• (1) O Ga Na Mu - Obsession Hosta
• (2) Obsession in Red Daylily - Oily Pili
• (3) Oily Pili - Old Man Weed
• (4) Old Man Whiskers - On And On Siberian Iris
• (5) On Broadway Daylily - Onion
• (6) Onion - Opuntia
• (7) Opuntia - Orazdıq
• (8) Orégano De Cartagena - Orchid Cactus
• (9) Orchid Cactus - Orchid Cactus
• (10) Orchid Cactus - Oregon Fleabane
• (11) Oregon Fleabane - Oriental Pea
• (12) Oriental Pea - Ornamental Pepper
• (13) Ornamental Pepper - Ostler's Mousetail
• (14) Ostler's Pepper-Grass - Ottawa Tomato
• (15) Otterbush - Oxtongue
• (16) Oxtongue - Կոտեմ