URDAMPILLETA juan Domingo
Cytological study of Polystichum (Dryopteridaceae) species from Southern South America
MORENO, R.; CHIARINI, F.; URDAMPILLETA, J. D.; BARBOZA, G.; BARRINGTON, D.
AUSTRALIAN JOURNAL OF BOTANY
Lugar: Collingwood; Año: 2015 vol. 63 p. 403 - 414
Polystichum is one of the most diverse genera of ferns, with 360-400 species distributed worldwide. South America harbors ca. 40 species, clustered in three centers of diversity: the Northern and Central Andes (NCC), the Brazilian (BC), and the Southern South America Center (SSC). In order to increase our understanding of the systematic relationships within Polystichum, mitotic chromosomes and spore features were studied in nine species from Argentina and Chile. All species presented the basic number x = 41, with different ploidy levels (2x, 4x and 8x). In general, chromosomes were homogeneous in size (average length 2.50-5.75 µm) and mostly subtelocentric; centromeres were inconspicuous and secondary constrictions were frequently observed. All species presented 64 spores per sporangium, suggesting normal sexual reproduction. Significant differences in spore size were found among species and it was positively correlated with ploidy level. A relationship between sum total chromosome length and ploidy level was observed. However, there was also a reduction in single-chromosome length in the polyploids, pointing to genome downsizing. Our results agree with previous records, being diploids frequent among NCC species and absent among SSC species. In addition to sharing very specific morphological characters, SSC species are cytologically characterized by being polyploids (4x and 8x). A literature survey covering 116 species of Polystichum, revealed that Australian and New Zealand Polystichum species exhibit similarly high frequencies of polyploidy. In the case of P. tetragonum (2n = 164), endemic to the Juan Fernandez archipelago, our data suggest that it was originated by transoceanic migration from a South American ancestor, probably also tetraploid