23. Cyperus retrofractus (L.) Torr.

Pl. 72 i, j; Map 267

C. dipsaciformis Fernald

Plants perennial with short, knotty rhizomes, lacking tubers. Aerial stems 30–90 cm long, sharply trigonous, strongly roughened, at least toward the tip. Leaf blades 15–60 cm long, 3–8 mm wide (sometimes with the margins inrolled and thus appearing narrower), shorter than to about as long as the stems. Inflorescences irregular umbels with 1–3 sessile spikes and 4–13 rays, each ray smooth or at most slightly roughened near the tip, ending in a spike. Inflorescence bracts 3–12, shorter than to longer than the rays, mostly spreading to ascending. Spikes 15–35 mm long, with 30 to over 100 spikelets, obovoid to narrowly obovoid, relatively dense, the spikelets mostly strongly reflexed, attached immediately adjacent to one another on the axis, the spikelet bases sometimes densely overlapping such that basal portions are not visible when fresh (pressed specimens become distorted). Spikelets 6–14 mm long, narrowly linear, sharply pointed and sometimes somewhat bent at the tip, circular to somewhat 4-angled in cross-section, with 3–6 scales and 2–4 fertile florets, jointed to the axis of the spike and usually shed as an intact unit. Spikelet axis winged. Spikelet scales 4.0–5.5 mm long, strongly overlapping, broadly lanceolate, bluntly angled along the back, sharply pointed at the tip, straight to slightly incurved with an appressed tip, with 9–11 nerves, straw-colored to yellowish brown, sometimes tinged with reddish purple, the midrib green. Stamens 3, the anthers 0.7–1.2 mm long. Stigmas 3. Fruits 2.5–3.0 mm long, narrowly oblong in outline, sharply 3-angled in cross-section, the sides flat, the surface finely pebbled, brown to dark brown, shiny. July–October.

Scattered in the Mississippi Lowlands, including Crowley’s Ridge, west locally to Oregon County (Pennsylvania to Georgia west to Missouri and Arkansas). Sand prairies, openings of dry upland forests on sand, acid seeps, and cherty creek banks; also roadsides, fallow, sandy fields, and disturbed, dry, sandy areas.

In the older botanical literature (e.g., Gleason and Cronquist, 1963), there was sometimes confusion as to the correct application of names in this complex, with plants now treated as C. plukenetii placed under the name C. retrofractus var. retrofractus and true C. retrofractus restricted to C. retrofractus var. dipsaciformis. Carter (1984) and Carter and Jarvis (1986) showed that both of these names refer to the same taxon, which is a different species than C. plukenetii.

Although most of the Missouri collections of C. retrofractus have totally smooth inflorescence branches, a few specimens are somewhat roughened near the tips of the rays and might therefore be mistakenly determined as C. plukenetii. However, in other respects these specimens are typical of C. retrofractus and hybridization between the two taxa has not been documented (Carter and Jarvis, 1984). In addition to the differences in spikelet length, floret number, and inflorescence branch roughening included in the key above, C. retrofractus also has stems that are much more sharply trigonous than are those of C. plukenetii and tends to have longer, less densely flowered spikes and longer inflorescence bracts.