Index of plants by genus
| Species | Common Name | Family |
| Sagittaria graminea | Grass-leaved Arrowhead | Alismataceae |
| Sagittaria latifolia | Arrowhead | Alismataceae |
| Salix interior | Sandbar willow | Salicaceae |
| Sambucus canadensis | Elderberry | Caprifoliaceae |
| Sanguinaria canadensis | Bloodroot | Papaveraceae |
| Sanicula gregaria | Clustered Black Snakeroot | Apiaceae |
| Sarracenia purpurea | Pitcher Plant | Sarraceniaceae |
| Satureja vulgaris | Wild Basil | Lamiacaea |
| 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 marilandica | Maryland figwort | Scrophulariaceae |
| Scutellaria epilobiifolia | Marsh Skullcap | Lamiaceae |
| Scutellaria lateriflora | Mad-dog Skullcap | Lamiaceae |
| Scutellaria parvula var. leonardii | Small Skullcap | Lamiaceae |
| Silene regia | Royal Catchfly | 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 |
| Sium suave | Hemlock Water Parsnip | Apiaceae |
| Smilax ecirrata | Upright Carrion Flower | Smilacaceae |
| Smilax lasioneura | Carrion Flower | Smilacaceae |
| Smilax rotundifolia | Green Brier | Smilacaceae |
| Solidago canadensis | Canada Goldenrod | Asteraceae |
| Solidago caesia | Blue-Stemmed Goldenrod | Asteraceae |
| Solidago flexicaulis | Broad-Leaved Goldenrod | Asteraceae |
| Solidago graminifolia | Grass-Leaved Goldenrod | Asteraceae |
| Solidago nemoralis | Old-Field Goldenrod | Asteraceae |
| Solidago ohioensis | Ohio Goldenrod | Asteraceae |
| Solidago rigida | Stiff Goldenrod | Asteraceae |
| Sorbus decora | Showy Mountain Ash | Rosaceae |
| Sorghastrum nutans | Indian Grass | Poaceae |
| Sparganium eurycarpum | Common Bur-Reed | Sparganiaceae |
| Spartina pectinata | Prairie Cord Grass | Poaceae |
| Spiraea alba | Meadowsweet | Rosaceae |
| Sporobolus heterolepsis | Prairie Dropseed | Poaceae |
| Stachys tenuifolia | Smooth Hedge Nettle | Lamiaceae |
| Staphylea trifolia | Bladdernut | Staphyleaceae |
| Stipa spartea | Porcupine Grass | Poaceae |
| Symphyotrichum azureus | Sky-Blue Aster | Asteracea |
| Symphyotrichum borealis | ||
| Symphyotrichum laevis | ||
| Symphyotrichum novae-angliae | New England Aster | Asteraceae |
| Symphyotrichum pilosa | ||
| Symphyotrichum | ||
| Symphyotrichum sagittifolius | ||
| Symplocarpus foetidus | Skunk Cabbage | Araceae |
© 2004 Michael Hough