Oenanthe fistulosa
Tubular Water-dropwort
Oenanthe lachenalii
Parsley Water-dropwort
Oenanthe silaifolia
Narrow-leaved Water-dropwort
Oenothera biennis
Common Evening-primrose
Olearia macrodonta
New Zealand Holly
Ononis reclinata
Small Restharrow
Ononis repens
Common Restharrow
Ophioglossum azoricum
Small Adder's-tongue
Ophioglossum vulgatum
Adder's-tongue
Ophrys apifera
Bee Orchid
Ophrys fuciflora
Late Spider-orchid
Ophrys insectifera
Fly Orchid
Orchid 'Butterfly Wings'
Orchis mascula
Early-purple Orchid
Ornithogalum nutans
Drooping Star-of-Bethlehem
Ornithogalum pyrenaicum
Spiked Star-of-Bethlehem
Ornithopus perpusillus
Bird's-foot
Orobanche caryophyllacea
Bedstraw Broomrape
Orobanche hederae
Ivy Broomrape
Orobanche minor
Common Broomrape
Orobanche picridis
Oxtongue Broomrape
Orobanche purpurea
Yarrow Broomrape
Orobanche rapum-genistae
Greater Broomrape
Orthilia secunda
Serrated Wintergreen