Scrophularia auriculata
Water Figwort
Scrophularia nodosa
Common Figwort
Scrophularia umbrosa
Green Figwort
Scutellaria galericulata
Skullcap
Scutellaria minor
Lesser Skullcap
Scyphiphora hydrophylacea
Nilad
Secale cereale
Rye
Sedum acre
Biting Stonecrop
Sedum album
White Stonecrop
Sedum anglicum
English Stonecrop
Sedum sexangulare
Tasteless Stonecrop
Seemannia sylvatica
Bolivian Sunset Gloxinia
Selaginella martensii
Variegated Spikemoss
Selaginella selaginoides
Lesser Clubmoss
Selaginella willdenowii
Peacock Fern
Selenicereus undatus
Pitahaya
Senecio cambrensis
Welsh Groundsel
Senecio inaequidens
Narrow-leaved Ragwort
Senecio sarracenicus
Broad-leaved Ragwort
Senecio squalidus
Oxford Ragwort
Senecio sylvaticus
Heath Groundsel
Senecio viscosus
Sticky Groundsel
Senecio vulgaris
Groundsel
Senna obtusifolia
Sicklepod
Sequoia sempervirens
Coastal Redwood
Sequoiadendron giganteum
Wellingtonia
Serratula tinctoria
Saw-wort
Sesuvium portulacastrum
Sea Purslane
Setaria palmifolia
Palm Grass
Setaria viridis
Green Bristle-grass
Sherardia arvensis
Field Madder
Sibthorpia europaea
Cornish Moneywort
Silaum silaus
Pepper-saxifrage
Silene acaulis
Moss Campion
Silene armeria
Sweet-William Catchfly
Silene conica
Sand Catchfly
Silene dioica
Red Campion
Silene flos-cuculi
Ragged-Robin
Silene gallica
Small-flowered Catchfly
Silene latifolia
White Campion
Silene noctiflora
Night-flowering Catchfly
Silene nutans
Nottingham Catchfly
Silene rupestris
Rock Campion
Silene uniflora
Sea Campion
Silene viscaria
Sticky Catchfly
Silene vulgaris
Bladder Campion
Silybum marianum
Milk Thistle
Simethis mattiazzii
Kerry Lily
Sinapis alba
White Mustard
Sinapis arvensis
Charlock
Sison amomum
Stone Parsley
Sisymbrium officinale
Hedge Mustard
Sisyrinchium bermudiana
Blue-eyed-grass
Sisyrinchium montanum
American Blue-eyed-grass
Smyrnium olusatrum
Alexanders
Smyrnium perfoliatum
Perfoliate Alexanders
Solanum chenopodioides
Tall Nightshade
Solanum dulcamara
Bittersweet
Solanum nigrum
Black Nightshade
Solanum nitidibaccatum
Green Nightshade
Soldanella alpina
Alpine Snowbell
Soleirolia soleirolii
Mind-your-own-business
Solidago canadensis
Canadian Goldenrod
Solidago gigantea
Early Goldenrod
Solidago virgaurea
Goldenrod
Sonchus arvensis
Perennial Sow-thistle
Sorbus aria
Common Whitebeam
Sorbus aucuparia
Rowan
Sorbus cambrensis
Welsh Whitebeam
Sorbus leptophylla
Thin-leaved Whitebeam