Oak
Oak Mistletoe
Oak Ridge Lupine
Oakleaf Fleabane
Oakleaf Goosefoot
Oakleaf Hydrangea
Oat
Oatgrass
Obedient Plant
Oblongleaf Snakeherb
Obolaria
Ocala Blackberry
Ocala Vetch
Oceanblue Morning-glory
October Flower
Octopus Tree
Ogeechee Tupelo
Oil Palm
Okeechobee Gourd
Okenia
Okra
Old World Adderstongue
Old-man-in-the-spring
Oldenlandia
Oldfield Grass
Oldmaid
Oldwoman
Oleander
Oleaster
One-nerved Ernodea
Oneflower Bedstraw
Oneflower False Fiddleleaf
Oneflower Honeycombhead
Oneflower Vetch
Oneflowered Broomrape
Onefruit
Oneseed Bur Cucumber
Onesided Galenia
Onion
Openflower Rosette Grass
Opium Poppy
Oppositeleaf Spotflower
Orange Azalea
Orange Coneflower