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
Sorbus minima
Least Whitebeam
Sorbus porrigentiformis
Grey-leaved Whitebeam
Sorbus rupicola
Rock Whitebeam
Sorbus stenophylla
Llanthony Whitebeam
Sorbus torminalis
Wild Service-tree
Sparganium angustifolium
Floating Bur-reed
Sparganium erectum
Branched Bur-reed
Sparganium natans
Least Bur-reed
Sparmannia sp.
African Hemp
Spartina anglica
Common Cord-grass
Spathiphyllum blandum
Pleasant Peace Lily
Spathodea campanulata
African Tulip Tree
Spergula arvensis
Corn Spurrey
Spergularia marina
Lesser Sea-spurrey
Spergularia media
Greater Sea-spurrey
Spergularia rubra
Sand Spurrey
Spergularia rupicola
Rock Sea-spurrey
Spermacoce hispida
Shaggy Buttonweed
Spermacoce remota
Spiraea canescens
Himalayan Spiraea
Spiraea x rosalba
Intermediate Bridewort
Spiranthes romanzoffiana
Irish Lady's-tresses
Spiranthes spiralis
Autumn Lady's-tresses
Spirodela polyrhiza
Greater Duckweed
Stachys alpina
Limestone Woundwort
Stachys arvensis
Field Woundwort
Stachys byzantina
Lamb's-ear
Stachys germanica
Downy Woundwort
Stachys palustris
Marsh Woundwort
Stachys sylvatica
Hedge Woundwort
Stapelia variegata
Stellaria alsine
Bog Stitchwort
Stellaria aquatica
Water Chickweed
Stellaria graminea
Lesser Stitchwort
Stellaria holostea
Greater Stitchwort
Stellaria media
Common Chickweed
Stellaria neglecta
Greater Chickweed
Sternbergia lutea
Winter Daffodil
Streptocarpus saxorum
False African Violet
Strobilanthes alternata
Red-ivy