María de las Mercedes Sosa

Karyotype analysis of the southernmost South American species of Stemodia (Scrophulariaceae)

Abstract The aim of the present study was to examine the somatic chromosomes of seven species of Stemodia (Scrophulariaceae). The karyotypes of Stemodia ericifolia (2n = 22 = 20m + 2 sm), S. hassleriana (2n = 22 = 20m + 2sm), S. hyptoides (2n = 22 = 20m + 2sm), S. hyptoides (2n = 44 = 40m + 4sm), S. lobelioides (2n = 44 = 40m + 4sm) and S. stricta (2n = 22 = 20m + 2sm) were analyzed for the first time. All the species studied showed a predominance of metacentric chromosomes and a lower proportion of submetacentric pairs. The chromosomes in all the species were found to be small with a mean chromosome length of 1.42 μm, varying from 0.77 μm in S. hyptoides (2n = 66) to 2.10 μm in S. lanceolata. The differences in the asymmetry of the karyotypes were small, for which it is possible to assume that the great diversification of the genus has been accompanied by very small changes in the structure of the chromosomes.

Pollen morphology of eight species of Stemodia (Plantaginaceae) from South America

The pollen morphology of eight species of Stemodia L. (Plantaginaceae) was analysed with the aim of refining the taxonomy of this genus. The pollen grains were examined with both light and scanning electron microscopes. The pollen grains are spheroidal, sometimes prolate-spheroidal, small, with a subcircular or subtriangular amb, 3- or 4-colporate and with a long colpus that reaches the poles, defining a small, circular to slightly lalongate apocolpium with irregular margins. The exine is tectate, foveolate or microperforate, 1 µm thick and uniform. The species of Stemodia analysed here exhibit morphological homogeneity, which suggests that the genus is stenopalynous.

Cytogeographic Analysis of Southern South American Species of Stemodia (Scrophulariaceae)

Chromosome numbers for 52 populations representing eight South American species of Stemodia (Scrophulariaceae) were determined. The numbers 2n = 22 found in S. hassleriana and S. palustris, and 2n = 44 in S. lobelioides are the first records for the species, while those found in S. hyptoides (2n = 22, 44) and S. stricta (2n = 22) constitute new cytotypes for those species. The basic chromosome number X = 11 was confirmed for the New World species. Chromosome numbers indicate the existence of a polyploid series in S. hyptoides with 2n = 22, 44, 66. Moreover, the existence of at least three different ploidy levels, both within and among species, indicates that polyploidy has been one of the mechanisms involved in the evolution of the genus. The geographical distribution of different species and cytotypes are analysed and discussed in the light of their extant morphological variation and taxonomic implications.

Systematic significance of cypsela morphology in Lessingianthus (Vernonieae, Asteraceae)

Abstract. The taxonomic significance of cypsela features of South American species of Lessingianthus (Vernonieae, Asteraceae) is analysed for the first time and discussed in relation to other genera of the tribe Vernonieae. The morphology of the cypselae of 112 species of the genus were analysed using stereo-, light and scanning electron microscopy (SEM) to evaluate the infrageneric relationships and their reliability as taxonomic markers at a generic level. Characters such as cypsela pubescence, carpopodium structure, crystals and idioblasts on the fruit wall were examined. We established three types of cypsela on the basis of the presence or absence, and type of trichomes. Carpopodium is present in all species of the genus. Crystals are very variable in shape and size, with prismatic (rectangular and hexagonal) and styloid shapes. Idioblasts are present in all of the species, except for two. Cypsela features of Lessingianthus are often widespread in other related genera of Vernonieae. Therefore, these characters are not good taxonomic markers at the genus level, but they are valuable within genera to differentiate related species from one another.

Chromosome numbers and DNA content in some species of Mecardonia (Gratiolae, Plantaginaceae)

Abstract Cytogenetic characterization and determination of DNA content by flow cytometry of five species of Mecardonia Ruiz et Pavon, 1798 (Gratiolae, Plantaginaceae) was performed. This is the first study of nuclear DNA content carried out in the genus. Mitotic analysis revealed a base chromosome number x = 11 for all entities and different ploidy levels, ranging from diploid (2n = 2x = 22) to hexaploid (2n = 6x = 66). The results include the first report of the chromosome numbers for Mecardonia flagellaris (Chamisso & Schlechtendal, 1827) (2n = 22), Mecardonia grandiflora (Bentham) Pennell, 1946 (2n = 22), Mecardonia kamogawae Greppi & Hagiwara, 2011 (2n = 66), and Mecardonia sp. (2n = 44). The three ploidy levels here reported suggest that polyploidy is common in Mecardonia and appear to be an important factor in the evolution of this genus. The 2C- and 1Cx-values were also estimated in all the species. The 2C-values ranged from 1.91 to 5.29 pg. The 1Cx-values ranged from 0.88 to 1.03 pg. The general tendency indicated a decrease in the 1Cx-value with increasing ploidy level. The significance of the results is discussed in relation to taxonomy of the genus.