Trifolium campestre
low hop clover [Blooms: May-Aug]
Low hop clover (Trifolium campestre) flowerheads. Lower right: a low hop clover flowerhead elevated on a fuzzy flower stalk; the stalk arises from the axil of the leaf in the background. Upper right: an immature low hop clover flowerhead. The green floret buds on the top of the flowerhead are still maturing; the yellow ones below are ready to entertain pollinators. Upper left: a mature low hop clover flowerhead with all pea-like florets open. Both the lateral petals and the keel are visible with a bit of searching. Bottom left: a brown stink bug (Euschistus servus) on a low hop clover flowerhead. This may give you a better idea of how tiny the florets really are. Note: on all the flowerheads pictured, the standard — the hood-like single petal — is markedly grooved/folded. A grooved standard is a diagnostic character for low hop clover, separating it from all other Jackson Park clovers.
Fuzzy flower stalks about 1″ long arise from the leaf axils of low hop clover. The flowerheads are roughly spherical, lemon yellow, and about 1/2″ across comprised of 20-40 pea-like florets with five petals; each floret is about 4 mm long. The upper petal (the standard) on each floret is conspicuously grooved and forms a hood over the two petals forming the keel; two lateral petals flank the keel. Fertilized florets form tiny seedpods that are shorter than the keel. The flower color and foliage of low hop clover are very similar to black medic (Medicago lupulina), but the standard on black medic is not grooved and sits perpendicular to the keel.
Low hop clover (Trifolium campestre) stems and leaves. Top: an image of a single leaf of low hop clover in the plane of the leaf (upper left) and another leaf face-on on the right. On the latter leaf, note the longer petiolule on the apical leaf than on the two lateral leaves, the pair of stipules at the base of the petiole, and the hairy stem and flower stalk. Lower right: a flower stalk arising from the axil of a leaf; the stipule is well displayed. Lower left: a single leaf of low hop clover showing the weak teeth along the leaflet margins.
Low hop clover is an exotic annual or biennial, native to Europe and western Asia; it was introduced as a forage crop and for “soil improvement” and is now naturalized in the U.S. As the name implies, it doesn’t grow very tall — 12″ or less. The stems are green or reddish green, slightly hairy, and round in section; they tend to sprawl. The leaves are alternate, palmately compound with three leaflets, each 1/2-3/4″ long and half as wide; the central (apical) leaflet has the longest petiolule, while the lateral leaflets have very short petiolules or are sessile. Unlike red clover (T. pratense) and white clover (T. repens), there are no white chevron marks on the leaflets. The leaflets have very low teeth along their margins where the lateral veins intersect the leaf margin. The stems have short, downy hairs, but the leaf petioles are hairless. Two stipules (bracts) flank the base of the leaf petioles; they are oval, half the length of the leaf petiole, and with a pointed end.
Low hop clover (Trifolium campestre) in the wild. The lower image of low hop clover was taken on a lawn west of Columbia Basin; the upper image is a closer view of low hop clover, here in Bobolink Meadow.
Low hop clover is an exotic annual or biennial, native to Europe and western Asia; it was introduced as a forage crop and for “soil improvement” and is now naturalized in the U.S. As the name implies, it doesn’t grow very tall — 12″ or less. The stems are green or reddish green, slightly hairy, and round in section; they tend to sprawl. The leaves are alternate, palmately compound with three leaflets, each 1/2-3/4″ long and half as wide; the central (apical) leaflet has the longest petiolule, while the lateral leaflets have very short petiolules or are sessile. Unlike red clover (T. pratense) and white clover (T. repens), there are no white chevron marks on the leaflets. The leaflets have very low teeth along their margins where the lateral veins intersect the leaf margin. The stems have short, downy hairs, but the leaf petioles are hairless. Two stipules (bracts) flank the base of the leaf petioles; they are oval, half the length of the leaf petiole, and with a pointed end. Fuzzy flower stalks about 1″ long arise from the leaf axils. The flowerheads are roughly spherical, lemon yellow, and about 1/2″ across comprised of 20-40 pea-like florets with five petals; each floret is about 4 mm long. The upper petal (the standard) on each floret is conspicuously grooved and forms a hood over the two petals forming the keel; two lateral petals flank the keel. Fertilized florets form tiny seedpods that are shorter than the keel. The flower color and foliage of low hop clover are very similar to black medic (Medicago lupulina), but the standard on black medic is not grooved and sits perpendicular to the keel.
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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)
