Sandbar Willow is a small shrub, usually 3 meters or less in height. It forms colonies connected by shared root system so that many shrubs are found together.
For identification, Sandbar Willow has a distinctive leaf: long, 10 to 16 cm, narrow, and linear. No other willow has such long leaves compared to its width. The leaf blade is remotely denticulate (finely toothed, teeth widely spaced). The underside is slightly glaucous (blueish-white) underneath. Mature twigs are typically reddish-brown or yellowish brown.
Black Willow (S. nigra) and Crack Willow (S. x fragilis) also have long, narrow, finely toothed leaf blades, but Sandbar Willow’s teeth are well separated in comparison.
Sandbar Willow’s scientific name was S. exigua or S. exigua ssp. interior. Taxonomy has recently changed such that S. exigua (called Narrowleaf Willow) is now the western distribution and those in Ontario are S. interior (called Sandbar Willow).
There are few Ottawa area S. interior observations in iNaturalist, but in an area they can be locally common. They are most reliably found at Petrie Island.
Here are selected photographs with location coordinates in iNaturalist: