1. Chamaecrista fasciculata (Michx.) Greene (showy partridge pea)

Cassia chamaecrista L.

Cassia fasciculata Michx.

Cassia fasciculata var. robusta (Pollard) J.F. Macbr.

Cassia fasciculata var. depressa (Pollard) J.F. Macbr.

Map 1690, Pl. 385 h, i

Stems 60–90 cm long, unbranched or few-branched from near or above middle, sparsely to moderately pubescent with short, curved or spreading hairs. Leaves 5–9 cm long, with 10–15 pairs of leaflets, the petiole 5–8 cm long, the petiolar gland 1.0–1.8 mm in diameter, sessile or occasionally short-stalked, located near the middle of the petiole. Stipules 7–16 mm long, 1–2 mm wide at the base, narrowly and usually asymmetrically lanceolate-triangular, long-tapered at the tip, with several prominent, parallel veins. Leaflets 10–20 mm long, 2–5 mm wide, narrowly oblong to oblong or occasionally oblong-elliptic, oblique at the base, abruptly tapered to a bluntly or sharply pointed tip, this sometimes with a minute, hairlike extension of the midvein, the margins with short, spreading hairs, the surfaces glabrous or hairy. Inflorescences axillary clusters of 1–3 flowers, with usually only 1 flower open at a time, the stalks 10–15 mm long, the bracts 3–6 mm long. Flowers somewhat asymmetrical, 25–30 mm in diameter. Sepals 10–12 mm long, 2–3 mm wide, lanceolate, sharply pointed, often hairy. Petals 15–20 mm long, 8–18 mm wide, broadly obovate, clawed, subequal, with one lateral petal curved around the stamens, the lower petal only slightly larger than the others, yellow or rarely white, some reddish-tinged toward the base. Stamens 10, unequal, with 9 smaller stamens grouped on one side of the pistil and 1 large stamen on the opposite side, the anthers 6–10 mm long. Ovary 4–5 mm long, hairy, the style 6–7 mm long. Fruits 3–6 cm long, 5–6 mm wide, sparsely to moderately hairy, especially along the margins, black when fully mature. Seeds 3.2–4.0 mm long, 2.0–2.4 mm wide, nearly square, the surfaces finely pitted, dark brown to black, not shiny. 2n=16. July–October.

Scattered to common nearly throughout the state (eastern U.S. west to South Dakota and New Mexico; Mexico). Glades, upland prairies, openings of mesic to dry upland forests, savannas, ledges and tops of bluffs, and banks of streams and rivers; also pastures, old fields, fallow fields, and roadsides.

Chamaecrista fasciculata is a widespread species, with populations that vary in growth habit and size, pubescence, leaflet number, gland characters, legume size, and anther color. These characters have been used singly and in combination to describe a number of varieties and forms, particularly in Florida, the Gulf Coast, and Texas (Turner, 1959; Correll and Johnston, 1970; Isely, 1975). However, Irwin and Barneby (1982) argued that most of this variation is not taxonomically useful, and they did not recognize any infraspecific taxa. Rare white-flowered plants from eastern Missouri have been called Cassia fasciculata f. jensenii E.J. Palmer & Steyerm.

Partridge pea has an interesting floral biology and ecology, reviewed by Gardner and Robertson (2000). The flowers open before dawn and close in the evening and have an unusual arrangement of floral parts. The petals are unequal in size, with the lowest petal the largest. There are 2 groups of stamens. One group of nine stamens arises from one side of the pistil. One of the lateral petals (called the cucullus), is rigid and curves around this group. The other stamen group consists of a single stamen that arises from the other side of the pistil, with a large, deflexed anther bent away from the other group. The style is thin and curved upward, to the left in some flowers and to the right in others. Styles and stigmas curved toward the left pick up pollen from the right side of the bee, and those curved toward the right receive pollen from the bees other side. The flowers produce no nectar, and the major pollinators are bumblebees. The bees land directly on the anthers, curve their abdomens over the terminal pores, squeeze the anthers, and vibrate their bodies to release the pollen, an activity referred to as buzz pollination. It has been suggested that the nine anthers enclosed in the cucullus serve as feeding anthers to attract the bees, whereas the single curved anther is involved in fertilization, although pollen in each group is equally viable. Experimental removal of the cucullus does inhibit fruit set, suggesting that the cucullus guides the bees (Wolfe and Estes, 1992).