Science magazines
- Robust Spineflower
- Rock Gnome Lichen
- Roseate Tern
- Rough Pigtoe
- Rough Popcornflower
- Rough Rabbitsfoot
- Rough-leaved Loosestrife
- Round Rocksnail
- Round-leaved Chaff-flower
- Royal Marstonia Snail
- Rugel's Pawpaw
- Running Buffalo Clover
- Ruth's Golden Aster
- Sacramento Mountains Thistle
- Sacramento Orcutt Grass
- Sacramento Prickly Poppy
- Sacramento Splittail
- Saint Francis' Satyr Butterfly
- Salt Marsh Bird's-beak
- Salt Marsh Harvest Mouse