Viguiera anchusaefolia var. immarginata

AGUILERA PM; DAVIÑA JR; HONFI AI

TAXON

INT ASSOC PLANT TAXONOMY

Lugar: Viena; Año: 2011 vol. 60 p. 1784 - 1784

0040-0262

Viguiera anchusaefolia var. immarginata (DC.) Blake n = 11, 2n = 22, 22 + 1B, 22 + 2B, CHN. Argentina, Misiones Province, Leandro N. Alem Department, along the road between the villages of Cerro Azul and Villa Venecia, 23 km SE of Paraná river, in open field, 27°36´ S, 55°34´ W, 29 Dec 2006, P.M. Aguilera 18 (MNES). Viguiera anchusaefolia (DC.) Baker naturally occurs in Argentina, in its northeast and central-east regions (Misiones, Corrientes, Entre Ríos and Buenos Aires Provinces), Brazil, and Uruguay. This species has a considerable morphological variability and two varieties can be distinguished, var. anchusaefolia and var. immarginata. Viguiera anchusaefolia var. immarginata exhibited n = 11 bivalents in PMC at diakinesis and metaphase I and chromosomes behaved regularly at meiosis. Our results differ from previous chromosome counts which reported n = 28, ca. 34, ca. 16–17 II in V. anchusaefolia. Our plant material is diploid with 2n = 2x = 22 chromosomes. Unexpectedly, in some individuals from this natural population we noticed 2n = 23 or 24 chromosomes, and also mitotic instability, that means, on the same slide, different cells from the same root tip bore 2n = 23 and 24 chromosomes. Therefore, a more exhaustive karyotype analysis was carried out and four cytotypes were recognized. The typical cytotype 2n = 22 possess a karyotype formula of 18 m + 4 sm chromosomes and this is the standard karyotype. Other three cytotypes possess additional chromosomes, namely BI and BII, in combinations 2n = 22 + BI, 2n = 22 + BII, or 2n = 22 + BI + BII. Chromosomes BI and BII are m and BI is slightly larger than BII. The smallest chromosome has 1.50 ± 0.07 μm (m) and the largest 2.37 ± 0.00 μm (m) with a mean chromosome length of 1.90 ± 0.02 μm. All karyotypes are unimodal (A2 = 0.14 ± 0.01; R = 1.58 ± 0.08) and symmetrical (A1 = 0.22 ± 0.01; r > 2 = 0,00; i = 43.42 ± 0.20; AI = 1.52 ± 0.06) (Stebbins´ category 1A of karyotype asymmetry). The haploid genome has 22.87 ± 1.23 μm. The occasional lack of a counterpart chromosome, observed mitotic instability and an earlier condensation along with heteropicnotic behavior throughout the cell cycle led us to propose that these extra chromosomes are B ones, which could help to explain the number diversity previously reported for this species.