| Maclura pomifera | Osage Orange |
| Magnolia kobus | Kobus Magnolia |
| Magnolia virginiana var. virginiana | Northern Sweetbay Magnolia |
| Magnolia ×soulangiana | Chinese Magnolia |
| Mahonia bealei | Leatherleaf Mahonia |
| Maianthemum canadense | Canada Mayflower |
| Maianthemum racemosum subsp. racemosum | Solomon's Plume |
| Malus pumila | Common Apple |
| Malva neglecta | Dwarf Cheeseweed |
| Matricaria discoidea | Pineapple-weed |
| Mazus pumilus | Japanese Mazus |
| Medeola virginiana | Indian Cucumber-root |
| Medicago lupulina | Black Medic |
| Medicago sativa | Alfalfa |
| Melanthium virginicum | Virginia Bunchflower |
| Melilotus albus | White Sweetclover |
| Melilotus officinalis | Yellow Sweetclover |
| Menispermum canadense | Canada Moonseed |
| Mentha arvensis | Field Mint |
| Mentha spicata | Spearmint |
| Mentha ×piperita | Peppermint |
| Mertensia virginica | Virginia Bluebells |
| Micranthes virginiensis | Virginia Saxifrage |
| Microstegium vimineum | Japanese Stilt Grass |
| Mikania scandens | Climbing Hempweed |
| Mimulus ringens | Square-stem Monkeyflower |
| Minuartia caroliniana | Pine Barren Sandwort |
| Minuartia michauxii var. michauxii | Rock Sandwort |
| Mirabilis nyctaginea | Heart-leaved Umbrella-wort |
| Mitchella repens | Partridge-berry |
| Mitella diphylla | Two-leaf Bishop's-cap |
| Mollugo verticillata | Green Carpetweed |
| Monarda clinopodia | Basil Beebalm |
| Monarda didyma | Oswego-tea Beebalm |
| Monarda fistulosa var. fistulosa | Wild Bergamot Beebalm |
| Monarda punctata subsp. punctata | Horsemint Beebalm |
| Monotropa hypopithys | American Pinesap |
| Monotropa uniflora | Indian-pipe |
| Morella cerifera | Southern Bayberry |
| Morus alba | White Mulberry |
| Morus rubra | Red Mulberry |
| Muscari botryoides | Common Grape-hyacinth |
| Myosotis discolor | Yellow-and-blue Forget-me-not |
| Myosotis laxa subsp. laxa | Small Forget-me-not |
| Myosotis macrosperma | Large-seed Forget-me-not |
| Myosotis scorpioides | True Forget-me-not |
| Myosotis stricta | Small-flowered Forget-me-not |
| Myosotis versicolor | Yellow-and-blue Forget-me-not |
| Myosoton aquaticum | Giant-chickweed |
| Myrica cerifera | Southern Bayberry |
| Myrica pusilla | Southern Bayberry |