- It’s a big genus. Salix rivals Carex in terms of the sheer number of species worldwide, about 350 extant and another 170 or so hybrids. VASCAN lists 91 occuring in Ontario; Michael Oldham lists 28 species found in Ontario’s Carolinian zone. Research Gate: https://www.researchgate.net/publication/317731067_List_of_the_Vascular_Plants_of_Ontario’s_Carolinian_Zone_Ecoregion_7E
- There is a lot of variation within species, mostly due to environmental and seasonal influences.
- Willow species hybridize, although occurences of hybridization have often been over-estimated.
- Willows are dioecious. This means that flowers of only one sex occur on a single individual. Most references provide a single key using staminate (male), pistillate (female), and vegetative characteristics.
- Willow flowers are very simple. In any one individual flower there are relatively few floral characteristics on which to draw for identification.
- The same species can look very different depending on the stage of development / time of year. For example, first leaves (which emerge from overwintered buds) and new leaves (produced later in the season) are quite different in terms of stipule size, density and colour of leaf hair (if present).
References: Argus (1986 and 2006), Meikle (1984)