Senna fistula
Golden Shower Tree
Senna obtusifolia
Sicklepod
Sequoia sempervirens
Coastal Redwood
Sequoiadendron giganteum
Wellingtonia
Serratula tinctoria
Saw-wort
Seseli libanotis
Moon Carrot
Setaria verticillata
Hooked Bristlegrass
Setaria viridis
Green Bristle-grass
Sherardia arvensis
Field Madder
Sibthorpia europaea
Cornish Moneywort
Sicyos edulis
Chayote
Sida acuta
Common Wireweed
Sida rhombifolia
Arrowleaf Sida
Silaum silaus
Pepper-saxifrage
Silene acaulis
Moss Campion
Silene armeria
Sweet-William Catchfly
Silene chalcedonica
Maltese-Cross
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
Solandra grandiflora
Showy Chalicevine
Solanum americanum
American Black Nightshade
Solanum chenopodioides
Tall Nightshade
Solanum dulcamara
Bittersweet
Solanum erianthum
Velvet Nightshade
Solanum melongena
Eggplant
Solanum nigrum
Black Nightshade
Solanum nitidibaccatum
Green Nightshade
Solanum torvum
Pendejera
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
Sonneratia caseolaris
Mangrove Apple
Sorbus aria
Common Whitebeam
Sorbus aucuparia
Rowan
Sorbus cambrensis
Welsh Whitebeam
Sorbus leptophylla
Thin-leaved Whitebeam
Sorbus leyana
Ley's Whitebeam
Sorbus minima
Least Whitebeam
Sorbus porrigentiformis
Grey-leaved Whitebeam
Sorbus rupicola
Rock Whitebeam
Sorbus stenophylla
Llanthony Whitebeam
Sorbus torminalis
Wild Service-tree
Sorbus x motleyi
Sparganium angustifolium
Floating Bur-reed
Sparganium erectum
Branched Bur-reed
Sparganium natans
Least Bur-reed