Sinapis arvensis
Charlock
Sison amomum
Stone Parsley
Sisymbrium officinale
Hedge Mustard
Sisyrinchium bermudiana
Blue-eyed-grass
Smyrnium olusatrum
Alexanders
Smyrnium perfoliatum
Perfoliate Alexanders
Solanum dulcamara
Bittersweet
Solanum nigrum
Black Nightshade
Solanum physalifolium
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
Sonchus asper
Prickly Sow-thistle
Sonchus oleraceus
Smooth Sow-thistle
Sorbus aria
Common Whitebeam
Sorbus aucuparia
Rowan
Sparganium erectum
Branched Bur-reed
Sparganium natans
Least Bur-reed
Sparmannia sp.
African Hemp
Spartina anglica
Common Cord-grass
Spergula arvensis
Corn Spurrey