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

FARCO, G. E.; SOSA, M. M.; DEMATTEIS, M.; FERNÁNDEZ, A.

SOUTH AFRICAN JOURNAL OF BOTANY

ELSEVIER SCIENCE BV

Lugar: Johanesburgo; Año: 2012 vol. 78 p. 21 - 29

0254-6299

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