Ramonda - After French politician, explorer and botanist Louis Ramond de Carbonnieres.
Reseda - Fragrant flowers, commonly known as Mignonette. Reseda derives from the Latin resedo "to heal." The name was first used by Pliny for a species of mignonette that was believed to contain medicinal properties.
Rhodanthe - From the Greek ῥόδον (rhodon) "rose" and ἄνθος (anthos) "flower," referring to the colour of the flowers.
Rhodora - A flowering shrub, derived from the Greek ῥόδον (rhodon) "rose."
Rhus (roos) - From the Ancient Greek name for the plant, ῥοῦς (Rhous).
Rivina - Named after A. Q. Rivinus, professor of botany at Leipzig.
Roella - Named for Dutch botanist George Roelle.
Rosa - Rosa, of course, has long been used as a name, but it makes this list due to some interesting species names: Alba "white," Alpina "alpine," Carolina "from Carolina," Damascena "Damask Rose," Ferox "fierce," Indica "from India," Lucida "bright," Lutea "yellow," Polyantha "many flowers," Pomifera "apple-bearing."
Rubus - Most likely from the Latin ruber "red," the colour of the fruit of many species.
Rumex - From the Latin name for sorrel. It derives from the Latin ruma "flowing" or "to bring to me" in reference to drinking liquid. The Romans used to suck on sorrel leaves to alleviate thirst.
Ruscus - Commonly known as butcher's broom, sweet broom, pettigree or box holly. It is said to be a corruption of bruscus, from the Old Celtic brus "box" and kelen "holly."
Ruta - The ancient name for rue.
Salix- The latin name for willow. It has been suggested that the name ultimately derives from te Old Celtic sal "near" and lis "water."
Saxifraga - While this "stone-breaker" doesn't rate much in the name stakes, it does have some intriguing species names: Altissima "very high," Caesia "grey leaved," Cymbalaria, Florulenta "full flower," Tenella "delicate," Valentina.
Solandra - Named for Swedish explorer Daniel Charles Solander.
Sollya - Named after naturalist R.H. Solly.
Sophora - Derived from sophera, the Arabic name for a tree with pea-shaped flowers.
Stephanandra - From the Greek στέφανος (stephanos) "crown" and ἄνδρος (andros) "stem."