- Cacti
- Cactus, Beavertail
- Cactus, Blue Barrel
- Cactus, Candy
- Cactua, Compass Barrel
- Cactus, Cottontop Barrel
- Cactus, Fire Barrel
- Cactus, Fishhook Barrel
- Cactus, Golden Barrel
- Cactus, Purple Pancake
- Calendula
- California Fan Palm
- California Incense Cedar
- California Palm
- California Pepper
- Canary Island Palm
- Canary Island Pine
- Candy Cactus
- Candytuft, Wild
- Canna Lily
- Canyon Grape
- Canyon Palm
- Cardinal Flowers
- Carnation
- Carpet Bugle Ajuga
- Cassia, Desert
- Cassia, Feathery
- Cassia Shrubby
- Cassia, Silver-leaf
- Cassia, Silvery
- Cat Thyme
- Cat's Claw Vine
- Catalpa, Northern
- Catalpa, Western
- Catclaw Acacia
- Cedar, Blue Atlas
- Cedar, California Incense
- Cedar, Deodora
- Cedar, Incense
- Cedar, Weeping Alaska
- Cenizo
- Centennial Broom
- Centennial Coyote Bush
- Century Plant
- Chamisias
- Chaparral Bush
- Chaste Tree
- Cherry, Western Sand
- Chestnut, Horse
- Chestnut, Red
- Chihuahuan Sage
- Chinese, Elm
- Chinese, Evergreen Elm
- Chinese, Jasmine
- Chinese, Wisteria
- Chocolate Flower
- Chokecherry
- Cholla, Teddy Bear
- Cholla, Silver
- Cholla, Staghorn
- Chrysanthemum
- Conquefoil, Shrubby
- Claret Cup Cactus
 Clematis
- Cliff Fendlerbush
- Cliff Spirea
- Cliffrose
- Climbing Fig
- Climbing Rose
- Coleus
- Colorado Blue Spruce
- Colorado Spruce
- Columbines
- Common Hackberry
- Common Thrift
- Common Trumpet Creeper
- Common Wormwood
- Compass Barrel Cactus
- Coneflowers
- Confederate Vine
- Coral Bells
- Coral Vine
- Coralberry
- Coreopsis
- Corkbark Fir
- Cornus mas
- Cosmos
- Contoneaster
- Pyrenees
- Red Clusterberry
- Rock
- Rockspray
- Cottage Pink
- Cottontop Barrel Cactus
- Cow's Tongue
- Coyote Bush
- Crabapple
- Crabapple, Siberian
- Cranesbill
- Creeper, Common Trumpet
- Creeper
- Creosote Bush
- Crested Tongue Penstemon
- Crimson Pygmy Japoanese Barberry
- Crocus
- Currant
- Currant, Alpine
- Currant, Golden
- Currant, Indian
- Curved Yucca
- Cut Leaf Birch
- Cut Leaf Dusty Miller
- Cypress
- Cypress, Boulevard
- Cypress, False
- Cypress, Hinoki
- Cypress, Lawson's
- Cypress, Sawara
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