- Mallow, Common
- Mallow, Musk
- Maple, Mountain
- Maple-leaved Viburnum
- Marigold, Larger Bur
- Marigold, Marsh
- Mayapple
- Meadowbeauty, Virginia
- Meadow Parsnip, Smooth
- Meadow Rue, Early
- Meadow Rue, Tall
- Meadow Rue, Waxy
- Meadowsweet, White
- Mertensia
- Mexican Tea
- Miami Mist
- Mild Water Pepper
- Milkweed, Clasping
- Milkweed, Common
- Milkweed, Four-leaved
- Milkweed, Poke
- Milkweed, Purple
- Milkweed, Red
- Milkweed, Swamp
- Milkweed, White
- Milkweed, Whorled
- Milkwort, Bitter
- Milkwort, Blood
- Milkwort, Curtiss'
- Milkwort, Whorled
- Milkvetch, Canada
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- Minniebush
- Mistflower
- Miterwort
- Moccasin Flower
- Moneywort
- Monkey Flower
- Monkey Flower, Musky
- Monkey Flower, Winged
- Monkshood, Blue or Wild
- Monkshood, White or Trailing White
- Morel
- Morning-glory, Common
- Morning-glory, Ivy-Leaf
- Morning-glory, White
- Morrow's Fly Honeysuckle
- Mother-of-thyme
- Motherwort
- Mountain Anemone
- Mountain Fetterbush
- Mountain Laurel
- Mountain Mint, Hoary
- Mountain Mint, Narrow-leaved
- Mountain Mint, Short-tooth
- Mountain Mint, Torrey's
- Mountain Mint, Virginia
- Mountain Rosebay
- Mullein, Common
- Mullein, Moth
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