Interspecific size and number variation in pollen grains and seeds

An interspecific correlation between pollen grain size and seed size is demonstrated by means of the phylogenetic regression, which allows for phylogenetic bias. The correlation was not explained by plant size, mass of DNA per cell, style length or breeding system, although the first three of these factors all correlated with both pollen size and seed size. Two interpretations, involving pollen competition and flower size, are discussed. There is also an interspecific correlation between pollen grain number per flower and ovule number per flower. Some consequences of these correlations for the interpretation of pollen-ovule ratios and sex allocation strategies are considered.