Oenanthe crocata
Hemlock Water-dropwort
Oenanthe fistulosa
Tubular Water-dropwort
Omphalina ericetorum
Ononis repens
Common Restharrow
Ophioglossum vulgatum
Adder's-tongue
Ophrys apifera
Bee Orchid
Orchis mascula
Early-purple Orchid
Oreopteris limbosperma
Lemon-scented Fern
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
Pararge aegeria
Speckled Wood
Parietaria judaica
Pellitory-of-the-wall
Paris quadrifolia
Herb-paris
Pedicularis palustris
Marsh Lousewort
Pedicularis sylvatica
Lousewort
Pellia spp.
Persicaria amphibia
Amphibious Bistort
Persicaria hydropiper
Water-pepper
Persicaria lapathifolia
Pale Persicaria