Massimiliano Dematteis

Chromosome studies of some Vernonia species (Asteraceae)

Chromosomes of 12 Vernonia species (Asteraceae) from South America were studied. First counts were reported for: V. alpestris Gardn. (n = 17), V. chalybaea Mart. ex DC. (2n = 32), V. cotoneaster Less. (2n = 30), V. fruticulosa Mart. ex DC. (n = 16) and V. lithospermifolia Hieron. (n = 10, 2n = 20). Furthermore, in V. aurea Mart. ex DC. (2n = 32), V. mollissima D. Don (n = 32) and V. saltensis Hieron. (2n = 64) numbers different from those reported in the literature were found. Karyotypes were described for some species. V. aurea contains 24m + 8sm chromosomes, V. chalybaea contains 22m + 10sm chromosomes, V. cincta Griseb. 36m + 16sm + 8st and V. cotoneaster 18m + 12sm. The basic chromosome numbers x = 10, 14, 15, 16 and 17 were confirmed for South American Vernonia species. The results are discussed in relation to previous chromosome studies for the genus.

Karyotype analysis in some Vernonia species (Asteraceae) from South America

SUMMARYThe somatic chromosomes of eight Vernonia species (Asteraceae) from Brazil, Paraguay and Argentina were analyzed. First chromosome counts are presented for V. coriacea Less. (2n=32 = 20m + 10sm + 2st), V. dura Mart, ex DC. (2n=32 = 22m + 10sm), V. eriolepis Gardn. (2n=32 = 22m + 8sm + 2st), V. grandiflora Less. (2n=64 = 50m + 14sm) and V. onopordioides Baker (2n=32 = 18m + 2m-sm + 10sm + 2st). Besides, the chromosome numbers of V. brevifolia Less. ((2n=32 = 22m + 10sm) and V. sellowii Less. (2n=62 = 40m + 20sm + 2st) are also confirmed. The number found in V. saltensis Hieron (2n=64 = 48m + 16sm) support the occurrence of two cytotypes within the species, one diploid (2n=32) and the other tetraploid (2n=64). The eight species revealed certain differences between their karyotypes principally in formula, total length and asymmetry level, which coincides with earlier studies for South American taxa. Satellites were commonly found on submetacentric or subtelocentric pairs, being also variable in morpho...

Pollen morphology of some species of Vernonia s. l. (Vernonieae, Asteraceae) from Argentina and Paraguay

Pollen morphology is widely used in taxonomic treatments of tribe Vernonieae, and differences in exine structure and aperture form have been described for many species within the genera comprising the tribe. However, in recent years a number of new species have been described and, in the present paper, we describe in detail the pollen of 24 species of the tribe which are either endemic or uncommon to certain regions of Argentina or of Paraguay. The pollen of these species are radially symmetrical and more or less spheroidal, 3‐colporate or, in one species, 3‐porate; the exine may be tectate or semitectate and microperforate, with echinate lophae or, in the 3‐porate example, psilate lophae. Using a range of characteristics related to size, shape, wall thickness, apertures and tectum surface morphology, five of the six pollen types previously described for tribe Vernonieae, and a subtype, are recognized. Our results support the usefulness of pollen morphology in helping to determine the taxonomic position of species within tribe Vernonieae.

Karyotype analysis in eight species of Vernonia (Vernonieae, Asteraceae) from South America

Abstract The somatic chromosome number and karyotypes of eight species of Vernonia were analyzed. The results include the first chromosome count for V. hexantha Sch.Bip. (2n=30), which is diploid with base number x=15. The karyotypes are analyzed for the first time for two cytotypes of Vernonia cognata Less. (2n=40= 28m + 12sm; 2n=80= 48m + 32sm), V. hexantha (2n=30= 24m+6sm), V. membranacea Gardner (2n=34= 24 + 10sm), V. salzmannii DC. (2n=20= 10m + 10sm) and V. verbascifolia Less. (2n=20= 12m + 8sm). All the studied species showed a predominance of metacentric chromosomes, with a lower proportion of submetacentric pairs. In V. brevifolia Less. 0 to 3 accessory or B chromosomes were found. The chromosomes varying in length from 1.25 to 3.98 μm. The differences in the symmetry 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.

Karyotype analysis and DNA content in some species of Chrysolaena (Vernonieae, Asteraceae)

Cytogenetic characterization by karyotyping and determination of DNA content by flow cytometry of five species of Chrysolaena (Vernonieae, Asteraceae) was performed. This is the first study of nuclear DNA content realized in the genus. The 2C-values were compared with the ploidy level and the total karyotype length (TKL) of each species. Mitotic analysis revealed a base chromosome number x = 10 for all entities and different ploidy levels, from diploid (2n = 2x = 20) to octoploid (2n = 8x = 80). All species showed bimodal karyotypes composed of metacentric and submetacentric chromosomes. The average chromosome size (ML) varied from 1.86 μm to 2.70 μm, while the TKL ranged from 18.65 μm to 80.55 μm. The intrachromosomal asymmetry index (A1) varied from 0.27 to 0.38, while the interchromosomal asymmetry index (A2) ranged from 0.19 to 0.25. A new cytotype is reported for the first time for C. propinqua. Accessory chromosomes found in C. verbascifolia, C. cognata, C. flexuosa, and C. propinqua are also reported as new.

