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Name	Species	Common Name
Odontites	vernus	Red Bartsia
Oenanthe	aquatica	Fine-leaved Water Dropwort
Oenanthe	crocata	Hemlock Water Dropwort
Oenanthe	fistulosa	Tubular Water Dropwort
Oenanthe	fluviatilis	River Water Dropwort
Oenanthe	lachenalii	Parsley Water Dropwort
Oenanthe	pimpinelloides	Corky-fruited Water Dropwort
Oenanthe	silaifolia	Narrow-leaved Water Dropwort
Onobrychis	vicifolia	Sainfoin
Ononis	reclinata	Small Restharrow
Ononis	repens	Common Restharrow
Ononis	spinosa	Spiny Restharrow
Ophioglossum	azoricum	Small Adder’s-tongue
Ophioglossum	lusitanicum	Least Adder’s-tongue
Ophioglossum	vulgatum	Adder’s-tongue
Ophrys	apifera	Bee Orchid
Ophrys	fuciflora	Late Spider Orchid
Ophrys	insectifera	Fly Orchid
Ophrys	sphegodes	Early Spider Orchid
Orchis	laxiflora	Loose-flowered Orchid
Orchis	mascula	Early-purple Orchid
Orchis	militaris	Military Orchid
Orchis	morio	Green-winged Orchid
Orchis	purpurea	Lady Orchid
Orchis	simia	Monkey Orchid
Orchis	ustulata	Burnt Orchid
Oreopteris	limbosperma	Lemon-scented Fern
Origanum	vulgare	Wild Marjoram
Ornithogalum	angustifolium	Star-of-Bethlehem
Ornithogalum	pyrenaicum	Spiked Star-of-Bethlehem
Ornithopus	perpusillus	Bird’s-foot
Ornithopus	pinnatus	Orange Bird’s-foot
Orobanche	alba	Thyme Broomrape
Orobanche	artemisiae-campestris	Oxtongue Broomrape
Orobanche	caryophyllacea	Bedstraw Broomrape
Orobanche	elatio	Knapweed Broomrape
Orobanche	hederae	Ivy Broomrape
Orobanche	minor	Common Broomrape
Orobanche	purpurea	Yarrow Broomrape
Orobanche	rapum-genistae	Greater Broomrape
Orobanche	reticulata	Thistle Broomrape
Orthilia	secunda	Serrated Wintergreen
Osmunda	regalis	Royal Fern
Otanthus	maritimus	Cottonweed
Oxalis	acetosella	Wood-sorrel
Oxyria	digyna	Mountain Sorrel
Oxytropis	campestris	Yellow Oxytropis
Oxytropis	halleri	Purple Oxytropis