This taxon has been separated from the interior Argentinian section of Helenium by the Andean range for a very long period of time. As a result, considerable morphological differentiation between the two groups has occurred. Nevertheless, they are phylogenetically quite closely related and consequently are treated as but separate sections of Helenium. Treatment of the Argentinian taxa is being prepared for separate publication. Section Cephalophora was originally treated as a separate genus, Cephalophora, described by Cavanillas (1801). Hoffmann (1894) submerged Cephalophora in Helenium as a separate section. The section subsequently has received very little taxonomic attention, having last been treated by Reiche (1903) in his Flora de Chile. The taxonomic treatment presented here is the result of morphological, field, cytological and flavonoid chemical studies. In addition to the examination of herbarium specimens, 71 populations were collected by the author on two separate field trips. All 71 populations were examined for flavonoid constituents and 57 were examined for chromosome number (Appendix). For cytological studies, bud material was fixed and stored in a modified Carnoy's solution: chloroform, absolute ethanol and glacial acetic acid (4:3:1). The chromosomes were stained with aceto-carmine and counts were obtained from microsporocytes at diakinesis, metaphase I or anaphase I for seven of the eight taxa, Helenium insulare being the only species that was not encountered during the field trips. All populations examined exhibited a chromosome number of n = 17, confirming the only previously reported count for this section of 2n = 34 for H. aromaticum (Bolkovshikh et al., 1969). The consistency of chromosome number in sect. Cephalophora is somewhat surprising in view of the extensive aneuploidy found in the North American species of Helenium (Grashoff ' Botany, University of Tennessee, Knoxville, TN 37916.