Northern Ontario Plant Database

Plant Description

Salix ×fragilis L.

En: crack willow, brittle willow, snap willow
Fr: saule fragile
Oj: oziisigobimizh

Salicaceae (Willow Family)

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General: A large spreading deciduous tree, 3—20 m tall. The crack willow is an introduced hybrid from Europe, commonly planted and escaping along riverbanks, drainage ditches, and in abandoned fields. Crack willow's very brittle branches break off easily at the base during high winds and readily root in moist gravels or soils.

Taxonomy: Recent research has shown that crack willow, originally called Salix fragilis (without the ×) is actually a hybrid of the European Salix alba L. (white willow) and a willow from Asia Minor, Salix euxina I.V.Belyaeva, that was introduced to Europe. Salix ×rubens Schrank is a synonym of Salix ×fragilis.

Stems/twigs: Twigs slender, yellowish-green, greenish-brown, to reddish-brown; very finely hairy (puberulent), but becoming smooth and glossy with age (glabrate); buds are alternate, with a single reddish-brown bud scale that splits open along the surface adjacent to the stem. Leaf scars are narrowly U-shaped with 3 bundle trace scars. Multiple stout trunks are often present; bark is grayish-brown and deeply furrowed.

Leaves: Alternate, simple, pinnately-veined, short-petiolate, and barely stipulate. Petioles are 7—15 mm long, finely hairy, grooved above, and bear a pair of small rounded glands near the blade base. Leaf blades are lanceolate to narrowly elliptic, 7—15 cm long by 1—3 cm wide. Emerging leaves are yellowish-green and silky-hairy above, but become smooth with age (glabrate); mature blades are dark green, glabrous, and somewhat shiny above, but finely hairy along the midvein; the lower surface is pale and glaucous. Leaf bases are tapering (cuneate) to rounded, apices are sharply pointed (acuminate); and margins are flat and finely toothed (serrulate) with low rounded gland-tipped teeth. Lateral flowering shoots have leaves with entire margins. Leaves turn yellow in autumn.

Flowers: Unisexual, male and female catkins occur on different trees (plants dioecious); however, reproduction of Salix ×fragilis is mainly vegetative (rooting of broken stems). Flowering catkins are long and slender, arching to nodding, and emerge with the leaves at the end of short leafy lateral branches. Male (staminate) catkins are 3—6 cm long; each male flower has 2 stamens. Female (pistillate) catkins are 5—8 cm long; each female flower consists of a single short-stalked glabrous pistil on a short stalk (stipe) 0.5—1 mm long, a single short style, and 2-lobed stigmas. Both male and female flowers are subtended by small floral bracts, 0.8—1.3 mm long, oblong and pale yellow, with long silky hairs on the outer surface. Two small nectaries, about half the length of the floral bracts, are also present in each flower.

Fruit: An elongate cluster of small ovoid glabrous capsules, each 4.5—6 mm long. Willow capsules split along 2 lines; each half recurves to expose the minute seeds, which are rarely viable in this hybrid.

Habitat and Range: Planted or escaped along streambanks, in old fields or moist meadows. Crack willow is commonly seen along the North Shore of Lake Huron and in the Sault Ste. Marie area, but seldom occurs farther north; it is common throughout southern and eastern Ontario. Salix ×fragilis originated in Europe after Salix euxina, a willow native to Asia Minor (Turkey and Georgia) was introduced to Europe and formed hybrid swarms with the native European white willow, Salix alba (Belyaeva, I.V. 2009. Taxon 58: 1345).

Similar Species: Crack willow may be mistaken in Ontario for black willow (Salix nigra) Marshall, native in southern Ontario; black willow can be differentiated by its narrower lanceolate leaves, glabrous beneath, but not glaucous, and the prominent stipules at the base of each petiole.