Salix nigra
black willow [Blooms: ??]
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Black willow is dioecious — the plants produce either all male or all female inflorescences (catkins) on one-year-old branches; the catkins emerge with the leaves. Male catkins are 1-3″ long, cylindrical, yellow to greenish-white, and usually curved. Female catkins are greenish, 1-3″ long, elongating as they mature. Both male and female florets are numerous and arranged in pseudo whorls around the axis of their respective catkins; neither has either sepals or petals. Individual male florets have 3-6 stamens with yellow, globose anthers and a pale yellow, oval basal bract shorter than the stamens. Individual female florets also have a pale yellow, oval basal bract; a hairless, flask-shaped pistil 3-5 mm long is elevated above the bract on a 0.5-1.5 mm long (short!) pedicel and has a single style and a pair of stigmas at its tip. After fertilization, a capsule enlarges, finally splitting longitudinally to release the seeds with their attached cottony hairs.
More information
Black willow is a native species that can be a very large tree (30-90 feet tall), often with multiple trunks, but you are more likely to encounter younger specimens. The bark on old plants is gray to nearly black and sculpted with deep furrows; on younger trees, the trunk bark is grayish-brown with shallow furrows where the tops of the ridges are flattened; branches often have bark peeling in plates. Twigs are pale brown and smooth; shoots are light green and hairy. The leaves are alternate, 3-5″ long, 6-16 mm wide, lance-shaped, widest below the middle of the leaf, with very short (less than 1/4″), light green petioles; the margins bear serrated teeth with rounded tips. Note the distinctive “labryinth” leaf venation on black willow. The upper surface of the leaves is medium to dark green; the underside is only slightly paler. A pair of stipules, oval with ear-like lobes, flank the insertion of the petiole on the stem.
More information
Black willow is a native species that can be a very large tree (30-90 feet tall), often with multiple trunks, but you are more likely to encounter younger specimens. The bark on old plants is gray to nearly black and sculpted with deep furrows; on younger trees, the trunk bark is grayish-brown with shallow furrows where the tops of the ridges are flattened; branches often have bark peeling in plates. Twigs are pale brown and smooth; shoots are light green and hairy. The leaves are alternate, 3-5″ long, 6-16 mm wide, lance-shaped, widest below the middle of the leaf, with very short (less than 1/4″), light green petioles; the margins bear serrated teeth with rounded tips. Note the distinctive “labryinth” leaf venation on black willow. The upper surface of the leaves is medium to dark green; the underside is only slightly paler. A pair of stipules, oval with ear-like lobes, flank the insertion of the petiole on the stem. Black willow is dioecious — plants produce either all male or all female inflorescences (catkins) on one-year-old branches; the catkins emerge with the leaves. Male catkins are 1-3″ long, cylindrical, yellow to greenish-white, and usually curved. Female catkins are greenish are 1-3″ long, elongating as they mature. Both male and female florets are numerous and arranged in pseudo whorls around the axis of their respective catkins; neither has either sepals or petals. Individual male florets have 3-6 stamens with yellow, globose anthers and a pale yellow, oval basal bract shorter than the stamens. Individual female florets also have a pale yellow, oval basal bract; a hairless, flask-shaped pistil 3-5 mm long is elevated above the bract on a 0.5-1.5 mm long (short!) pedicel and has a single style and a pair of stigmas at its tip. After fertilization, a capsule enlarges, finally splitting longitudinally to release the seeds with their attached cottony hairs. Black willow also prefers moist to wet soils. The stipules on black willow are similar to those seen on Missouri River willow (Salix eriocephala); compare the two species carefully before settling on a final identification.
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![Evening primrose — clusters of yellow flowers occur at the apex of the plant. The flowers are 1-2" across, with four 1/2-1" long green sepals strongly reflected over a long (3/4-2"), green, cylindrical floral tube (the ovary is located just above the leaf axil), four heart-shaped yellow petals, eight stamens, and a single style with an X-shaped stigma. The sepals typically remain connected (in pairs) along one edge until the flower opens. The seedpods develop within the ovary (the base of the elongate floral tube); they are hairy, urn-shaped with rounded edges, and have four or eight small lobes on the apex. The seeds are claimed to remain viable in the soil for up to 70 years. The flowers open at dusk and close early in the day. — — — There are (at least) three evening primroses in Jackson Park — common evening primrose (Oenothera biennis), northern evening primrose (Oenothera parviflora), and hairy evening primrose (Oenothera villosa). They are easily confused with each other. (Judging by the conflicts between the accounts on Illinois Wildflowers [https://www.illinoiswildflowers.info/], Minnesota Wildflowers [https://www.minnesotawildflowers.info/], and Missouri Plants [http://www.missouriplants.com/], even the experts are confused.) All three species have yellow flowers with an X-shaped stigma, reflected sepals, petals with a small notch in their apex, stems that may be red or green, and lance-shaped leaves with short, widely-spaced teeth. Northern evening primrose is distinguished by (1) the presence of a knob or ridge at the tip of each sepal which the other two species lack (2) a seed capsule with four robust, flaring lobes with rounded tips at the apex of the seed capsule, and (3) a stigma that is very robust and almost fills the opening of the flower. Northern evening primrose has green to yellowish-green sepals. Hairy evening primrose (often but not always) has (1) striped or reddish-tinged sepals (check the buds where this character is often easier to see), (2) flowers that turn orange as they begin to senesce (although the reliability of this character is uncertain), and (3) always has glandular hairs covering the ovary that have "pimple-like" bright-red bases; these red pimples may also occur on the stems. All three species are somewhat similar to prairie sundrop (O. pilosella); the latter has very hairy stems and leaves, and translucent lines that radiate from the base of the petals in the flowers.](https://jacksonparkwildflowers.info/wp-content/uploads/2025/03/Oenothera_biennis-1t-300x300.jpg)
