Karyotype studies in South American species of Solanum subgen. Leptostemonum (Solanaceae).

Mitotic chromosome numbers and karyotypes of 13 South American species (12 native and one naturalized) from four sections of SOLANUM subgen. LEPTOSTEMONUM were studied. Chromosome numbers of S. ACERIFOLIUM, S. AENICTUM, S. CONDITUM, S. CONSIMILE, S. INCARCERATUM, and S. PLATENSE are reported for the first time. The number 2n = 24 was found in most species, while 2n = 22 was found in S. MAMMOSUM and S. PLATENSE. The latter is the second SOLANUM with this unusual number. Satellites are always present and were visible in more than 50 % of the cells studied. Karyotypes are symmetrical: M and SM chromosomes are common, whereas ST chromosomes are rare. The karyotypes of S. AENICTUM, S. MAMMOSUM, and S. PANICULATUM are comparatively asymmetrical. Species can be distinguished by a combination of chromosome number, karyotype formulae, karyotype length, the position of satellites in a particular chromosome pair, and asymmetry indices. The phenogram obtained does not reflect the sectional arrangements or the systematic affinities of the species studied. In sect. ACANTHOPHORA, increased asymmetry is associated with derived characters (strong andromonoecy, winged seeds, mammiform fruits). Diversification in the subgenus is suggested to be related to visible chromosome rearrangements and cumulative, cryptic structural changes may have also played a relevant evolutionary role.