Cyperus section Tetragoni

Tucker, Gordon C. & Verloove, Filip, 2018, A new species of Cyperus sect. Tetragoni (Cyperaceae) from Colombia, South America, Phytotaxa 362 (3), pp. 287-291 : 290

Key to the species of Cyperus section Tetragoni in Central and South America

1. Inflorescence with rays mostly terminated by single spikes; spikes ovoid- to oblong-cylindric, rather lax; scales laterally reddish or reddish-brown...............................................................................................................................................................................2.

- Inflorescence with rays terminated by 1–6 spikes (terminal spike longer or larger than the rest); spikes typically rather dense, cylindric to oblong-cylindric; scales laterally stramineous, greenish, off-white, or brownish.............................................................4.

2. Scales laterally reddish; anthers 2–2.3 mm; achenes 2–2.8 mm; eastern Brazil................................................ Cyperus diamantinus

- Scales laterally reddish-brown; anthers 0.6–0.8 mm; achenes 1.5–2.1 mm; southern U.S. to Ecuador...........................................3.

3. Rachis with 24–28 spikelets per cm (rarely less); scales appressed, (2.6–) 2.8–3.2 (–3.4) mm long................. Cyperus thyrsiflorus .

- Rachis with about 15 spikelets per cm; scales spreading, about 2.2 mm long ............................................................ Cyperus bernalii

4. Scales laterally densely red-speckled, with mucronate apex 0.2–0.6 mm long ................................................. Cyperus lentiginosus

- Scales laterally without red speckles, entire or with mucro at most 0.2 mm long............................................................................5.

5. Leaves coriaceous, septate-nodulose, margins strongly revolute, apex long, attenuate, narrow .......................... Cyperus coriifolius

- Leaves herbaceous, flat or inversely W-shaped, hardly septate nodulose, apex shortly acuminate..................................................6.

6. Spikes broadest at base; spikelets linear-lanceolate; scales elliptic; achene oblong-ellipsoid .................... Cyperus hermaphroditus .

- Spikes of equal width at base; spikelets subulate; scales oblong-elliptic; achene oblong................................................................7.

7. Rays decidedly unequal in length; spikes narrowly cylindric (2–3 times longer than wide); spikelets diverging at right angle; Central America ...................................................................................................................................................... Cyperus tribrachiatus

- Rays equal or subequal (at least the three longest ones); spikes oblong-cylindric (about as long as wide); spikelets typically spreading obliquely; Venezuela; eastern Brazil to northern Argentina......................................................................... Cyperus meyenianus