Oak: arexene Oak: arkansana
Oak: brantii Oak: candicans
Oak: castaneifolia Oak: chrysolepis, Live
Oak: emoryi, Live Oak: falcata, Spanish
Oak: hemisphaerica, Laurel Oak: infectoria
Oak: infectoria veneris Oak: ithaburensis, Vallonea
Oak: macrocarpa, Burr Oak: macrocarpa, Mossy Cup
Oak: macroroburhybrid Oak: marilandica, Blackjack
Oak: quadrangulata Oak: rugosa, Netleaf
Oak: salicina Oak: schuetteihybrid
Oak: texana, Spanish Oak: turnerihybrid
Oak: velutina, Black Oakleaf Mountain Ash
Ochrosia Ocotillo: purpusii
Octopus Plant: actinophylla (spp.) Octopus Plant: actinophylla 'Amate™'
Octopus Tree (spp.) Octopus Tree 'Amate™'
Ogeechee Lime Ogeechee Tupelo
'Ogi nagare' Japanese Maple Ohio Buckeye (spp.)
Ohio Buckeye 'Monticola' Ohio Buckeye 'Sargentii'
Ohio Buckeye: glabra pallida 'Ohlendorfii' Norway Spruce
Oil Tree, Poonga 'Ojochin' Oriental Cherry
'Okima' Japanese Maple 'Oklahoma' Oklahoma Redbud
Oklahoma Redbud 'Oklahoma' Oklahoma Redbud 'Texas White'
'Okukuji nishiki' Japanese Maple 'Okushimo' Japanese Maple
'Old Gold' American Holly Old Man Banksia
Old Man Palm Old Man's Beard
Old Man's Beard: virginicus 'Oldhamiana' Norway Spruce
Oleander, Mexican Oleander, Yellow
Oleaster: angustifolia Olifants River Euphorbia
Olive Olive Holly (spp.)
Olive, Fortune's Sweet Olive, Fragrant (spp.)
Olive, Holly Tea (spp.) Olive, Madagascar
Olive, Russian Olive, Sweet (spp.)
Olive, Tea (spp.) Olive, Texas Wild
Olive, Wild Olive: americanus, Wild
Oliver's Maple 'Olmsted' Norway Maple
'Olympia' Chinese Juniper 'Olympic' Littleleaf Linden
Ombu Omeo Grevillea
Orange Berry Pittosporum (spp.) 'Orange Dream' Japanese Maple
Orange Jasmine Orange Thorn
Orange Thorn: spinescens Orange Wattle
Orange, Bitter (spp.) Orange, Hardy (spp.)
Orange, Japanese Hardy (spp.) Orange, Osage (spp.)
Orange, Osage 'Double O' Orange, Satsuma
Orange, Sweet (spp.) Orange, Sweet 'Dwarf Valencia'
Orange, Temple Orange, Trifoliat (spp.)
'Orchid' Saucer Magnolia: soulangianahybrid Orchid Tree
Orchid Tree, Hong Kong Orchid Tree, Purple
Orchid Tree, Variegated (spp.) Orchid Tree, Variegated 'Candida'
Orchid Tree, White Orchid Tree: grandidieri
Orchid Tree: spp.