Orbea umbracula Orbignya phalerata
Oreocereus celsianus Origanum x 'Kents Beauty'
Origanum dictamnus Origanum dictamnus 'Amargcus Dictamnus'
Origanum laevigatum 'Herrenhausen' Origanum laevigatum 'Rosenkuppel'
Origanum majorana 'Compactum' Origanum majorana 'Sicillian'
Origanum pulchellum Origanum rotundifolium
Origanum syriacum Origanum vulgare
Origanum vulgare 'Aureum' Origanum vulgare 'Thumbles'
Origanum vulgare 'Variegatum' Origanum vulgare ssp. hirtum 'Noa'
Ornithogalum dubium 'Orange Cream' Ornithogalum oligophyllum
Ornithogalum umbellatum Orontium aquaticum
Orostachys iwarenge Orthosiphon labiatus
Orthosiphon stramineus Orthosiphon stramineus 'Albus'
Oryza sativa 'Black Madras' Osbeckia crinita
Osmanthus americanus Osmanthus x burkwoodii
Osmanthus x fortunei Osmanthus fragrans
Osmanthus fragrans 'Fudingzhu' Osmanthus heterophyllus
Osmanthus heterophyllus 'Aureomarginatus' Osmanthus heterophyllus 'Goshiki'
Osmanthus heterophyllus 'Gulftide' Osmanthus heterophyllus 'Kembu'
Osmanthus heterophyllus 'Rotundifolius' Osmanthus heterophyllus 'Variegatus'
Osmoxylon spp. Osmunda cinnamonea
Osmunda claytonia Osmunda regalis
Osmunda regalis 'Purpurescens' Osmunda regalis var. spectabilis
Osteospermum 'Brightside' Osteospermum 'Flower Power Pink'
Osteospermum 'Impassion White' Osteospermum 'Passion Mix'
Osteospermum 'Pinwheel Purple' Osteospermum 'Pinwheel Rose'
Osteospermum 'Pinwheel White Eye' Osteospermum 'Polar Star'
Osteospermum 'Seikilrem (Lemon Symphony)' Osteospermum 'Sparkler'
Osteospermum 'Summeretime Pink Charme' Osteospermum 'Summertime Sweet Blue Sunrise'
Osteospermum 'Summertime Sweet White' Osteospermum 'Tradewinds™ Deep Purple'
Osteospermum 'Tradewinds™ Light Purple' Osteospermum 'Tradewinds™ Pink'
Osteospermum ecklonis Osteospermum ecklonis 'Akope'
Osteospermum ecklonis 'Balostlueye (Blue Eyed Beauty)' Osteospermum fruticosum
Osteospermum fruticosum 'Trailing' Ostrya carpinifolia
Ostrya virginiana Otacanthus caeruleus
Otatea acuminata Othonna capensis
Oxalis crassipes Oxalis oregana
Oxalis purpurea Oxalis purpurea 'Garnet'
Oxalis regnellii Oxalis regnellii 'Atropurpurea'
Oxalis spiralis ssp. vulcanicola Oxalis stricta
Oxalis tetraphylla Oxalis triangularis
Oxalis valdiviensis 'Lucky Gold' Oxalis viops
Oxalis vulcanicola 'Burgundy' Oxalis vulcanicola 'Copper Glow'
Oxalis vulcanicola 'Molten Lava™' Oxydendrum arboreum
Oxydendrum arboreum 'Pendula' Ozothamnus diosmifolius
Ozothamnus rosmarinifolius 'Silver Jubilee' Pachira aquatica
Pachira sp. Pachycereus hollianus
Pachycereus marginatus Pachycereus pringlei
Pachycereus schottii Pachycereus schottii var. monstrosus
Pachycormus discolor