- Madagascar Periwinkle
- Madwort
- Māhoe
- Maiden Pink
- Maidenhair spleenwort
- Male fern
- Mallow Bindweed
- Maltese star-thistle
- Man Orchid
- Mānuka
- Mapleleaf viburnum
- Māpou
- Marginal wood fern
- Maritime Bushy Bluestem
- Maritime pine
- Marsh calla
- Marsh cinquefoil
- Marsh Crane's-bill
- Marsh cudweed
- Marsh fern
- Marsh fleabane
- Marsh grass-of-Parnassus
- Marsh Helleborine
- Marsh Labrador tea
- Marsh marigold
- Marsh Skullcap
- Marsh Thistle
- Marsh Woundwort
- Martagon Lily
- Marvel of Peru
- Mascarene Island leaf-flower
- Mason Valley Cholla
- Mastic
- Matted Sandmat
- Maximilian sunflower
- May Lily
- Mayapple
- Meadow buttercup
- Meadow Crane's-bill
- Meadow Deathcamas
- Meadow Fleabane
- Meadow Foxtail
- Meadow horsetail
- Meadow pea
- Meadow Pink
- Meadow Sage
- