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Key to Cerastium

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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; [exotic]
        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
             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
                 9 Inflorescence a compact, cymose cluster, most of the pedicels shorter 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.
image of plant
Show caption*© Brian Finzel, some rights reserved (CC BY-SA), uploaded by Brian Finzel
                       12 Bracts of the inflorescence with distinctly scarious margins; leaves mostly 0.5-1.0- (-1.5) cm long.
image of plant
Show caption*© Brian Finzel, some rights reserved (CC BY-SA), uploaded by Brian Finzel
                          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