Ranunculus gmelinii (Gmelin's buttercup)

Rudbeckia maxima (great coneflower)
Ruellia caroliniensis ssp. caroliniensis var. caroliniensis
Ruellia strepens (limestone wild petunia)
Rumex acetosa
Rumex acetosa (garden sorrel)
Rumex acetosella
Rumex acetosella (common sheep sorrel)
Rumex altissimus (pale dock)
Rumex conglomeratus
Rumex conglomeratus (clustered dock)
Rumex crispus
Rumex hastatulus (heartwing sorrel)
Rumex obtusifolius
Rumex salicifolius var. mexicanus (Mexican dock)
Rumex sanguineus
Rumex sanguineus (redvein dock)
Ruppia cirrhosa (spiral ditchgrass)
Ruppia maritima (widgeongrass)
Ruscus aculeatus
Ruscus hypoglossum
Russia
Russula acetolens
Russula adusta
Russula amoenicolor
Russula anatina
Russula aurea
Russula cessans
Russula chloroides
Russula cyanoxantha