Pollen aperture heteromorphism in Centaurium pulchellum (Gentianaceae)

Pollen variations involving the number and position of the apertures are relatively frequent in certain members of Gentianaceae. In this paper the high incidence of pollen variation in Centaurium pulchellum (Sw.) Druce is described. Two other species of Centaurium: C. ameghinoi (Speg.) Druce and C. cachanlahuen (Molina) B. L. Rob were also examined. These two species have 3‐colporate or, less frequently, 4‐colporate pollen grains, which are the two basic aperture arrangements. However, there are also a variable proportion of atypical grains. Apart from typical 3‐zonacolporate grains, C. ameghinoi sometimes has 3‐syncolpate or parasyncolpate pollen, while C. cachanlahuen occasionally has 4‐colporate grains with short colpi that converge in pairs. C. pulchellum also has 3 or 4‐colporate grains, but a high proportion of the pollen grains show a range of different aperture patterns. A total of 13 aperture configurations, including the typical 3‐colporate and 4‐colporate types, were recorded. The proportion of the different pollen types varied widely between and within individuals. However, the production of atypical grains does not seem to have any notable effect on pollen viability within the species. It is suggested that the wide variation in aperture pattern observed in C. pulchellum may be partially induced by environmental factors.

Vernonanthura warmingiana (Asteraceae: Vernonieae), a new species from Brazil

A new species ofVernonanthura (Asteraceae),V. warmingiana, from the Brazilian states of Minas Gerais and São Paulo is described and illustrated. The new species resemblesVernonanthura laxa, but differs in having 15–20 florets per capitula, small leaves, the blades elliptic to lanceolate and rounded at the apex. In addition, a new synonym is reported forVernonanthura laxa, which is also described, and for the first time illustrated.ResumenUna nueva especie deVernonanthura (Asteraceae),V. warmingiana, de los estados brasileros de Minas Gerais y São Paulo es descrita e ilustrada. La nueva especie se asemeja aVernonanthura laxa, pero difiere por presentar 15–20 flores por capítulo, hojas de menor tamaño y lámina foliar elíptica o lanceolada, redondeada en el ápice. Además se presenta un nuevo sinónimo paraVernonanthura laxa, la cual también es descrita y por primera vez ilustrada.

Pollen morphology and implications for the taxonomy of the genus Chrysolaena (Vernonieae, Asteraceae)

This study aims at finding new morphological characters to evaluate the taxonomic position of species in the genus Chrysolaena (Vernonieae, Asteraceae) as suggested by the current classification of tribe Vernonieae. We have characterized the morphology of pollen grains in all 18 species of Chrysolaena. Results show that all the studied species possess pollen grains of type “C”, which is therefore characteristic of the genus. This pollen type is 3-colporate, echinolophate, oblate-spheroidal, with a total of 29 lacunae, including the polar lacuna, but lacking the equatorial lacuna. Chrysolaena is considered stenopalynous due to the fact that the pollen type in most of the species is similar. Nevertheless, variation in the size of pollen grains allowed us to identify three groups of taxa: small, medium-sized and large. Pollen morphology is a useful taxonomic marker, in addition to other morphological and molecular characters defining the genus.

Floral microcharacters in Lessingianthus (Vernonieae, Asteraceae) and their taxonomic implications

Micromorphological characters of 113 species of the South American genus Lessingianthus H.Rob. (Vernonieae, Asteraceae) were analyzed to evaluate their reliability as taxonomic markers. The corolla pubescence was studied in detail for the first time in the genus. Glandular and non-glandular trichomes were studied and described. The trichome types allow differentiation among related species, but do not reflect the relationships among species groups. On the other hand, the basal stylar node only occurs in a distinctive group of species within the genus. The apical appendage of the anthers is non-glandular in all species of the genus. Several character states analyzed in Lessingianthus are often widespread in other related genera of Vernonieae. Therefore, Lessingianthus can be circumscribed only by a combination of micro- and macromorphological features.

Chromosome number, meiotic behavior and pollen fertility of six species of Chrysolaena (Vernonieae, Asteraceae)

Chromosome number, meiotic behavior and pollen fertility were determined for six species of the genus Chrysolaena H.Rob. (Vernonieae, Asteraceae). All the species had a base chromosome number of x = 10, with somatic numbers that ranged between 2n = 20 and 2n = 60. The chromosome number of Chrysolaena obovata (Less.) Dematt. (2n = 4x = 40) and a new cytotype for C. lithospermifolia (Hieron.) H.Rob. (2n = 4x = 40) are reported for the first time. Normal meiotic behavior was observed for the diploid species C. platensis (Spreng.) H. Rob., C. propinqua (Hieron.) H. Rob. and C. flexuosa (Sims) H. Rob. However, the polyploid taxa C. obovata, C. lithospermifolia (tetraploid) and C. cognata (Less.) Dematt. (hexaploid) showed many meiotic irregularities such as multivalent formation, chromosomes outside plate, early segregation of chromosomes, laggards and bridges in anaphase and telophase. Pollen fertility was high in all species, however, including in the polyploids. Polyploidy is more common in Chrysolaena than in any other New World Vernonieae so far reported and appears to be an important factor in the evolution of this genus.