| Papaveraceae | Poppy family |
| Passifloraceae | Passion-flower family |
| Paulowniaceae | Paulownia family |
| Penthoraceae | Ditch stonecrop family |
| Phrymaceae | Lopseed family |
| Phytolaccaceae | Pokeweed family |
| Pinaceae | Pine family |
| Plantaginaceae | Plantain family |
| Platanaceae | Plane-tree family |
| Plumbaginaceae | Leadwort family |
| Poaceae | Grass family |
| Polemoniaceae | Phlox family |
| Polygalaceae | Milkwort family |
| Polygonaceae | Smartweed family |
| Polypodiaceae | Polypody family |
| Polytricacheae | Hair-cap moss family |
| Pontederiaceae | Water-hyacinth family |
| Portulacaceae | Purslane family |
| Potamogetonaceae | Pondweed family |
| Primulaceae | Primrose family |
| Pteridaceae | Maidenhair-fern family |