Polysporangiate Anthers: Described for the First Time in Melastomataceae

Abstract

In taxonomic studies of the Melastomataceae anther morphology has been used along with fruit and seed characters to distinguish taxa mainly at a supraspecific level (among others De Candolle 1828a, b; Don 1832; Spach 1835; Grisebach 1864; Hooker 1867; Cogniaux 1883, 1891; Krasser 1893; Pereira 1961; Barroso et al. 1984). Characters used include the number and length of the stamens or anthers, position and form of the anther connective and the presence and type of indumentum on the stamens as well as the incidence of stamen dimorphism. Recent taxonomic revisions of genera of Melastomataceae and treatments of species of this family for local floras have shown that details of stamen morphology are important in the distinction of species or species groups, as may be observed in publications by Souza (1988), Baumgratz (1990), Renner (1989a, 1990, 1994), Martins (1989), Chiea (1990), Romero (1993), Wurdack et al. (1993), Baumgratz & Souza (1995) and Woodgyer & Nic Lughadha (1995). The anthers of the Melastomataceae are generally described as tetrasporangiate, dithecal, and bilocular at maturity. The single exception is Rhexia which although tetrasporangiate, is unithecal and becomes unilocular at anthesis through a breakdown of the septa. (Kral & Bostick 1969, Cronquist 1981, Renner 1993). During the preparation of the Melastomataceae account for the Flora of the Pico das Almas, in the state of Bahia, Brazil, (Baumgratz & Souza 1995) anthers of an apparently polysporangiate nature were encountered in two species of Chaetostoma , a phenomenon hitherto unknown in the Melastomataceae. The discovery gave rise to questions as to the importance of this character not only in the taxonomy of the tribe Microlicieae but also in the family as a whole. The taxonomy of the Microlicieae has long been recognised as problematic (Baillon 1880), and several of the genera within it are sorely in need of revision.