Plants — R
- Rafflesia
- Rafflesia kerrii
- Randia longiloba
- Ranunculus acris Meadow Buttercup
- Ranunculus bulbosus Bulbous Crowfoot
- Ranunculus glacialis Glacier Buttercup
- Ranunculus japonicus
- Ranunculus repens Creeping Buttercup
- Ranunculus reptans Creeping Spearwort
- Raphanus raphanistrum Charlock
- Raphanus sativus Cultivated Radish
- Rauvolfia Devil's-Pepper
- Rauvolfia serpentina Indian Snakeroot
- Rauvolfia tetraphylla Be Still Tree
- Rehmannia
- Rehmannia glutinosa Chinese-foxglove
- Renealmia alpinia jenjibre-de-jardin
- Reseda lutea Cut Leaved Mignonette
- Reseda luteola Dyer's Mignonette
- Reynoutria japonica Asian Knotweed
- Reynoutria multiflora Chinese fleece flower
- Rhamnus cathartica Buckthorn
- Rhamphospermum nigrum Black Mustard
- Rhaponticum carthamoides
- Rheum officinale Chinese rhubarb
- Rheum palmatum Chinese rhubarb
- Rheum rhabarbarum Rhubarb
- Rheum ribes Syrian rhubarb
- Rhinacanthus nasutus
- Rhizophora apiculata
- Rhizophora mangle American Mangrove
- Rhizophora mucronata Asiatic Mangrove
- Rhodiola crenulata
- Rhodiola rosea Arctic root
- Rhododendron aureum
- Rhododendron championiae Champion's Rhododendron
- Rhododendron molle
- Rhododendron mucronulatum Korean rhododendron
- Rhododendron mucronulatum f. albiflorum
- Rhododendron schlippenbachii Royal azalea
- Rhododendron tomentosum Marsh Labrador Tea
- Rhodomyrtus tomentosa Ceylon hill-cherry
- Rhus chinensis Chinese gall
- Rhus coriaria Elm-Leaved Sumac
- Rhus glabra Red Sumac
- Rhus taitensis Sumac
- Rhynchostylis retusa Foxtail Orchid
- Ribes nigrum Black Currant
- Richeria grandis
- Ricinus communis Castor
- Robinia pseudoacacia Black Locust
- Rohdea japonica Japanese Sacred Lily
- Rorippa cantoniensis Chinese yellowcress
- Rorippa indica Diverse-leaf Yellowcress
- Rorippa sinuata spread yellow cress
- Rosa Rose
- Rosa californica California rose
- Rosa canina Common-briar
- Rosa × centifolia Burgundy rose
- Rosa chinensis Bengal rose
- Rosa cymosa
- Rosa × damascena Damask rose
- Rosa foetida Austrian Briar
- Rosa gallica Apothecary Rose
- Rosa glauca Red-leaved Rose
- Rosa laevigata Cherokee rose
- Rosa lucieae Memorial rose
- Rosa macrantha
- Rosa majalis Cinnamom Rose
- Rosa maximowicziana Maximowicz’s rose
- Rosa moschata Musk Rose
- Rosa multiflora Baby Rose
- Rosa nutkana Nootka rose
- Rosa ×odorata Tea rose
- Rosa rugosa Beach Rose
- Rubia Madders
- Rubia cordifolia Heart-leaf Indian madder
- Rubia tinctorum Dyer's madder
- Rubus crataegifolius Hawthorn-leaved Bramble
- Rubus idaeus American Red Raspberry
- Rubus occidentalis Black Raspberry
- Rubus saxatilis Greenland thornless blackberry
- Rubus sieboldii Molucca raspberry
- Ruehssia cundurango
- Ruellia prostrata Prostrate Wild Petunia
- Ruellia tuberosa Devil's Bit
- Rumex acetosa Sorrel
- Rumex acetosella Common Sheep Sorrel
- Rumex confertus Asiatic dock
- Rumex crispus
- Rumex hypogaeus Cape Spinach
- Ruscus aculeatus Butcher's-Broom
- Ruta Rue
- Ruta chalepensis Fringed Rue
- Ruta graveolens Ave Grace
- Rydingia integrifolia Otostegia integrifolia