1 | Inflorescence a single terminal globose or semiglobose head. Stems leafy only towards the base. Lowest flower ♀ (exceptionally in R. rubra with a single stamen), upper one(s) ♂. Involucral bracts sheathless. |
1' | Inflorescence paniculate or consisting of 2-6 dense globose heads, in the latter case racemiform or spiciform. Stems leafy throughout. Lowest flower bisexual, the upper one(s) ♂ or ♀ |
2 | Nut laterally compressed (its edge towards the axis of the spikelet), turgidly biconvex, obovate or broadly obovate. Bristles sometimes as long as the nut, usually distinctly shorter, sometimes obsolete. Infructes- cence globose, brown. Stamens usually 3. Leaves and longest bracts almost keeled by the strong midrib. |
2' | Nut strongly dorsiventrally compressed (its face towards the axis of the spikelet), with concave to slightly convex sides, oblong-obovate to oblong. Bristles at least partly distinctly longer than the nut. Inflorescence usually semiglobose, pale brown. Stamens usually (1-)2. Midrib of leaves and bracts not prominent. |
3 | Nut usually with obtuse edges. |
3' | Nut with sharp edges. |
4 | Spikelets linear-lanceolate, 11-14 mm long. Bristles much exceeding the top of the style-base, the outer 3 densely long-plumose at the base, the longest (8-)11-12 mm long. Style-base about as broad as the nut. |
4' | Spikelets lanceolate, (6-)8-10mm long. Bristles about reaching the top of the style-base, at most slightly exceeding it, with glabrous or ciliate base, the longest 6-8 mm long. Style-base much narrower (about ½ as wide) as the nut |
5 | Nut very small, obovate, 1½-1¾ mm long, shining brown when ripe, hispidulous at the top only. Longest bristles 3-4 times as long as the nut. Style-base distinctly constricted at the base, not decurrent on the shoulders of the nut |
5' | Nut oblong-obovate, 2-2¾(-3) mm long, blackish brown when ripe, papillose or setulose all over, sometimes almost glabrous. Longest bristles slightly longer than to about twice as long as the nut, rarely longer. Style-base not or hardly constricted at the base, often slightly decurrent on the shoulders of the nut. |
6 | Nut papillose-tuberculate. Nut-bearing (5th) glume distinctly longer (c. 2 mm) than the next lower one. Ripe spikelets somewhat gaping, the bristles exserted (hence visible from the outside). Upper flower with 2(-3) stamens and 0-4 bristles. Very slender, with leaves 1-2 mm wide and stems ½-1 mm thick |
6' | Nut setulose to almost glabrous. Nut-bearing glume about as long as the next lower one. Spikelets not gaping at maturity, the bristles completely hidden by the glumes. Upper flower with 1-2 stamens, without bristles. Less slender, with leaves up to 4 mm wide and stems 1-2 mm thick. |
7 | Inflorescence consisting of 2-6 dense globose heads, with stellately spreading spikelets, one head to each primary sheathless bract. Spikelets 1-flowered. Bristles capillary, flexuous, smooth or almost so. |
7' | Inflorescence paniculate, consisting of 1-4 superposed corymbiform anthelas each subtended by a long- sheathing bract. Spikelets 2 several-flowered. Bristles rigid, straight, scabrous, or absent. |
8 | Apex of the nut suddenly narrowed ir’o a distinct neck. Nut 3½-5 mm long, smooth. |
8' | Apex of the nut obtuse or truncate, without neck. Nut 1¼-4 mm long, transversely wavy-ridged or irregularly plicate-rugose. |
9 | Bristles present. Style-base compressed-conical to almost subulate, from slightly broader than long to much longer than broad. Leaves flat or canaliculate, not setaceous. |
9' | Bristles absent. Style-base saddle-shaped, i.e. much depressed and much broader than high. Nut 1¼-1½ mm long, coarsely transversely wrinkled. Leaves setaceous. |
10 | Stems slender. Leaves 2-3(-5) mm wide, the sheaths of the cauline ones truncate at the orifice (without appendage). Spikelets with 2-4 ♀ flowers (upper ones often tabescent). Style-base ½ as long to as long as the nut. Glumes spirally arranged. Style deeply bifid. Nut 1½-2 mm long, finely transversely wrinkled |
10' | Stems rather stout to stout. Leaves (3-)4-20 mm wide, the sheaths of the cauline ones at the orifice with a membranous appendage opposite the blade. Only the lowest flower ♀. Style-base longer than the nut. Glumes distichous or almost so. Style shortly bilobed. Nut 2½-4 mm long. |
11 | Style-base about as wide as the nut, deeply grooved on both sides. Nut irregularly plicate-rugose. Leaves 8-20 mm wide |
11' | Style-base much narrower than the nut, almost subulate, not grooved. Nut regularly transversely wrinkled. Leaves 4-6 mm wide |