Nymphoides peltata
Fringed Water-lily
Ochrolechia parella
Crab-eye Lichen
Odontites vernus
Red Bartsia
Oenanthe crocata
Hemlock Water-dropwort
Oenanthe fistulosa
Tubular Water-dropwort
Oenanthe pimpinelloides
Corky-fruited Water-dropwort
Oenothera biennis
Common Evening-primrose
Oenothera stricta
Fragrant Evening-primrose
Olearia macrodonta
New Zealand Holly
Ononis repens
Common Restharrow
Ononis spinosa
Spiny Restharrow
Ophioglossum vulgatum
Adder's-tongue
Ophrys apifera
Bee Orchid
Ophrys insectifera
Fly Orchid
Orchis mascula
Early-purple Orchid
Oreopteris limbosperma
Lemon-scented Fern
Ornithopus perpusillus
Bird's-foot
Orobanche hederae
Ivy Broomrape
Orobanche rapum-genistae
Greater Broomrape
Orthilia secunda
Serrated Wintergreen
Osmunda regalis
Royal Fern
Oxalis acetosella
Wood-sorrel
Oxybasis rubra
Red Goosefoot
Papaver cambricum
Welsh Poppy