Salix eriocephala
Missouri River willow [Blooms: Apr]
Missouri River willow (Salix eriocephala) flowers. Top right: male catkins of Missouri River willow. Note the white filaments and yellow anthers of the stamens. Top left: female catkins of Missouri River willow. The individual female florets are flasks-shaped and green with a long, tapering beak; the reddish style/stigma protrudes from the tip of the beak. Bottom: a series (probably a clone) of Missouri River willows in the spring, all female.
Missouri River willow is dioecious — male and female florets (in the form of spike-like catkins) occur on separate plants. Catkins arise on one-year-old branches at about the same time as the leaves begin to emerge. Male catkins may be 1/2-2″ long; each floret has two stamens with yellow anthers on their tips. Female catkins range from 3/4-2.5″ long; the florets are yellowish-green and vase- or flask-shaped with an inflated base and a long beak that has a single protruding style. Both male and female catkins have a very small brown or bicolored bract at their bases that is covered with long, white hairs. After fertilization, female florets elongate as the catkin also elongates; the fruit is a yellowish to reddish green, hairless capsule, generally pear-shaped with a long beak. On maturity, the capsule splits to release seeds with long, attached, cottony hairs.
Missouri River willow (Salix eriocephala) stems and leaves. Top right: year-old branches with the characteristic yellowish bark in mid-April. A few male catkins can be seen in the upper right corner of the image (arrows); the leaves are just beginning to emerge. Top left: a stem with leaves in mid-June; note the characteristic stipules flanking the insertion of the leaf petiole on the stem. Bottom left: another stem with leaves and stipules. The two inserts show the stipules from different angles and different magnification. Bottom right: a fully developed leaf in mid-June. The upper image shows the top surface of the leaf; the lower image shows the underside of the same leaf.
Missouri River willow is a shrubby native willow that can be as large as 20 feet but is usually much shorter (less than 10 feet). New (first year) stems are green and covered with fine hairs but tend to lose the hairs afterwards and turn either reddish-brown (typical Missouri River willow) or yellowish tan (the “heart-leaved willow” type). Older stems develop a grey, rough bark and may reach 8″ in diameter. The leaves are alternate, 1-6″ long and about 1/5 as wide, lance-shaped with a fine tip and rounded base and with fine, rounded serrations on the leaf margins. The upper surface of the leaf is a medium or dark green; the underside is paler. Flanking the base of the petioles, where they insert on the stem, is a pair of large stipules that nearly encircle the stem. The stipules on Missouri River willow are similar to those seen on black willow (Salix nigra); compare the two species carefully before settling on a final identification.
A dense Missouri River willow (Salix eriocephala) shrub in one of the natural areas at 63rd St. Beach at the top of the dune line above the foreshore.
Missouri River willow is a shrubby native willow that can be as large as 20 feet but is usually much shorter (less than 10 feet). New (first year) stems are green and covered with fine hairs but tend to lose the hairs afterwards and turn either reddish-brown (typical Missouri River willow) or yellowish tan (the “heart-leaved willow” type). Older stems develop a grey, rough bark and may reach 8″ in diameter. The leaves are alternate, 1-6″ long and about 1/5 as wide, lance-shaped with a fine tip and rounded base and with fine, rounded serrations on the leaf margins. The upper surface of the leaf is a medium or dark green; the underside is paler. Flanking the base of the petioles, where they insert on the stem, is a pair of large stipules that nearly encircle the stem. Missouri River willow is dioecious — male and female florets (in the form of spike-like catkins) occur on separate plants. Catkins arise on one-year-old branches at about the same time as the leaves begin to emerge. Male catkins may be 1/2-2″ long; each floret has two stamens with yellow anthers on their tips. Female catkins range from 3/4-2.5″ long; the florets are yellowish-green and vase- or flask-shaped with an inflated base and a long beak that has a single protruding style. Both male and female catkins have a very small brown or bicolored bract at their bases that is covered with long, white hairs. After fertilization, female florets elongate as the catkin also elongates; the fruit is a yellowish to reddish green, hairless capsule, generally pear-shaped with a long beak. On maturity, the capsule splits to release seeds with long, attached, cottony hairs. Willows hybridize often and Missouri River willow is known to hybridize with seven other willows and suspected to have hybridized in a number of additional cases. Heart-leaved willow (Salix rigida) is very similar to Missouri River willow and Illinois Wildflowers recognizes the two as distinct based on some minor characters (size of the shrub, small differences in the width of the leaf), but Minnesota Wildflowers disagrees and ITIS.gov does not recognize Salix rigida as a distinct species. The stipules on Missouri River willow are similar to those seen on black willow (Salix nigra); compare the two species carefully before settling on a final identification.
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