Ranunculus nivalis (snow buttercup)

Slovenia
Smilax ecirrhata (upright carrionflower)
Smilax glauca (cat greenbrier)
Smilax pseudochina (bamboo vine)
Smilax rotundifolia (roundleaf greenbrier)
Smilax walteri (coral greenbrier)
Smyrnium perfoliatum
Solanum dulcamara
Solanum dulcamara (climbing nightshade)
Solanum nigrum
Solanum tuberosum
Soldato italiano in divisa durante la prima guerra mondiale
Solidago arguta var. boottii (Boott's goldenrod)
Solidago canadensis
Solidago curtisii (mountain decumbent goldenrod)
Solidago gigantea
Solidago sciaphila (shadowy goldenrod)
Solidago sphacelata (autumn goldenrod)
Solomon Islands
Somalia
Sonchus asper
Sonchus asper (spiny sowthistle)
Sorbus aria
Sorbus aucuparia
Sorbus chamaemespilus
South Africa
South Georgia and the South Sandwich Islands
Spain
Sparganium americanum (American bur-reed)

Image of Ranunculus nivalis (snow buttercup) 1
USDA-NRCS PLANTS Database / Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. Vol. 2: 107.