1. Senna marilandica (L.) Link (southern wild senna)

Cassia marilandica L.

C. medsgeri Shafer

Map 1696, Pl. 386 a, b

Plants perennial herbs, with a somewhat woody, often horizontal, branched rootstock, not or only slightly fragrant when bruised or crushed. Stems 1 to several, 100–200 cm long, erect or ascending, unbranched, glabrous or sparsely pubescent with spreading hairs toward the tip, sometimes somewhat glaucous. Leaves with the petiole 3–6 cm long, the petiolar gland positioned near the base, 1–2 mm long, ovoid to hemispherical or more or less short-cylindrical, appearing sessile and broadest at or below the midpoint. Leaf blades 14–20 cm long, with 8–10 pairs of leaflets. Leaflets 3.0–6.5 cm long, 10–25 mm wide, oblong to oblong-elliptic, oblique at the base, abruptly short-tapered to a minute, sharply pointed tip, the margins with a pale, narrow band and short, ascending hairs, the surfaces glabrous or the undersurface with scattered microscopic glandular hairs (at least when young), the undersurface also pale and somewhat glaucous. Inflorescences with 6–9 flowers, the flower stalks 10–15 mm long. Sepals somewhat unequal in size, variously 4–8 mm long, 3–4 mm wide, ovate, bluntly pointed at the tip, the margins short-hairy. Petals 7–12 mm long, 4–5 mm wide, oblanceolate to obovate. Stamens with the anthers purplish brown. Ovary 4–6 mm long, with short, appressed hairs, the style 2–3 mm long. Fruits 6–9 cm long, 7–10 mm wide, arched downward at maturity, strongly flattened, sparsely to moderately hairy when young, becoming glabrous at maturity, relatively conspicuously impressed between the seeds, dark brown to black at maturity. Seeds 4–5 mm long, 2.2–3.0 mm wide, oblong-obovate to obovate, slightly flattened, the surface often developing a fine network of cracks toward the margins at maturity, olive green to brown, more or less dull, the pleurogram usually slightly grayer than the remainder of the seed. 2n=28. July–August.

Scattered south of the Missouri River, less commonly farther north (eastern U.S. west to Nebraska and Texas). Banks of streams and rivers, sloughs, bottomland and upland prairies, bottomland forests, mesic upland forests, bases, ledges, and tops of bluffs, glades, and savannas; also pastures, old fields, fallow fields, roadsides, and open, disturbed areas.

Senna marilandica occasionally is cultivated as an ornamental in gardens for its attractive foliage and flowers. It is closely related to S. hebecarpa (Fernald) H.S. Irwin & Barneby (northern wild senna), which is widespread in the northeastern United States and adjacent Canada west to Wisconsin, Illinois, and eastern Tennessee, possibly also sporadically farther south. The two species are northern and southern analogs that have sometimes been confused (Isely, 1998) but have a broad region of geographic overlap in which they appear to maintain themselves consistently without apparent intermediates or hybridization. Senna hebecarpa differs in its ovary with dense, somewhat tangled, spreading hairs (vs. appressed-ascending hairs) and its petiolar glands, which are more or less club-shaped and widest above the middle (vs. hemispherical to short-cylindrical). A single historical Missouri specimen of S. hebecarpa exists in the herbarium of the Missouri Botanical Garden. It was collected by Mrs. James R. Bettis from the parsonage grounds of a church in Webster Groves (St. Louis County) in 1925 and was originally determined as Cassia marilandica. This specimen was deaccessioned by Robert Woodson and sent to the University of Minnesota herbarium during the early 1950s as part of his infamous purge of so-called superfluous sheets from the Missouri Botanical Garden (Solomon, 1998). It was thus potentially unavailable for Julian Steyermark to examine during his research on the Missouri flora. The specimen was returned to St. Louis in 1993 as part of a generous effort on the part of the staff in Minnesota to repatriate some 75,000 specimens they had received from Woodson. Upon its return, the plant was redetermined correctly as S. hebecarpa by Ron Liesner of the Missouri Botanical Gardens herbarium staff. The circumstances surrounding the original collection cannot be determined from the sheet, but it seems likely that the plant from which the flowering branch tip was pressed was under deliberate cultivation, rather than a spontaneous weed. Thus, at least for now, this species remains excluded from the Missouri flora. However, botanists working particularly in northeastern Missouri eventually may discover it growing in a natural habitat in the state.