| Common Name | Latin Name |
|---|---|
| Calamint | Calamintha nepeta |
| Calepina | Calepina irregularis |
| Caltrop | see Puncturevine |
| Canada Onion | see Wild Onion |
| Canada Thistle | Cirsium arvense |
| Canadian Garlic | see Wild Onion |
| Cancer weed | see Lyreleaf Sage |
| Cancer-root | see Squaw-root |
| Caper Spurge | Euphorbia lathyris |
| Carolina False Dandelion | Pyrrhopappus carolinianus |
| Carolina Foxtail | Alopecurus carolinianus |
| Carolina Geranium | Geranium carolinianum |
| Carpet Bentgrass | see Creeping Bentgrass |
| Carpet Bugle | see Bugleweed |
| Carpetweed | Mollugo verticillata |
| Castor Bean | Ricinus communis |
| Castor Oil Plant | see Castor Bean |
| Cat'S Clover | see Birdsfoot Trefoil |
| Cat's claw | see Sensitive Brier |
| Catbrier | see Bristly Greenbrier |
| Catbrier | see Greenbrier |
| Catmint | see Catnip |
| Catnip | Nepeta cataria |
| Cattails | Nympha spp. |
| Catwort | see Catnip |
| Celery-Leaf Buttercup | see Crowfoot Buttercup |
| Chara | Chara spp. |
| Cheat | Bromus secalinus |
| Chicory | Cichorium intybus |
| Chinese Fountain Grass | Pennisetum alopecuroides |
| Chinese Lantern | see Apple-of-Peru |
| Chinese Yam | Dioscorea batatas |
| Cinnamon Vine | see Chinese Yam |
| Clammy Groundcherry | Physallis heterophylla |
| Clasping Milkweed | Asclepias amplexicaule |
| Cleavers | see Bedstraw |
| Climbing False Buckwheat | Polygonum scandens |
| Climbing Rose | see Prairie Rose |
| Cockspur Thorn | Crataegus crus-galli |
| Coco | see Purple Nutsedge |
| Coffee Senna | Cassia occidentalis |
| Common Balm | see Bee-balm |
| Common Beggar-ticks | Bidens frondosa |
| Common Beggarticks | see Common Beggar-ticks |
| Common Blackberry | see Smooth Blackberry |
| Common Blue Violet | Viola papilionacea |
| Common Bugleweed | see Bugleweed |
| Common Burdock | Arctium minus |
| Common Buttonweed | see Poorjoe |
| Common Catsear | Hypochoeris radicata |
| Common Chickweed | Stellaria media |
| Common Cocklebur | Xanthium strumarium |
| Common Dayflower | see Asiatic Dayflower |
| Common Dewberry | see Northern Dewberry |
| Common Duckweeds | see Duckweeds |
| Common Eveningprimrose | Oenothera biennis |
| Common Greenbrier | see Roundleaf Greenbrier |
| Common Groundsel | Senecio vulgaris |
| Common Hop Sedge | see Hop Sedge |
| Common Lambsquarters | Chenopodium album |
| Common Lespedeza | Lespedeza striata |
| Common Mallow | Malva neglecta |
| Common Milkweed | Asclepias syriaca |
| Common Mullein | Verbascum thapsus |
| Common Pokeweed | Phytolacca americana |
| Common Purslane | Portulaca oleracea |
| Common Ragweed | Ambrosia artemisiifolia |
| Common Reed | Phragmites australis |
| Common Saint Johnswort | see Saint Johnswort |
| Common Sunflower | Helianthus annuus |
| Common Tansy | Tanacetum vulgare |
| Common Teasel | Dipsacus fullonum |
| Common Toadflax | Linaria canadensis |
| Common Unicorn Plant | see Devil's Claw |
| Common Venus Looking-glass | Triodanis perfoliata |
| Common Vetch | Vicia sativa |
| Common Waterhemp | Amaranthus tuberculatus |
| Common Yarrow | Achillea millefolium |
| Compass Plant | Silphium laciniatum |
| Coontail | Ceratophyllum demersum |
| Coralberry | see Buckbrush |
| Coreopsis Beggarticks | Bidens polylepis |
| Corn Buttercup | Ranunculus arvensis |
| Corn Campion | see Corn Cockle |
| Corn Cockle | Agrostemma githago |
| Corn Gromwell | Buglossoides arvensis |
| Corn Rose | see Corn Cockle |
| Corn Speedwell | Veronica arvensis |
| Corn Spurry | Spergula arvensis |
| Cornflower | Centaurea cyanus |
| Cornsalad | Valerianella radiata |
| Cotton Morningglory | Ipomoea cordatotriloba |
| Cotton thistle | see Scotch Thistle |
| Cottonwood | Populus deltoides |
| Cow-itch | see Trumpetcreeper |
| Creamy Wild Indigo | Baptisia leucophaea |
| Creeping Bentgrass | Agrostis palustris |
| Creeping Phlox | Phlox subulata |
| Creeping Red Woodsorrel | Oxalis corniculata |
| Creeping Rush | Juncus repens |
| Creeping Water Purslane | see Water Purslane |
| Creeping Woodsorrel | see Creeping Red Woodsorrel |
| Creeping charlie | see Ground Ivy |
| Cressleaf Groundsel | Senecio glabellus |
| Crested anoda | see Spurred Anoda |
| Crimson Fountain Grass | see Chinese Fountain Grass |
| Crossvine | Bignonia capreolata |
| Crow Toes | see Birdsfoot Trefoil |
| Crowfoot Buttercup | Ranunculus sceleratus |
| Crowfoot violet | see Birds Foot Violet |
| Crowfootgrass | Dactyloctenium aegyptium |
| Crownvetch | Coronilla varia |
| Cup Plant | Silphium perfoliatum |
| Curly Dock | Rumex crispus |
| Curlycup Gumweed | Grindelia squarrosa |
| Curlyleaf Pondweed | Potamogeton crispus |
| Cursed Buttercup | see Crowfoot Buttercup |
| Cursed Crowfoot | see Crowfoot Buttercup |
| Cutleaf Eveningprimrose | Oenothera laciniata |
| Cutleaf Geranium | Geranium dissectum |
| Cutleaf Teasel | Dipsacus laciniatus |
| Cypress Spurge | Euphorbia cyparissias |
| Cypressvine Morningglory | Ipomoea quamoclit |
| Cypressweed | see Dogfennel |
