The morphology of the pollen of the yacón

Its cytological relationships

Abstract

The pollen morphology of yacón (Smallanthus sonchifolius, Compositae, Heliantheae) polyploid with 2n = 58 chromosomes, a tuberous species cultivated in the Andes, and field yacón (Smallanthus macroscyphus) diploid 2n = 32 chromosomes, a wild relative from Southern Bolivia and North western Argentina, is analysed comparatively using optical and electronic scanning microscopy. The most relevant characters in S. sonchifolius are irregular and deformed pollen grains, short spines and with a thickness, in its annulo, superior to S. macroscyphys which has regularly formed pollen grains and normal-sized spines. Possible relationships between the pollen morphology and the polyploidy are established. These observations together with the cariologic records and the inviability of seeds and pollen would confirm the hypothesis about the hybrid origin of S. sonchifolius.