Cytology and embryology of the pompom weed Campulochinum macrocephalum (Eupatorieae, Asteraceae)

GABRIELA E FARCO, MARÍA M SOSA, MASSIMILIANO DEMATTEIS, AVELIANO FERNÁNDEZ.

SOUTH AFRICAN JOURNAL OF BOTANY

ELSEVIER SCIENCE BV

Lugar: Yohannseburgo; Año: 2011 vol. 78 p. 21 - 29

0254-6299

Campuloclinium macrocephalum (Less.) DC. is a perennial herb widely distributed in the New World, but introduced to South Africa, where itis commonly called ?pompom weed?. This species is considered one of the most important weeds from Brazil and it has been included among theplant invaders of South Africa. Results of the meiotic and embryological analyses of six populations of C. macrocephalum are reported in thispaper. The microsporogenesis analysis revealed five triploid (2n=3x=30) and one diploid (2n=2x=20) populations with a basic chromosomenumber x=10. The diploid specimens showed regular meiotic behavior, but the triploid plants presented irregular chromosome pairing whichresult in the formation of univalents, bivalents and trivalents at diakinesis. In consequence, laggard chromosomes, unbalanced nuclei andmicronuclei were observed in subsequent phases of meiosis. The embryological analysis showed that the triploid specimens of C. macrocephalumhave embryo sac development from a nucellar cell (apospory), which indicates that these specimens are apomictic. Almost all cases of apomixisfound in tribe Eupatorieae are diplosporous apomixis. Campuloclinium macrocephalum constitutes the second species of the tribe and the first ofthe genus with apospory as reproductive system. The aposporous apomixis combined with the presence of xylopodium would be two importantfactors responsible for the invasiveness of C. macrocephalum.