1 Petals 10-18 mm long, 2-3× as long as the sepals; leaves 2-7 cm long; plants perennial, typically with some shoots not flowering.

..2 Leaf blades narrowly lanceolate to narrowly ovate, obtuse to acute at tip, more-or-less rounded at base; stems spreading or decumbent basally, ascending-erect distally.

....3 Leaf blades narrowly lanceolate, obtuse to acute, well-spaced on stem, moderately to densely pubescent with dull hairs but may be glabrate in age; plants forming small clumps

....3 Leaf blades narrowly ovate, obtuse and blunt at tip, tightly spaced on stem, very densely pubescent with silvery or translucent-white permanent hairs; plants form clumps to several dm wide; [endemic to serpentine in PA and MD]

..2 Leaf blades narrowly to broadly linear, acute or short-acuminate at tip, tapered to base; stems erect nearly whole length

......4 Nodes of the lower and middle stem lacking axillary leaf tufts; stems and leaf blades densely white-tomentose, obscuring the surfaces

......4 Nodes of the lower and middle stem with axillary tufts of leaves; stems and leaf blades villous, but thinly so and allowing the surface to be seen.

........5 Plants strongly rhizomatous with long-creeping shoots, lacking taproot; flowering stems usually 25-30 cm long; stem pubescence eglandular (glandular hairs present in the inflorescence only); sepals 5-7 mm long; anthers 1.0-1.1 mm long; petals often turning brown when dry; [alien]

........5 Plants clumped, with taproots or shortly rhizomatous; flowering stems usually 5-20 cm long; stem pubescence glandular; sepals 3.5-6 (-7) mm long; anthers 0.8-0.9 mm long; petals usually remaining white when dried; [native]

1 Petals 3-8 mm long, shorter than, equaling, or up to 1.5× as long as the sepals; leaves 0.5-3.0 cm long (to 8 cm long in C. nutans and C. brachypodum); plants annual, with all shoots producing flowers (except C. fontanum ssp. vulgare).

..........6 Perennial, matted at the base and rooting at the nodes.

............ 7 Sepals 5-7 mm long; petals 5-7 mm long; capsules cylindric, 9-13 mm long mm long

............ 7 Sepals 2.5-3 mm long; petals 2.5-3.5 mm long; capsules broadly ovoid, 4-5 mm long

..........6 Annual, taprooted.

............ ..8 Sepals with long, appressed, eglandular hairs extending beyond the tip of the sepal.

............ ....9 Inflorescence an open cyme, most of the pedicels longer than the sepals

............ ..8 Sepals lacking long, appressed, eglandular hairs.

............ ......10 Styles, sepals, and petals 3-4 (-5); capsule teeth 6-8 (-10).

............ ........11 Styles, sepals, and petals 4 (-5); capsule teeth 8 (-10); capsules ca. 1.5 × as long as the sepals; cauline leaves 2-3 × as long as wide

............ ........11 Styles, sepals, and petals 3 (-4); capsule teeth 6 (-8); capsules ca. 2 × as long as the sepals; cauline leaves 8-10 × as long as wide

............ ......10 Styles, sepals, and petals 5; capsule teeth 10.

............ ..........12 Bracts of the inflorescence with distinctly scarious margins; leaves mostly 0.5-1.0- (-1.5) cm long.

............ ............ 13 Petals equaling or surpassing the sepals; cleft in petal apex 1.0-1.5 mm deep

............ ............ 13 Petals shorter than the sepals; cleft in petal apex 0.2-0.5 (-0.9) mm deep

............ ..........12 Bracts of the inflorescence with green margins; leaves mostly (1.0-) 1.5-8 cm long.

............ ............ ..14 Pedicels 3-10 (-15) mm long; leaves to 3.5 cm long

............ ............ ..14 Pedicels (10-) 15-40 (-55) mm long; leaves to 8 cm long