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Many Achyrocline (Asteraceae, tribe Gnaphalieae) species are widely used in Argentina, Brazil and Uruguay as popular medicinal and aromatic plants. Achyrocline flaccida, A. satureioides, A. alata, and A. crassiuscula are distributed in Uruguay and popularly known as ‘marcelas’. In order to characterize them, we performed chromosome counts, compared the karyotypes, mapped the 5S and 45S rDNA sites by fluorescent in situ hybridization, and estimated their DNA content. All species were diploid with 2n = 28 chromosomes, this being the first report for A. flaccida and A. crassiuscula. All species showed symmetrical karyotypes composed exclusively of biarmed chromosomes. DNA content estimated by flow cytometry revealed 2C values ranging from 5.73 to 6.03 pg, the amounts for A. alata and A. crassiuscula being higher than those for the other species. Cytogenetic mapping of 5S and 45S rDNA sequences in three species, A. flaccida, A. satureioides and A. alata, showed that in these species both sites co-localized in the pericentromeric region of chromosome 10. This site corresponds to the only DAPI^– and CMA⁺ band of their genomes. Southern blot hybridization of 5S and 45S rDNA on BamHI digested genomic DNA confirmed the tight linkage of these rDNA families into a single unit. Cytological data indicate that Achyrocline species are karyologically poorly differentiated, whereas the uncommon distribution of 5S and 45S rDNA suggests a close relationship with other genera of the Anthemidae tribe.

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Adults and immatures of Parochlus carolinae n. sp. are described and figured. The specimens were collected from a stream and a river in the pampasic hills system in the centre-northern part of the San Luis Province, Argentina. The adult male is distinct in having hairy eyes. The pupa differs from other known species of the genus by the structure of the thoracic horn and the arrangement of setae on the anal spurs. The distribution of the genus Parochlus Enderlein is widened from an austral Andean Parochlus proper zone to a subtropical zone with Brazilian fauna.