Selfing and pollen allocation in some Asteraceae

Abstract

SynopsisSenecio vernalis and Calendula arvensis (Asteraceae) are two annuals which grow together in mixed populations and flower in Israel soon after the first winter rains. They were found to be potential selfers, without a self-incompatibility system. The average pollen production per floret and per flowering head was compared with the percentage of pollen with a known function or allocation: pollen grains deposited on stigmas, grains remaining in wilted florets, and non-viable pollen—overall totals of 24% in S. vernalis, 36% in C. arvensis. The remaining pollen (76% & 64%) is distributed according to fluctuating ecological factors, biotic (insects, etc.) and abiotic (rain, wind etc.). The outbreeding potential was assessed by study of the flowering phenology of florets and heads and the behaviour of pollinating insects, mainly flies. Considerable differences were found between the two species in most parameters. In both, especially C. arvensis, the probability of foreign pollen (i.e. pollen not from the same head) reaching the stigmas is very small. Pollenovule ratios for heads were found to be comparatively higher than those recorded for flowers with a similar rate of outbreeding. The efficiency of pollen transfer in the capitulum of the Asteraceae and the large investment in pollen are discussed.