Trifolium campestre Schreb. (large hop-clover, Bishop clover)

T. procumbens L., an officially rejected name

Pl. 409 h, i; Map 1811

Plants annual, taprooted. Stems 5–40 cm long, erect or ascending (rarely prostrate), not rooting at the nodes, few- to much-branched, glabrous or with loosely appressed hairs. Leaves long-petiolate toward the stem base to short-petiolate near the tip, the longest petioles to 25 mm, longer than the leaflets. Stipules shorter than the associated petiole, ovate, fused to about the midpoint, the free portions angled or somewhat tapered at the tips, often somewhat membranous in the basal half between the veins, the margins more or less entire. Leaflets 4–16 mm long, 4–8 mm wide, the terminal leaflet with a stalk 1–3 mm long, the lateral leaflets sessile or nearly so, oblong-obovate, angled at the base, rounded to more or less truncate or shallowly notched at the tip, usually with a short broad tooth at the very tip, the margins shallowly toothed above the midpoint, the surfaces glabrous or the undersurface finely hairy, sometimes only along the midvein. Inflorescence 7–15 mm long, 7–10 mm wide, globose to ovoid or cylindric dense spikelike racemes, the stalk 5–90 mm long. Flowers (10–)20–40(–50), short-stalked, the stalk spreading or becoming reflexed at fruiting. Calyces 1.2–2.5 mm long, the tube 0.5–1.0 mm long, glabrous or sparsely hairy, the (longest) teeth 2–3 times as long as the tube, unequal (the lower teeth 2–3 times the length of the upper ones), slender and moderately (shorter teeth) to long-tapered (longer teeth), each tooth often tipped with 1 or 2 stiff hairs, lacking a prominent network of nerves and not becoming inflated at fruiting. Corollas 3.5–6.0 mm, longer than the calyx lobes, pale to bright yellow, the banner incurved, obovate, usually shallowly notched at the tip and with a slightly toothed margin, strongly parallel-nerved, especially with age. Fruits 2.0–2.5 mm long, oblong-ovoid, stalked, the outer wall papery, 1-seeded. Seeds 1.0–1.5 mm long, oblong-ellipsoid, yellow, shiny. 2n=14. April–September.

Introduced, common south of the Missouri River, widely scattered farther north (native of Europe; introduced widely elsewhere in the world, including most of the U.S., Canada). Banks of streams and rivers, margins of ponds, lakes, and oxbows, bases and tops of bluffs, disturbed portions of upland prairies, savannas, and glades; also fallow fields, old fields, pastures, lawns, levees, ditches, railroads, roadsides, and open disturbed areas.

Trifolium campestre is also called low hop-clover, pinnate hop-clover, Bishop clover, and small hop-clover. It and especially T. dubium often are confused with Medicago lupulina, which is encountered commonly in Missouri. That species differs from both of these clovers in its usually toothed stipules, nonpersistent corollas, and kidney-shaped, shiny, black fruits.

The Missouri collections are var. campestre. Two other varieties occurring within the native distribution have purplish corollas (Zohary and Heller, 1984).