Rosy pussytoes 
Rough blazing star 
Rough Cocklebur 
Rough Hawk's-Beard 
Rough Hawkbit 
Rough Hawkweed 
Roundleaf ragwort 
Rudbeckia californica 
Rudbeckia subtomentosa 
Rush pussytoes 
Rush Skeletonweed 
Russian knapweed 
Sagebrush false dandelion 
Sand Sagebrush 
Santa Barbara Daisy 
Santa Maria Feverfew 
Sanvitalia procumbens 
Saw-tooth Sage 
Saw-Wort 
Scabland sagebrush 
Scentless False Mayweed 
Scorzonera alpigena 
Scorzonera eriophora 
Scorzonera libanotica