Index of plants by genus
| Species | Common Name | Family |
| Sagittaria graminea | Grass-leaved Arrowhead | Alismataceae |
| Sagittaria latifolia | Arrowhead | Alismataceae |
| Salix myricoides (glaucophylloides) | Blue-leaved Willow | Salicaceae |
| Salix humilis | Prairie Willow | Salicaceae |
| Salix interior | Sandbar Willow | Salicaceae |
| Sambucus canadensis | Elderberry | Caprifoliaceae |
| Sambucus racemosa | Red Elderberry | Caprifoliaceae |
| Sanguinaria canadensis | Bloodroot | Papaveraceae |
| Sanicula gregaria | Clustered Black Snakeroot | Apiaceae |
| Sarracenia purpurea | Pitcher Plant | Sarraceniaceae |
| Sassafras albidum | Sassafras | Lauraceae |
| Satureja vulgaris | Wild Basil | Lamiacaea |
| Saxifraga pensylvanica | Swamp Saxifrage | Saxifragaceae |
| Saxifraga virginiensis | Early Saxifrage | Saxifragaceae |
| Scheuchzeria palustris | Pod-grass | Scheuchzeriaceae |
| Scirpus atrovirens | Green Bulrush | Cyperaceae |
| Scirpus cyperinus | Woolgrass | Cyperaceae |
| Scirpus fluviatilis | River Bulrush | Cyperaceae |
| Scirpus pungens | Chairmaker's Rush | Cyperaceae |
| Scirpus validus | Great Bulrush | Cyperaceae |
| Scrophularia lanceolata | Early Figwort | Scrophulariaceae |
| Scrophularia marilandica | Maryland Figwort | Scrophulariaceae |
| Scutellaria epilobiifolia | Marsh Skullcap | Lamiaceae |
| Scutellaria lateriflora | Mad-dog Skullcap | Lamiaceae |
| Scutellaria parvula var. leonardii | Small Skullcap | Lamiaceae |
| Selaginella apoda | Meadow Spikemoss | Selaginellaceae |
| Senecio aureus | Golden Ragwort | Asteraceae |
| Senecio pauperculus | Balsam Ragwort | Asteraceae |
| Shepherdia argentea | Silver Buffaloberry | Elaeagnaceae |
| Shepherdia canadensis | Russet Buffaloberry | Elaeagnaceae |
| Silene regia | Royal Catchfly | Caryophyllaceae |
| Silene stellata | Starry Campion | Caryophyllaceae |
| Silphium integrifolium | Rosinweed | Asteraceae |
| Silphium laciniatum | Compass Plant | Asteraceae |
| Silphium perfoliatum | Cup Plant | Asteraceae |
| Silphium terebinthinaceum | Prairie Dock | Asteraceae |
| Sisyrinchium albidum | Common Blue-Eyed Grass | Iridaceae |
| Sisyrinchium angustifolium | Narrow-leaved Blue-eyed Grass | Iridaceae |
| Sium suave | Hemlock Water Parsnip | Apiaceae |
| Smilax ecirrata | Upright Carrion Flower | Smilacaceae |
| Smilax hispida | Bristly Greenbrier | Smilacaceae |
| Smilax lasioneura | Carrion Flower | Smilacaceae |
| Smilax rotundifolia | Green Brier | Smilacaceae |
| Solanum carolinense | Horse-nettle | Solanaceae |
| Solidago bicolor | Silverrod | Asteraceae |
| Solidago canadensis | Canada Goldenrod | Asteraceae |
| Solidago caesia | Blue-stemmed Goldenrod | Asteraceae |
| Solidago flexicaulis | Broad-leaved Goldenrod | Asteraceae |
| Solidago gigantea | Giant Goldenrod | Asteraceae |
| Solidago graminifolia | Grass-leaved Goldenrod | Asteraceae |
| Solidago juncea | Early Goldenrod | Asteraceae |
| Solidago nemoralis | Old-field Goldenrod | Asteraceae |
| Solidago ohioensis | Ohio Goldenrod | Asteraceae |
| Solidago patula | Swamp Goldenrod | Asteraceae |
| Solidago ptarmicoides | Prairie Goldenrod | Asteraceae |
| Solidago riddellii | Riddell's Goldenrod | Asteraceae |
| Solidago rigida | Stiff Goldenrod | Asteraceae |
| Solidago rugosa | Rough Goldenrod | Asteraceae |
| Solidago speciosa | Showy Goldenrod | Asteraceae |
| Solidago uliginosa | Bog Goldenrod | Asteraceae |
| Solidago ulmifolia | Elm-leaved Goldenrod | Asteraceae |
| Sorbus decora | Showy Mountain Ash | Rosaceae |
| Sorghastrum nutans | Indian Grass | Poaceae |
| Sparganium eurycarpum | Common Bur-Reed | Sparganiaceae |
| Sparganium americanum | American Bur-Reed | Sparganiaceae |
| Spartina pectinata | Prairie Cord Grass | Poaceae |
| Sphagnum spp. | Sphagnum moss | Sphagnaceae |
| Spiraea alba | Meadowsweet | Rosaceae |
| Spiraea tomentosa | Steeplebush | Rosaceae |
| Spiranthes cernua | Nodding Lady's Tresses | Orchidaceae |
| Sporobolus heterolepsis | Prairie Dropseed | Poaceae |
| Stachys tenuifolia | Smooth Hedge Nettle | Lamiaceae |
| Staphylea trifolia | Bladdernut | Staphyleaceae |
| Stipa spartea | Porcupine Grass | Poaceae |
| Streptopus lanceolatus | Rose Twisted-stalk | Liliaceae |
| Stylophorum diphyllum | Celandine Poppy | Papaveraceae |
| Symphoricarpos albus | Common Snowberry | Caprifoliaceae |
| Symplocarpus foetidus | Skunk Cabbage | Araceae |
© 2004 Michael Hough