Red-seeded dandelion 
Redflower Ragleaf 
Redpurple Ragwort 
Rice flower 
Rigid Whitetop Aster 
Rock Isotome 
Rock Isotome 
Rock Lettuce 
Rock Phagnalon 
Rock thistle 
Rose Rush 
Rosy pussytoes 
Rough blazing star 
Rough Cocklebur 
Rough Hawk's-Beard 
Rough Hawkbit 
Rough Hawkweed 
Rough-leaved Michauxia 
Roundleaf ragwort 
Royal bluebell 
Rudbeckia californica 
Rudbeckia subtomentosa 
Rush pussytoes 
Rush Skeletonweed