Abstract

COTA-SANCHEZ, J. Hugo  and  BOMFIM-PATRICIO, Márcia C.. Seed morphology, polyploidy and the evolutionary history of the epiphytic cactus Rhipsalis baccifera (Cactaceae). Polibotánica [online]. 2010, n.29, pp.107-129. ISSN 1405-2768.

A SEM survey of seed, stem, stomata, and fruit characters was conducted to investigate patterns of infraspecific variability in Rhipsalis baccifera. New and Old World seeds were analyzed to assess the taxonomic value of their morphological features and the presence of gigas characters in polyploid versus diploid subspecies. The seeds are mussel-shaped and correspond to the Rhipsalis-type. Old World representatives have primarily oval seeds, whereas narrowly oval to oval seeds are more common in New World accessions. The seed coat is glossy, smooth, and without secondary sculpturing. The cell outline is slightly irregular with an overall elongate to rectangular shape. Cell size increases from the hilum-micropylar region to the apical portion of the seed. Seed and cell size increase with increasing level of polyploidization, its maximum expression occurring in polyploid African populations. It is likely that increase in seed size in the Old World is correlated with polyploid cytotypes. An increase in stomatal cell size is not evident with an increase in chromosome number, though stem and fruit size and the number of stomata are higher in the Old World polyploid subsp. horrida. The existence of smaller seeds in Paraguay and northern Argentina suggests that this South American region is the center of origin of R. baccifera, from where it radiated to North America and the Old World via eastern Brazil. We hypothesize that the extensive geographic distribution of R. baccifera in the New and Old Worlds has been possible due to reproductive strategies, progressive and recurrent cycles of polyploidy and dispersal events by migratory birds.

Keywords : Cactaceae; gigas characters; polyploidy; Rhipsalis-type seed; Rhipsalis baccifera; seed morphology; SEM; stomata.

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