Calculation of the ovule number in the genus Salix: A method for taxa differentiation

PREMISE: Recent investigations have demonstrated that the number of ovules present in the ovaries of the willow flower (Salix spp., Salicaceae) can be used to confirm the identification of species and hybrids. We present the method to calculate the ovule number, along with examples demonstrating its use for both species and hybrid verification. METHODS AND RESULTS: The best time to obtain a reliable ovule count is at the beginning of anthesis before numerous hairs develop in the ovary or after seed dispersal when the funiculi on the placenta can be counted. The ovules in all of the ovaries of one catkin should be counted, and the ovule index is recorded as their minimum–maximum range. The ovule number of a hybrid is the statistical mean of the ovule number of its parents. CONCLUSIONS: Ovule quantification is a useful tool that, in conjunction with traditional morphological and modern molecular techniques, presents additional evidence to support taxonomic decisions. The ovule number can also assist in species identification, classification, and in hybridization studies to verify the parentage of willow hybrids.