UMass Extension Weed Herbarium
| Common Name | Scientific Name | Family Name | |
|---|---|---|---|
| cocklebur | Xanthium strumarium | Asteraceae (Compositae) - Aster or Sunflower Family | |
| cockspur grass | see - barnyardgrass | ||
| coltsfoot | Tussilago farfara | Asteraceae (Compositae) - Aster or Sunflower Family | |
| compass plant | see - lettuce, prickly | ||
| compass weed | see - lettuce, prickly | ||
| copper-leaf, rhombic | Acalypha rhomboidea | Euphorbiaceae - Spurge Family | |
| cottonweed | Froelichia gracilis | Amaranthaceae - Amaranth Family | |
| couchgrass | see - quackgrass | ||
| cow parsnip | Heracleum lanatum | Apiaceae (Umbelliferae) - Carrot Family | |
| cowbane | see - water hemlock, spotted | ||
| cowcress | see - pepperweed, field | ||
| crabgrass, hairy | see - crabgrass, large | ||
| crabgrass, large | Digitaria sanguinalis | Poaceae (Graminae) - Grass Family | |
| crabgrass, silver | see - goose grass | ||
| crabgrass, small | see - crabgrass, smooth | ||
| crabgrass, smooth | Digitaria ischaemum | Poaceae (Graminae) - Grass Family | |
| cranesbill, spotted | see - geranium, wild | ||
| creeping Charlie | see - ivy, ground | ||
| creeping Jenny | see - moneywort | ||
| cress, mouse-ear | Arabidopsis thaliana | Brassicaceae (Cruciferae) - Mustard Family | |
| cress, winter | see - rocket, yellow | ||
| crowfoot | see - goose grass | ||
| crowfoot | see - buttercup, smallflower | ||
| crowfoot, kidney-leaved | see - buttercup, smallflower | ||
| crowfoot, smooth-leaved | see - buttercup, smallflower | ||
| crowfoot, tall | see - buttercup, tall | ||
| crown vetch, trailing | Coronilla varia | Fabaceae (Leguminosae) - Pea or Bean Family | |
| cuckooflower | see - bittercress, cuckoo | ||
| cuckooflower | see - ragged robin | ||
| cucumber, wild | Echinocystis lobata | Cucurbitaceae - Gourd Family | |
| cup plant | Silphium perfoliatum | Asteraceae (Compositae) - Aster or Sunflower Family | |
| cypress, mock | see - kochia | ||
| cypress, summer | see - kochia |