• (1) O Ga Na Mu - Obovate Milkweed
• (2) Obovateleaf Sundew - Ohio 8243 Tomato Lycopersicon Lycopersicum
• (3) Ohio 8245 Tomato - Olallie Star Daylily
• (4) Olallie Summer Daylily - Oliva
• (5) Oliva - Oneside Wintergreen
• (6) Onesided Crinkleawn - Oobai Chijiku
• (7) Oochidome - Orange Bell Daffodil
• (8) Orange Bell-Lily - Oratorio Daffodil
• (9) Oratuomi - Orchid Cactus
• (10) Orchid Cactus - Orchid Cactus
• (11) Orchid Cactus - Oregon Drops of Gold
• (12) Oregon Eurhynchium Moss - Oriental Lily
• (13) Oriental Lily - Ornamental Oregano
• (14) Ornamental Oregano - Osha
• (15) Osha Colorado Cough-Root - Ostukhudus
• (16) Oswald Daffodil - Ovoid Spikerush
• (17) Ovsets Shellia - Ozzies Delight Daylily