Supernumerary Chromosomes in Haplopappus validus (RYDB.) Cory

Supernumerary chromosomes (sc) in Haplopappus validus were studied with regard to their morphological and genetic effects and their mode of transmission. No morphological effects were observed with up to six sc, but fertility, as judged by percentage pollen stainability, is reduced with increasing numbers of sc. The sc tended to increase in number through the male line as a result of post-meiotic preferential distribution. Pollen with higher numbers of sc is apparently at a disadvantage in competition with pollen with few or no sc. Presence of sc in the section Isopappus of Haplopappus is correlated with the relative antiquity of taxa in the section, being most frequent in the most primitive taxon and apparently absent or rare in the two most recently evolved taxa.