Flower:

Male and female flowers are on separate plants (dioecious) in spike-like clusters (catkins) at the tips of short branchlets along 1 year old branches, emerging with the leaves; flowering from lateral buds continues for several more weeks. Male catkins are ¾ to 2½ inches long, the flowers densely to somewhat loosely packed, each flower with 2 yellow-tipped stamens that have a few hairs on the lower half of the stamen stalk (filament).

Female catkins are ¾ to 2½ inches long, the flowers loosely arranged on the spike, bottle-shaped with a long beak, hairless or silky hairy, and on slender stalks less than 1 mm long. At the base of each male and female flower stalk is a greenish to yellowish bract sparsely covered in short, crinkly hairs. The scales wither and drop off soon after flowering.

Leaves and stems:

Leaves are alternate, 2¼ to 6 inches long, 1/8 to 3/8 inch wide, 8 to 25+ times as long as wide, linear to narrowly oblong, pointed at the tip, tapering at the base, sharply toothed around the edges. The upper surface is medium to dark green, the lower surface about the same color. Leaf-like appendages at the base of the leaf stalk (stipules) are absent or obscure.

New leaves are sparsely to moderately covered in long, appressed, silky hairs on one or both surfaces and are green to yellowish or red-tinged, usually becoming hairless with age but the hairs may persist. New branchlets are hairless to variously hairy and yellowish to greenish, becoming hairless and orange-brown to red-brown or gray-brown the second year.

Stems are multiple from the base, have smooth to slightly rough gray bark and can reach 3½ inches diameter, occasionally taking the form of a small tree. Large, dense stands are often formed from numerous root suckers.

Fruit:

The spike elongates some as fruit matures, the fruit becoming more loosely arranged than the flowers.

Fruit is a capsule 5 to 10 mm long, yellowish when mature, hairless to silky-hairy, narrowly pear-shaped to club-shaped, inflated at the base with a long beak. The capsule splits into two halves when mature, releasing the cottony seed.

Notes:

There are over 20 species of Willows in Minnesota; Sandbar Willow is one of the most common species in the state, typically a large, multi-stemmed shrub and forming dense stands and large colonies; it may take the form of a small tree but this is uncommon. It is found in a variety of moist to wet places, usually in sandy, silty or loamy soil on lake and pond margins, river banks, marshes, prairie swales, floodplains and wet ditches, often with other Willow species. It has the narrowest leaves of all the Minnesota Willows, and leaves are about the same color green on both surfaces. Like other Willows, it first blooms in early May but will continue putting out catkins into July. These leaf characteristics and the continuous blooming separate it from all other Willows in the state.

In some references, Salix interior is treated as a subspecies of Salix exigua (subsp. interior). Per Flora of North America, S. exigua is considered a western species and their ranges do not naturally overlap. S. interior is known to hybridize with several other willows, but no hybrids have yet been recorded in the state.