Sitka willow 
Slender Three-Seeded Mercury 
Slender violet-bush 
Slipper plant 
Small Poranthera 
Small White Violet 
Small-leaved Plane 
Smoketree spurge 
Snow on the mountain 
Snuff-box tree 
Spotted Spurge 
Spotted St. John's-wort 
Spurge Nettle 
St. Andrew's Cross 
St. John's wort 
Sticky Flax 
Stinking Passionflower 
Stream Violet 
Stream violet 
Striped Cream Violet 
Sudanese Tree-Euphorbia 
Sun Spurge 
Sweet Spurge 
Sweet Violet