Spermacoce articularis 
Spiked Centaury 
Spotted Gentian 
Spreading dogbane 
Spring Gentian 
Squinancywort 
Star gentian 
Star jasmine 
Stiff marsh bedstraw 
Stranglewort 
String of Hearts 
Strophanthus gratus 
Swallow-Wort 
Swamp milkweed 
Sweet Woodruff 
Sweet-scented bedstraw 
Swertia bimaculata 
Swertia lugardae 
Sword-leaf dogbane 
Tabernaemontana amygdalifolia 
Tabernaemontana divaricata 
Tachiadenus carinatus 
Tahitian Gardenia 
Tasaigo