O
- OAK TREE
- OBEDIENT PLANT, FALSE DRAGONHEAD
- OCONEE BELLS
- OKRA
- OLEANDER
- OLIVE
- ONCIDIUM
- ONION
- OPHIOPOGON
- OPUNTIA
- ORANGE JESSAMINE
- ORCHID CACTUS
- ORCHID TREE
- ORCHID VINE
- OREGANO, MARJORAM
- ORNAMENTAL POMEGRANATE
- ORNAMENTAL ALLIUM
- ORNITHOGALUM
- ORTHOSIPHON
- OSAGE ORANGE, BOIS D’ARC
- OSMANTHUS
- OSMUNDA
- OSTRICH FERN
- OXALIS
- OXBLOOD LILY