Poisonvetch _Astragalus_ 30 Pokeberry _Phytolacca_ 50 Polemonium _Polemonium_ 50 Polygala _Polygala_ 50 Polypogon _Polypogon_ 25 Polytaenia _Polytaenia_ 50 Pondweed _Potamogeton_ 29 Poolmat _Zannichellia_ 30 Poplar _Populus_ 57 Poppymallow _Callirhoë_ 38 Porcupinegrass _Stipa spartea_ 26 Portulaca _Portulaca_ 50 Potato _Solanum tuberosum_ 53 Potatobean _Apios_ 30 Prairieclover _Petalostemum_ 33 Prairieconeflower _Ratibida_ 51 Prairiegentian _Eustoma_ 42 Pricklyash _Xanthoxylum_ 59 Pricklypear _Opuntia_ 48 Pricklypoppy _Argemone_ 36 Princesplume _Stanleya_ 53 Proso _Panicum miliaceum_ 23 Puncturevine _Tribulus_ 54 Purplerocket _Iodanthus_ 45 Purpletop _Tridens flavus_ 26 Purslane _Portulaca_ 50 Pussytoes _Antennaria_ 35 Quackgrass _Agropyron repens_ 18 Quakinggrass _Briza_ 19 Quickweed _Galinsoga_ 43 Quillwort _Isoëtes_ 28 Rabbitbrush _Chrysothamnus_ 56 Radish _Raphanus_ 51 Ragweed _Ambrosia_ 35 Rainlily _Cooperia_ 29 Rape _Brassica rapa_ 38 Raspberry _Rubus_ 58 Rattlesnakefern _Botrychium_ 28 Rattlesnakeroot _Prenanthes_ 51 Ravennagrass _Erianthus ravennae_ 21 Razorsedge _Scleria_ 28 Redbud _Cercis_ 31, 56