Carl Linnaeus first described a willow species as "
Salix fragilis" in 1753. It was later discovered that he was actually describing a species that he had also called
Salix pentandra. Since at least the 1920s, botanists have applied Linnaeus's name "
Salix fragilis" to both a pure species and to its hybrid with
Salix alba. In 2005, it was proposed that "
Salix fragilis" should be
conserved for the pure species, with the hybrid called "
Salix ×
rubens". The alternative was to conserve "
Salix fragilis" for the hybrid, with the pure species requiring a new name. Following a discussion, the Nomenclature Committee for Vascular Plants rejected the initial proposal in 2009 and opted to conserve the name "
Salix fragilis" for the hybrid. Irina V. Belyaeva subsequently described the previously unnamed parent species as
Salix euxina, and designated a
lectotype for the hybrid. The lectotype was shown by molecular evidence to be the hybrid between
S. alba and
S. euxina, the name of which is written as
Salix ×
fragilis to show its hybrid status.
Varieties S. ×
fragilis is very variable, with forms linking both parents. Some formally named varieties include the following. , none were accepted at this rank by
Plants of the World Online, being treated as synonyms of the species.
Clive A. Stace suggested some would be better treated as cultivars. •
S. ×
fragilis var.
decipiens W.D.J.Koch (
S. ×
decipiens Hoffm.) – assigned to
S. ×
fragilis by Plants of the World Online and by Belyaeva, but to
S. euxina by Stace •
S. ×
fragilis var.
furcata Ser. ex Gaudin – male tree with relatively wide leaves; of cultivated origin •
S. ×
fragilis var.
fragilis – male and female trees known; leaves with even, well spaced teeth •
S. ×
fragilis var.
glauca Spenn. •
S. ×
fragilis var.
polyandra Wimm. •
S. ×
fragilis var.
rubens (Schrank) P.D.Sell •
S. ×
fragilis var.
russelliana (Sm.) W.D.J.Koch – Bedford willow; female tree with long narrow leaves having somewhat uneven teeth; of cultivated origin ==Ecology==