Cyperus resembles Kyllinga, but Cyperus has > 5 spikelet scales, whereas Kyllinga has 1-3 scales.

Sometimes classified as "Cyperus pedunculatus," Remirea maritima is a low, maritime species on beach dunes.

1. Plants with numerous (>30) inflorescence rays and no (or nearly no) bracts…C. prolifer (C. papyrus, another garden species, may have > 30 rays but is much larger to > 2 m tall vs. < 1 m tall.)

1. Plants otherwise…2

2. Stigmas 3; achenes 3-angled…6

2. Stigmas 2; achenes 2-angled…3

Species with 2 styles and flattened achenes:

3. Spikelets crowded densely into cylindric spikes…C. alopecuroides (a large invasive exotic species)

3. Spikes not densely crowded (rachis visible between the spikelets, or if the rachis not visible, the plant then with a total of < 100 spikelets vs. too many to count in C. alopecuroides)…4

4. Scales awned, the margins white…C. pumilus

4. Scales not awned (may have a tiny cusp), the margins not white…5

5. Achene much longer than wide; spikelets 1.3-1.6(2) mm wide…C. polystachyos (very common weed and highly variable, the spikelets variable in length)

5. Achene ellipsoid or ovate, covered with square cells; spikelets > 2 mm wide…C. lanceolatus

Species with 3 styles and triangular achenes:

6. Culm scabrous…C. surinamensis (C. distinctus has similar appearance but smooth stems and achenes with white spongy bases)

6. Culm smooth…7

7. Stems hollow, to 2 m tall; spikelets 5 cm long; bract appearing the be an extension of the culm making the spikelets appear to be lateral (then resembling Schoenoplectus, which differs by having > 1 achene per much-shorter spikelet), or the spikelets in an umbellate arrangement at the top of the culm; leaves and culms septate…C. articulatus (Rare)

7. Plants otherwise…8

8. Plants < 1 m tall, 3-6 loosely cylindrical spikes, 10-60 spikelets 5-8 mm long...C. tetragonus

8. Plant otherwise...9

9. Plants > 1 m tall, having > 40 rays, the culm > 1.5 cm in diameter…C. papyrus (Papyrus, an escaped horticultural species)

9. Plants not with the above combination of characters…10

10. Plants with >17 broad flat bracts (these often sticking straight out horizontally or nearly so)…C. involucratus (Umbrella Sedge, an escaped horticultural species)

10. Plants otherwise…11

11. Achenes with spongy white base…C. distinctus (looks like S. surinamensis but with smooth stem and with the characteristic white achene base)

11. Achenes without white spongy base…12

12. Spikelets in elongate cylindric spikes, the rachis breaking apart and having the segments remaining with the achenes….C. odoratus (A large common eye-catching species of stagnant ditches and shores. Similar, C. strigosus has spikes with a bottlebrush appearance resembling C. odoratus, but C. odoratus has round vs. flat spikelets 0.8-1.9 vs. 0.6-0.8 mm wide.)

12. Rachis not cylindric, not with corky wings, not breaking apart with the achenes…13

13. Spikelets in dense heads (with distinct globose or cylindric shape)…14 (Note: If plant has a single sessile head > 3 cm diam. made of numerous long spikelets, consider anomalous specimen of C. planifolius, a seashore species appearing below)

13. Spikelets loosely arranged (the rachis showing between the bases, or the bases crowded or touching but the clusters irregular in outline)…18

14. Spikelet clusters globose…C. croceus

14. Spikelet clusters cylindric…15

15. Spikelets 2.2-4 mm long; leaves 1.5-4 mm wide…C. ovatus (spikelets remain greenish, species of dry sandy habitats)

15. Spikelets >3-30 mm long (if spikelets < 4 mm the leaves > 5 mm wide)…16

16. Leaves 1-4 mm wide…C. strigosus (Spikes with a bottlebrush appearance resembling C. odoratus but C. odoratus with a round vs. flat spikelet 0.8-1.9 vs. 0.6-0.8 mm wide) (C. rotundus has tubers and similarly narrow leaves but reddish spikelets only rarely exceeding 4 mm long vs. usually well over 5 mm long)

16. Leaves 5-13 mm wide…17

17. Spikelets 3-7 mm long; spikes usually < 1.5 cm in diameter.…C. ligularis (Spikelets becoming brownish vs. remaining green in C. ovatus)

17. Spikelets 6-22 mm long; spikes > 1.5 cm in diameter.…C. planifolius (Achene 1.3-2 mm)

18. Inflorescences vaguely paniculate with the second-order branches having a feathery-shaggy appearance covered for most of their length with loosely arranged spikelets…C. iria

18. Not as above…19

19. Spikelets red or with reddish markings…20

19. Spikelets green or yellowish…21

20. Scales white with two red spots…C. sphacelatus

20. Scales reddish throughout (except for margins and midrib)…C. rotundus (This and C. esculentus are our only two tuber-producing species. Both are common aggressive weeds)

21. Leaf bladeless (sheath only)…C. haspan (Stem strongly triangular. Spikelets 1-1.6 mm wide)

21. Plants with leaf blades…22

22. Rachis long, visible between the spikelets, these spaced out along the rachis…23

22. Rachis short, not visible, the spikelets crowded basally in digitate arrangement…24

23. Plants stoloniferous with tubers (see also C. rotundus); spikelets (1.2)1.4-2(3) mm wide…C. esculentus (Scales mostly brown or yellow-brown)

23. Plants with erect rhizome, having possible radiating stolons but no tubers; spikelets 0.6-0.8 mm wide…C. strigosus (Spikes with a bottlebrush appearance resembling C. odoratus but C. odoratus with a round vs. flat spikelet 0.8-1.9 vs. 0.6-0.8 mm wide)

24. Plants rhizomatous; spikelets per cluster (1)2-4(6)…C. lecontei

24. Plants cespitose; spikelets per cluster usually 3-20…C. compressus