- Pacific Bleeding Heart
- Pacific coralroot
- Pacific Dogwood
- Pacific hound's tongue
- Pacific madrone
- Pacific ninebark
- Pacific pea
- Pacific poison oak
- Pacific Sanicle
- Pacific trillium
- Pacific yew
- Painted spurge
- Painted trillium
- Pale flax
- Pale jewelweed
- Pale smartweed
- Pale Stonecrop
- Pale-spiked lobelia
- Palm-tree Moss
- Pampas Grass
- Panicled aster
- Papaya
- Paper birch
- Paper mulberry
- Parrot's feather
- Partridge pea
- Partridgeberry
- Partridgefoot
- Peach
- Peach-leaved Bellflower
- Peacock flower
- Pearl Milkweed
- Pearly everlasting
- Pecan
- Pellitory-of-the-wall
- Peninsular fishhook cactus
- Pennyroyal
- Peppervine
- Perennial Cornflower
- Perennial honesty
- Perennial Ryegrass
- Perennial Sow Thistle
- Perennial Wall-rocket
- Perennial Yellow-woundwort
- Perfoliate Penny-cress
- Persian silk tree
- Persian walnut
- Peruvian Pepper Tree
- Peruvian zinnia
- Petty Spurge
- Philadelphia fleabane
- Pickerelweed
- Pigeonberry
- Pincushion Moss
- Pineapple-weed
- Pinesap
- Pinewood bracken
- Pinewoods geranium
- Pink Honeysuckle
- Pink Ivy-leaved Speedwell
- Pink knotweed
- Pink Lady Fingers
- Pink lady's slipper
- Pink mountainheath
- Pink Sundew
- Pink-sorrel
- Pinkladies
- Pipsissewa
- Pitch pine
- Plains coreopsis
- Plains Pricklypear
- Poet's Narcissus
- Pointed-leaved tick-trefoil
- Pointleaf manzanita
- Poison hemlock
- Poke milkweed
- Pomegranate
- Porcelain Berry
- Possumhaw
- Post oak
- Pot marigold
- Poverty Weed
- Prairie dock
- Prairie false indigo
- Prairie Nymph
- Prairie pasqueflower
- Prairie phlox
- Prairie smoke
- Prairie Tea
- Prairie trillium
- Prickly cucumber
- Prickly lettuce
- Prickly Russian Thistle
- Prickly sowthistle
- Prickly tree-clubmoss
- Prickly Wild Rose
- Pride of Madeira
- Primrose
- Princess tree
- Procumbent Pearlwort
- Prostrate Knotweed
- Prostrate sandmat
- Puncture vine
- Purple Chinese Houses
- Purple Cleome
- Purple coneflower
- Purple Cress
- Purple crownvetch
- Purple foxglove
- Purple Gromwell
- Purple Heart
- Purple loosestrife
- Purple owl's-clover
- Purple passionflower
- Purple pitcher plant
- Purple prairie clover
- Purple salsify
- Purple Sanicle
- Purple Saxifrage
- Purple Toadflax
- Purple viper's-bugloss
- Purple Wood Sage
- Purple woodsorrel
- Purple-flowered raspberry
- Purple-stem cliffbrake
- Purpletop tridens
- Purpletop vervain
- Putty root
- Pyramidal orchid