Matías Morales

Chromosome and morphological studies in the Mimosa debilis complex (Mimosoideae, Leguminosae) from southern South America

Mimosa debilis Humb. & Bonpl. ex Willd. and M. nuda Benth. were grouped in specific and infraspecific complexes. Both taxa showed exomorphological similarities, with conflicts in their taxonomic circumscription and present different ploidy levels. The objective of the present contribution was to analyse chromosome numbers of different populations and to evaluate morphological characters of specimens from Paraguay, Argentina and boundary regions. Chromosome numbers of M. debilis var. debilis (2n = 2x = 26 and 2n = 4x = 52) confirmed previous reports, whereas those of M. nuda var. glaberrima (2x = 26, 4x = 52), M. nuda var. gracilipes (2x = 26, 4x = 52) and M. nuda var. nuda (4x = 52) are presented for the first time. Variation was observed in habit, foliar and floral morphology and was correlated with the chromosome number and the geographical distribution of the taxa. Groups with stable morphological characters and restricted geographic distribution were identified. Also, the results showed a pattern of hybrid swarms and polyploids of different origin that may explain the existence of taxonomic conflicts in the M. debilis–M. nuda species complex. On the basis of these results, M. nuda should be included in the synonymy of M. debilis.

Morphometric and Cytogenetic Studies in Mimosa diversipila (Mimosoideae, Leguminosae) and Their Taxonomic and Evolutionary Inferences

Abstract Here we describe the morphological variability, chromosome number, and chromosome size in Mimosa diversipila. This species comprises two varieties, which are distinguished by the indumentum. However, this character is insufficient for circumscription of these infraspecific taxa. Using multivariate techniques, we found that quantitative characters were useful for identification of the varieties, which also have a different geographic distribution. Cytogenetic studies revealed that these taxa form a polyploid complex and that the polyploidy may contribute to the morphological variability observed.

A New Polyploid Species of Mimosa (Leguminosae, Mimosoideae) from the Highlands of Southern Brazil

Abstract Mimosa tucumensis (Leguminosae), a new species from M. sect. Mimosa ser. Mimosa subser. Mimosa is described and illustrated. This taxon is found in southern Brazil (Paraná State), in “campos de altitude,” an environment different from the typical habitat of other entities in this subseries. Mimosa tucumensis is morphologically close to M. debilis, M. velloziana, and M. sensibilis, but differs from these principally by the presence of humifuse stems with adventitious roots, considerably longer petioles and peduncles, and foliar venation. In addition, cytological characterization of this new taxon is provided and discussed in relation to the nearest species. This taxon appears to be narrowly restricted to grasslands on a handful of closely adjacent peaks in the Paraná State adding to the notable endemism of this area. On the basis of morphological, cytological, and geographical data, some evolutionary considerations are inferred.