Ci
- Cicuta — water hemlocks
- Cicuta bulbifera — bulb-bearing water hemlock
- Cicuta maculata — spotted water hemlock, spotted cowbane, musquash-root, beaver-poison
- Cicuta virosa — MacKenzie's water hemlock, northern water hemlock
- Cimicifuga — cohoshes
- Cimicifuga racemosa — black cohosh, black snakeroot, black bugbane
- Cinna — wood reedgrasses
- Cinna arundinacea — stout wood reedgrass
- Cinna latifolia — slender wood reedgrass, drooping woodreed, broadleaf woodgrass
- Circaea — enchanter's nightshades
- Circaea alpina — dwarf enchanter's nightshade, small enchanter's nightshade
- Circaea lutetiana — Canada enchanter's nightshade, southern broadleaf enchanter's nightshade
- Cirsium — thistles
- Cirsium discolor — pasture thistle, field thistle
- Cirsium drummondii — Drummond's thistle, short-stem thistle, dwarf thistle
- Cirsium flodmanii — prairie thistle, woolly thistle, Flodman's thistle
- Cirsium hillii — Hill's thistle Threatened
- Cirsium muticum — swamp thistle, dunce nettle, horsetops
- Cirsium pitcheri — Pitcher's thistle, sand dune thistle
Read more about this topic: List Of Canadian Plants By Genus C