- Caducous
- Caespitose
- Calceolate
- Callose
- Callus
- Calyculus
- Campanulate
- Canaliculate
- Capitate
- Capitulum
- Capsule
- Carinate
- Carnose
- Carpel
- Cartilaginous
- Cataphyll
- Catch-root
- Caudate
- Caudicle
- Caulescent
- Cauline
- Character state
- Cilia
- Ciliate
- Cirrhose
- Clade
- Cladogenesis
- Cladogram
- Clavate
- Claw
- Cleistogamous
- Clinandrium
- Cochleate
- Coherent
- Column
- Column arm
- Column foot
- Column wing
- Compressed
- Condensed
- Congeneric
- Conical
- Connate
- Connective
- Conspecific
- Contorted
- Convergent evolution
- Convolute
- cool growing
- Cordate
- Coriaceous
- Corm
- Cortex
- Corymb
- Crenate
- Crenulate
- Crisped
- Cristate
- Cucullate
- Cuneate
- Cuniculus
- Cuspidate
- Cylindrical
- Cymbiform
- Cystoliths