Index of plants by genus
| Species | Common Name | Family |
| Parnassia glauca | Fen Grass of Parnassus | Saxifragaceae |
| Parthenocissus inserta | Thicket Creeper | Vitaceae |
| Parthenocissus quinquefolia | Virginia Creeper | Vitaceae |
| Pedicularis canadensis | Wood Betony | Scrophulariaceae |
| Penstemon digitalis | Foxglove Beardstongue | Scrophulariaceae |
| Penthorum sedoides | Ditch Stonecrop | Saxifragaceae |
| Phlox glaberrima | Marsh Phlox | Polemoniaceae |
| Phlox pilosa | Prairie Phlox | Polemoniaceae |
| Phryma leptostachya | American Lopseed | Phrymaceae |
| Phyla lanceolata | Lance-leaf Fog-fruit | Verbenaceae |
| Phytolacca americana | Pokeweed | Phytolaccaceae |
| Physocarpus opulifolius | Eastern Ninebark | Rosaceae |
| Physostegia virginiana | Obedient Plant | Lamiaceae |
| Picea mariana | Black Spruce | Pinaceae |
| Picea rubens | Red Spruce | Pinaceae |
| Pilea pumila | Clearweed | Urticaceae |
| Pinus banksiana | Jack Pine | Pinaceae |
| Pinus resinosa | Red Pine | Pinaceae |
| Pinus strobus | White Pine | Pinaceae |
| Platanthera clavellata | Green Wood Orchid | Orchidaceae |
| Platanus occidentalis | Sycamore | Plantaceae |
| Podophyllum peltatum | Mayapple | Berberidaceae |
| Pogonia ophioglossoides | Rose Pagonia | Orchidaceae |
| Polemonium reptans | Jacob's Ladder | Polemoniaceae |
| Polygonum sp. | ||
| Polygala polygama | Racemed Milkwort | Polygalaceae |
| Polygala senega | Seneca Snakeroot | Polygalaceae |
| Polymnia canadensis | Pale Leafcup | Asteraceae |
| Polygonatum canaliculatum | Smooth Solomon's Seal | Liliaceae |
| Polypodium virginianum | Rock Polypody | Polypodiaceae |
| Polystichum acrostichoides | Christmas Fern | Dryopteridaceae |
| Populus deltoides | Eastern Cottonwood | Salicaceae |
| Populus tremuloides | Trempling Aspen | Salicaceae |
| Potentilla anserina | Silverweed | Rosaceae |
| Potentilla fruticosa | Shrubby Cinquefoil | Rosaceae |
| Potentilla palustris | Marsh Cinquefoil | Rosaceae |
| Potentilla simplex | Common Cinquefoil | Rosaceae |
| Potomogeton sp. | ||
| Prenanthes altissima | Tall White Lettuce | Asteraceae |
| Prunella vulgaris var. lanceolata | Self Heal | Lamiaceae |
| Prunus americana | American Plum | Rosaceae |
| Prunus pumila | Sand Cherry | Rosaceae |
| Prunus serotina | Wild Black Cherry | Rosaceae |
| Prunus virginiana | Chokecherry | Rosaceae |
| Ptelea trifolia |