1. Pls annual, gen wider than tall, rounded to cushion-like; taproot red, purple when dry (often staining herbarium paper); flower bracts present
    2. Calyx basally tubular, tube circumscissile in fr ............................................................................................................................ C. circumscissa
    2' Calyx of distinct sepals, intact in fr .................................................................................................................................................. C. micrantha
1' Pls annual or perennial, gen taller than wide; taproot usually not red, or purple when dry; flower bracts absent or present
    3. All nutlets of fruit with a smooth, shiny dorsal surface
        4. Sepal trichomes hooked, recurved .................................................................................................................................................. C. flaccida
        4' Sepal trichomes straight
            5. Nutlet groove strongly off-center, curved parallel to nearest margin .............................................................................................. C. affinis
            5' Nutlet groove central, straight
                6. Sepals 6-10 mm in fr; longest sepal bristles 3-4 mm in fr ........................................................................................................ C. ganderi
                6' Sepals 1-6 mm in fr; longest sepal bristles < 3 mm in fr
                    7. Flower bracts present ..................................................................................................................................................... * C. maritima
                    7' Flower bracts absent
                        8. Sepals 1.5–2.5 mm in fl, 3-6 mm in fr; style ca. 2/3 length of nutlet .......................................................................... C. clevelandii
                        8' Sepals ≤ 1 mm in fl, 1-2 mm in fr; style < half nutlet length ................................................................................... C. microstachys
    3' At least one nutlet of fruit roughened: ridged, papillate (very tiny bumps), tuberculate (prominent, moderately sized bumps),
            and/or muricate (enlarged, radially elongate bumps)
        9. Nutlet margin sharp-angled and flattened into a narrow rim to a broad wing
            10. Pedicels 1-4 mm long in fr; pl annual or perennial
                  11. Nutlets of fruit similar, dorsally papillate-tuberculate, margin with narrow, flattened rim or wing; pl usu. annual,
                        with major central axis; infl. in fr dense ............................................................................................................................ C. holoptera
                  11' Nutlets of fruit unequal, 1 longer & dorsally papillate to papillate-tuberculate, 2-3 shorter & dorsally papillate-tuberculate,
                        margins with very narrow, flattened rim; pl per (but may fl first year), without major, central axis; infl. in fr open ......... C. racemosa
            10' Pedicels < 1 mm long in fr; pl annual
                    12. Nutlets of fruit similar, margin narrowly winged, dorsal surface finely papillate; fls bracteate (bracts deciduous) ............. C. costata
                    12' Nutlets of fruit similar or of two kinds, 3-4 nutlets prominently or narrowly winged, wing gen lobed at tip,
                          1 nutlet sometimes not winged, dorsal surface of all tuberculate; fls ebracteate ............................................................ C. pterocarya
        9' Nutlet margin rounded, ridged, or sharp-angled (acute to obtuse), but not flattened as a rim or wing
            13. Nutlets heteromorphic in size, one nutlet larger than the other(s)
                  14. Nutlets 4 per fruit, all similar in sculpturing, papillate ................................................................................................... C. angustifolia
                  14' Nutlets 1-4 per fruit, the larger nutlet smooth, the other(s) smaller and papillate to tuberculate
                        15. Fl bracts absent; calyx in fr sub-globose, sepals 1-1.5 mm long; nutlets 4 per fr, < 1 mm long, triangular–ovate ... C. micromeres
                        15' Fl bracts present, calyx in fr oblong, sepals 2-3 mm long; nutlets 1-2 per fruit, 1.5-2 mm long, oblong-lanceolate .. * C. maritima
            13' Nutlets homomorphic in size and sculpturing
                  16. Sepals 3-6 mm long in fl, 5-10 mm long in fr
                        17. Stems with appressed trichomes; nutlets lanceolate, long-acuminate ....................................................................... C. nevadensis
                        17' Stems with appressed and spreading trichomes; nutlets lance-ovate, narrowly acute to slightly acuminate ............... C. barbigera
                  16' Sepals 1-3 mm long in fl, 2-5 (rarely 6) mm long in fr
                        18. Nutlets 1-2 per fruit, lanceolate
                             19. Fr sepals ovate-elliptic, nutlets narrowly acute, margin sharp-angled to ridged, dorsal tubercles often spinulose . C. utahensis
                             19' Fr sepals linear-oblong, nutlets acuminate, margin rounded, dorsal tubercles not obviously spinulose ................. C. decipiens
                        18' Nutlets usually 4 per fruit, lance-ovate to ovate
                              20. Corolla 1-2 mm wide (lobe to lobe), nutlet dorsal face flattened to low-convex,
                                    finely papillate and tuberculate .............................................................................................................................. C. simulans
                              20' Corolla 1-8 mm wide (lobe to lobe), nutlet dorsal face convex, coarsely tuberculate to muricate
                                    21. Corolla 3-8 mm wide (lobe to lobe); nutlets lance-ovate, coarsely tuberculate, without dorsal ridge ........... C. intermedia
                                    21' Corolla 1-8 mm wide (lobe to lobe); nutlets ovate to deltate, muricate, with (± obscure) dorsal ridge ............ C. muricata