Notes on the Taxonomy of Salix vitellina (Salicaceae).

Salix vitellina L., or golden willow, was described by C. Linnaeus in 1753. It was later considered to be affiliated with S. alba, and its taxonomic rank has been changed to variety, subspecies, and form. A recent proposal designated it as a form of S. alba × S. fragilis. The goal of this study was to verify the taxonomic designation of S. vitellina using morphological characteristics including ovule number. A few specimens of S. vitellina from Europe and North America, including the lectotype LINN1158.13, were analyzed. It was recorded that S. vitellina has an ovule index of 6-10, with most valves with four and five ovules and less than 50% of valves with five ovules. These ovule parameters were similar to those of S. alba. The other floral characteristics also indicated that S. vitellina is associated with S. alba. No signs of androgyny or flower aberrations, commonly occurring in willow hybrids, were found in the specimens of S. vitellina. Thus, the analyses did not corroborate the hybrid origin of S. vitellina. The ovule analysis also confirmed that f. chermesina with orange-red stems is also a taxon of S. alba, which differs from f. vitellina by a greater ovule index of 12-16.

The Ovule Number Variation Provides New Insights into Taxa Delimitation in Willows (Salix subgen. Salix; Salicaceae).

Salix babylonica, S. alba and S. fragilis are closely related species characterized by the lanceolate, acuminate and serrulate leaves. The boundaries between them are defined by relatively few diagnostic characters, and their identification is not fully solved. Recent studies have demonstrated that the number of ovules present in the ovaries of the willow flower can assist in the identification of the species. The detailed ovule data, characteristic for flowers of each species, S. babylonica, S. alba and S. fragilis, and variation in the number of ovules per ovary were documented using many representatives of these species from various geographic regions. The data included the minimum and maximum number of ovules per valve and per ovary and the percentages of valves with a specific number of ovules in a catkin. Some intermediate genotypes and clusters with similar ovule indexes were observed. The important character for the identification of S. babylonica was the presence of valves with 1 or 2 ovules in the ovaries; S. fragilis had valves with 3 ovules while S. alba had the greater number (4-12).