35. Carex decomposita Muhl.

Pl. 38 j–n; Map 148

Plants monoecious, with short or poorly developed rhizomes, forming dense clumps. Vegetative stems usually poorly developed, reduced to basal clusters of leaves. Flowering stems 40–100 cm long, erect, bluntly trigonous, glabrous, dark brown to nearly black at the base. Leaves basal and on the basal half of the stems, glabrous, the uppermost leaves sometimes longer than the stems, the basal leaves reduced to nearly bladeless sheaths. Leaf blades 1–70 cm long, 3–8 mm wide, thick, light green, the margins minutely roughened or toothed, flat or somewhat folded. Leaf sheaths concave, the ligule somewhat wider than long and broadly V-shaped, the ventral side thin, papery, white or nearly so, and spotted or streaked with red, the lowermost sheath bases dark brown to nearly black. Inflorescences compound, with numerous spikes, these all similar and grouped into a large panicle with spicate branches, the lower branches conspicuous, to 4 cm long, the lowermost bracts hairlike, green, much shorter than the inflorescence, but sometimes about as long as the inflorescence branch, lacking a sheath. Spikes densely clustered along the branches, sessile, 3–7 mm long, 2–5 mm wide, inconspicuously staminate toward the tip and pistillate toward the base, oblong-elliptic to nearly circular in outline, with 9 to numerous densely spaced perigynia. Staminate scales 1.2–1.8 mm long, ovate, white with a green midrib. Pistillate scales 2.0–2.6 mm long, ovate, the tip pointed and sometimes short-awned, white with a green midrib. Perigynia 2.0–2.8 mm long, thick-walled, somewhat flattened, obtriangular to obovate in outline, very abruptly tapered to a short, flattened beak with minute teeth along the margins and 2 narrow teeth at the tip, the base angled to a very short stalk below the fruit, the sides rounded basally and angled toward the tip, mostly strongly several-nerved on the basal half of each surface, glabrous, dark brown to olive green or nearly black at maturity. Styles withering during fruit development, jointed to the main body of the fruit, which is not or minutely beaked at maturity. Stigmas 2. Fruits 1.0–1.4 mm long, elliptic to somewhat obovate in outline, biconvex and somewhat flattened in cross-section, reddish brown to brown. 2n=60, 64, 66. April–July.

Scattered in the eastern portion of the Ozark Division, and also known from a single historical locality in Dunklin County, in the Mississippi Lowlands (eastern U.S. west to Michigan and Arkansas, most common in the southeastern states). Emergent aquatics in sinkhole ponds, usually epiphytic on the bases of buttonbushes (Cephalanthus occidentalis, Rubiaceae).

This distinctive species is an indicator of high-quality sinkhole pond communities. It almost always occurs at the bases of buttonbushes, and the large clumps can form conspicuous, large tussocks or hummocks rooted on the submerged remains after a buttonbush dies. The combination of the paniculate inflorescence with well-developed lower branches and the dark-colored perigynia that are broadest near the tip make it easily recognized in the field.

Kolstad (1986) reported the occurrence of the related C. diandra Schrank in the state. Although this circumboreal species grows in both Nebraska and Illinois, to date no specimens have been located to voucher its existence in Missouri. Carex diandra differs from C. decomposita in its leaf sheaths, which are extended past the insertion point of the blade, and in its perigynia, which are lanceolate to ovate in outline and tapered gradually to a relatively long beak. Perhaps it will be found eventually in bottomland prairies or other wetlands in the northern half of the state.