Chromosome Numbers of Madagascar Plants

Abstract

Chromosome numbers are reported for 19 species in eight families of flowering plants of Madagascar. Included are first reports for 14 species. First counts for the genera Kaliphora (n = 16) and Haronga (n = 10) also are presented. A new low number (n = 7) is reported for the genus Vernonia, and the possible allopolyploid origin of New World taxa of the genus based on x = 17 is discussed. Although the flora of Madagascar contains many interesting and poorly known genera and families, chromosome counts are available for relatively few species. The present paper inaugurates what is intended to be a sustained effort to record the chromosome numbers of Madagascar plants so they will be available to assist in interpretation of phytogeographic and evolutionary relationships. MATERIALS AND METHODS With two exceptions, chromosome numbers reported here were determined from microsporocytes undergoing meiotic divisions. The two counts in the genus Aloe were made from microcytes undergoing the first mitotic division of microgametogenesis. All floral bud materials used for chromosomal determinations were preserved in a modified Carnoy's fixative (6 chloroform: 3 absolute ethanol: 1 glacial acetic acid). These were stored in the fixative under refrigeration until they were transported to the University of Hawaii where acetocarmine slide preparations were made according to a modification of Beeks' method (Beeks, 1955). Observations were made with a Zeiss Photoscope III equipped with phase contrast optics. Voucher specimens of all cytological determinations have been deposited in the Herbarium of the Service de Botanique, Universite de Madagascar, Tananarive (TAN).