Weed Herbarium – by Scientific Name
| Panicum capillare | witchgrass | Poaceae (Graminae) - Grass Family |
| Panicum dichotomiflorum | fall panicum | Poaceae (Graminae) - Grass Family |
| Panicum virgatum | switchgrass | Poaceae (Graminae) - Grass Family |
| Parthenocissus quinquefolia | Virginia creeper | Vitaceae - Grape Family |
| Paspalum dilatatum | dallis grass | Poaceae (Graminae) - Grass Family |
| Paspalum setaceum | paspalum | Poaceae (Graminae) - Grass Family |
| Pastinaca sativa | wild parsnip | Apiaceae (Umbelliferae) - Carrot Family |
| Persicaria arifolia | see - Polygonum arifolium | |
| Persicaria maculosa | see - Polygonum persicaria | |
| Persicaria pensylvanica | see - Polygonum pensylvanicum | |
| Persicaria sagittata | see - Polygonum sagittatum | |
| Persicaria virginica | see - Tovara virginiana |
| Petasites hybridus | butterburdock | Asteraceae (Compositae) - Aster or Sunflower Family |
| Phalaris arundinacea | reed canary grass | Poaceae (Graminae) - Grass Family |
| Phleum pratense | timothy | Poaceae (Graminae) - Grass Family |
| Phragmites communis | see - Phragmites australis | |
| Phragmites australis | common reed | Poaceae (Graminae) - Grass Family |
| Phytolacca americana | common pokeweed | Phytolaccaceae - Pokeweed Family |
| Pilea pumila | clearweed | Urticaceae - Nettle Family |
| Plantago lanceolata | narrowleaf plantain | Plantaginaceae - Plantain Family |
| Plantago major | broadleaf plantain | Plantaginaceae - Plantain Family |
| Poa annua | annual bluegrass | Poaceae (Graminae) - Grass Family |
| Poa bulbosa | bulbous bluegrass | Poaceae (Graminae) - Grass Family |
| Polygonum virginianum | see - Tovara virginiana | |
| Polygonum arifolium | Halberd-leaved tearthumb | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum aviculare | prostrate knotweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum cilinode | black fringed knotweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum convolvulus | wild buckwheat | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum cuspidatum | Japanese knotweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum pensylvanicum | Pennsylvania smartweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum persicaria | lady's thumb smartweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum sachalinense | giant knotweed | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum sagittatum | arrowleaf tear-thumb | Polygonaceae - Smartweed or Buckwheat Family |
| Polygonum scandens | hedge smartweed | Polygonaceae - Smartweed or Buckwheat Family |
| Portulaca oleracea | common purslane | Portulacaceae - Purslane Family |
| Potentilla argentea | silvery cinquefoil | Rosaceae - Rose Family |
| Potentilla norvegica | rough cinquefoil | Rosaceae - Rose Family |
| Potentilla recta | sulfur cinquefoil | Rosaceae - Rose Family |
| Potentilla simplex | old field cinquefoil | Rosaceae - Rose Family |
| Prunella vulgaris | heal-all | Lamiaceae (Labiatae) - Mint Family |
| Pteridium aquilinum | bracken fern | Polypodiaceae - Fern Family |
| Pueraria lobata | see - Pueraria montana | |
| Pueraria montana | kudzu | Fabaceae (Leguminosae) - Pea or Bean Family |