MORPHOLOGICALAND CHROMOSOMAL CHARACTERIZATION OF COMMELINA BENGHALENSIS L. (COMMELINACEAE) FROM ARGENTINA

Abstract

Commelina benghalensis is a small herb native to tropical Africa and Asia but introduced elsewhere. In America it was
found growing at open fields, border of woods and cultivated areas (south USA, Mexico, West Indies, French Guiana,
Brazil, Bolivia, Paraguay) as a weed or invasive plant and its difficult manage causes economic damages in diverse
agroecosystems all over the world. Commelina benghalensis was found at a border of Misiones´ forest (Argentina,
Misiones Province, Guaraní Departament, El Soberbio, 27º17’54.5’’S; 54º12’19’’W) and classical cytogenetic techniques
were applied in order to analyze its genetic system. Commelina benghalensis is a diploid with 2n = 2x = 22 median size
chromosomes (4.05 - 6.60 µm) and 55.04 µm/genome. Its karyotype, 8m + 10sm + 4st is unimodal (A2 = 0.14 / R = 1.63)
and slightly asymmetrical (A1 = 0.44 / i = 34.75 / r>2 = 0.55) (3A Stebbins category). Chromosome pair No. 11 (st) has
a terminal macrosatellite in the short arm and presumably carry the active NOR. Microsporogenesis is normal and
produces viable polen grains (>80%). Meiotic behaviour is regular. In PMC at diakinecis / metaphase I, 11 bivalents were
observed, mainly rings (92.7%) with distal chiasmata (96.7%) and an average of chiasmata / bivalent = 1.90. The meiotic
system in conjuntion with a particular breeding system promotes a high genetic homogeneity, and suggests that this
species has coadapted features with adaptative advantages allowing an invader behaviour.