Ranunculus pygmaeus (pygmy buttercup)

Colombia
Comandra umbellata ssp. pallida (pale bastard toadflax)
Commelina erecta (whitemouth dayflower)
Commelina erecta var. angustifolia (whitemouth dayflower)
Commelina virginica (Virginia dayflower)
Comoros
Congo, Democratic Republic of the
Congo, Republic of the
Conringia orientalis (hare's ear mustard)
Consolida ajacis (doubtful knight's-spur)
Consolida regalis
Convallaria majalis
Convolvulus arvensis
Convolvulus arvensis (field bindweed)
Conyza canadensis
Cook Islands
Cooperia drummondii (evening rainlily)
Coprinus alopecia
Coprinus atramentarius
Coprinus comatus
Coprinus comatus fo.ovatus
Coprinus ellisii
Coprinus lagopus
Coprinus megaspermus
Coprinus niveus
Coprinus picaceus
Coprinus plicatilis
Coprinus saccharinus
Coptis trifolia (threeleaf goldthread)

Image of Ranunculus pygmaeus (pygmy buttercup) 1
USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 2: 108.