![Northern evening primrose flowers are 3/4-1.5" across, have four yellow, heart-shaped petals, eight yellow stamens, and a cross-shaped stigma on a modest style; the stamens are as long or longer than the petals and the stigma is nearly fills the floral opening. At the base of the flower are four sepals 1/2-1" long, that bend back along the 3/4-1.5" long floral tube as the flower develops with pairs of sepals attached along one edge until the flower opens. Only northern evening primrose with a distinct ridge or knob near the tips of the sepals. The seed capsule develops from the ovary; it is 3/4-1.5" long, cylindrical but tapering slightly towards the tip, with four robust, flaring lobes at the tip. — — — There are (at least) three evening primroses in Jackson Park — common evening primrose (Oenothera biennis), northern evening primrose (Oenothera parviflora), and hairy evening primrose (Oenothera villosa). They are easily confused with each other. (Judging by the conflicts between the accounts on Illinois Wildflowers [https://www.illinoiswildflowers.info/], Minnesota Wildflowers [https://www.minnesotawildflowers.info/], and Missouri Plants [http://www.missouriplants.com/], even the experts are confused.) All three species have yellow flowers with an X-shaped stigma, reflected sepals, petals with a small notch in their apex, stems that may be red or green, and lance-shaped leaves with short, widely-spaced teeth. Northern evening primrose is distinguished by (1) the presence of a knob or ridge at the tip of each sepal which the other two species lack (2) a seed capsule with four robust, flaring lobes with rounded tips at the apex of the seed capsule, and (3) a stigma that is very robust and almost fills the opening of the flower. Northern evening primrose has green to yellowish-green sepals and is the only one of the three evening primroses to (sometimes) have reddish color on some or all of the midvein of the leaves. Hairy evening primrose (often but not always) has (1) striped or reddish-tinged sepals (check the buds where this character is often easier to see), (2) flowers that turn orange as they begin to senesce (although the reliability of this character is uncertain), and (3) always has glandular hairs covering the ovary that have "pimple-like" bright-red bases; these red pimples may also occur on the stems. All three species are somewhat similar to prairie sundrop (O. pilosella); the latter has very hairy stems and leaves, and translucent lines that radiate from the base of the petals in the flowers.](https://jacksonparkwildflowers.info/wp-content/uploads/2025/03/Oenothera_parviflora-1t-300x300.jpg)
![Hairy evening primrose produves an elongating spike of flowers arises from the apex of the stem; flowers bloom near the tip while older flowers and seed capsules develop below. Individual flowers are 3/4-1.5" across; they sit on a long floral tube with the ovary at its base (attached to a leaf axil). The flowers have four yellow, heart-shaped petals, eight yellow stamens, and a cross-shaped stigma on a modest style; at the base of the flower are four sepals 3/8-3/4" long, reflected back along the floral tube as the flower develops with pairs of sepals attached along one edge until the flower opens. The sepals are often red-striped or red-tinged. Note the long, hairy floral tube below the sepals, the reddish stem, and glandular hairs with red bases on the ovary. The seed capsule develops from the ovary; it is up to 1.75" long, cylindrical but tapering slightly towards the tip, with four tiny lobes at the tip. — — — There are (at least) three evening primroses in Jackson Park — common evening primrose (Oenothera biennis), northern evening primrose (Oenothera parviflora), and hairy evening primrose (Oenothera villosa). They are easily confused with each other. (Judging by the conflicts between the accounts on Illinois Wildflowers [https://www.illinoiswildflowers.info/], Minnesota Wildflowers [https://www.minnesotawildflowers.info/], and Missouri Plants [http://www.missouriplants.com/], even the experts are confused.) All three species have yellow flowers with an X-shaped stigma, reflected sepals, petals with a small notch in their apex, stems that may be red or green, and lance-shaped leaves with short, widely-spaced teeth. Northern evening primrose is distinguished by (1) the presence of a knob or ridge at the tip of each sepal which the other two species lack (2) a seed capsule with four robust, flaring lobes with rounded tips at the apex of the seed capsule, and (3) a stigma that is very robust and almost fills the opening of the flower. Northern evening primrose has green to yellowish-green sepals. Hairy evening primrose (often but not always) has (1) striped or reddish-tinged sepals (check the buds where this character is often easier to see), (2) flowers that turn orange as they begin to senesce (although the reliability of this character is uncertain), and (3) always has glandular hairs covering the ovary that have "pimple-like" bright-red bases; these red pimples may also occur on the stems. All three species are somewhat similar to prairie sundrop (O. pilosella); the latter has very hairy stems and leaves, and translucent lines that radiate from the base of the petals in the flowers.](https://jacksonparkwildflowers.info/wp-content/uploads/2025/03/Oenothera_villosa-1t-300x300.jpg)
