Low Hop Clover
Bean family (Fabaceae)
Description: This annual plant is up to 1' tall, branching frequently and having a bushy appearance. The stems are green or reddish green and pubescent; they have a tendency to sprawl. The alternate leaves are trifoliate; they have long petioles that are hairless. The leaflets are ovate or obovate, hairless, and slightly dentate along the margins. They have conspicuous pinnate veins that are straight, but lack any white chevrons. The petiole of the middle leaflet is conspicuously longer than the petioles of the lateral leaflets; the petioles of the latter are often sessile, or nearly so. Each leaflet is about ¾" long and half as much across.
From the axils of the upper trifoliate leaves, their develops individual flowerheads from pubescent stalks about 1" in length. Each of these stalks is longer than the petiole of the adjacent trifoliate leaf. The yellow flowerheads are up to ½" across. They are more or less spherical and consist of about 15-40 flowers. Each flower is about 1/6" (4 mm.) long. It has 5 elongated yellow petals and a light green calyx that is shorter than the petals and inconspicuous. The upper petal, or standard, has an outer surface that is conspicuously grooved; it is parallel to the keel (the lower petals) and functions like a protective hood. The blooming period occurs during the summer and lasts about 1-2 months. The petals of the flowers are persistent, turning light brown or nearly white on the flowerheads. Each flower produces a single seedpod that is shorter than the persistent keel. The root system consists of a taproot, which can form nodules on secondary roots to accommodate nitrogen-fixing bacteria. This plant spreads by reseeding itself, and often forms colonies.
Cultivation: The preference is full or partial sun, moist to mesic conditions, and a loam or clay-loam soil. It appears to favor fertile soil that is not too dry.
Range & Habitat: Low Hop Clover is a common plant that occurs in most counties of Illinois, where it is not native. Habitats include savannas, abandoned fields, pastures, edges of paths, degraded meadows with a history of disturbance, and vacant lots. This species is occasionally grown for forage or to rejuvenate cropland. It prefers disturbed grassy areas, although it occasionally invades natural areas to a limited extent. Low Hop Clover was introduced into the United States from Eurasia.
Faunal Associations: The flowers are pollinated primarily by various kinds of bees, which seek nectar and pollen. Beeflies, small butterflies, and skippers may visit the flowers as well. The caterpillars of several Colias spp. (Sulfur Butterflies) feed on Trifolium spp. (Clovers), as do the caterpillars of numerous moths (see Moth Table). Upland gamebirds feed on the seedheads and foliage of clovers, including the Ring-Necked Pheasant, Greater Prairie Chicken, and Wild Turkey. The foliage and seedheads are also eaten by various small mammals, including the Cottontail Rabbit, Groundhog, Thirteen-Lined Ground Squirrel, and Meadow Vole.
Photographic Location: A weedy meadow at Judge Webber Park in Urbana, Illinois.
Comments: This is the most common Hop Clover in Illinois. The flowers are bright lemon yellow and reasonably attractive. The other Hop Clovers that occur in Illinois, Trifolium aureum (Yellow Hop Clover) and Trifolium dubium (Small Hop Clover), are similar in appearance, except that the middle leaflets of their trifoliate leaves have petioles that are no longer than the lateral leaflets (they're often sessile, or nearly so). In Low Hop Clover, the petioles of the middle leaflets are conspicuously longer than the others. The common name of these species refers to the persistent flowers, which bend downward with maturity and become light brown or nearly white, causing the flowerheads to resemble the fruiting heads of Humulus spp. (Hops). Another species, Medicago lupulina (Black Medic), has similar flowers and foliage, although its coiled black seedpods are quite different in appearance. If the seedpods are unavailable for examination, it is still possible to distinguish Low Hop Clover from Black Medic by comparing the standards (upper petals) of their flowers. In Low Hop Clover, the outside of the standard (facing upward) has conspicuous grooves along its length, and it is held parallel to the length of the keel (the lower petals). In Black Medic, the standard lacks conspicuous grooves and it is held perpendicular to the length of the keel when the flower is fully open.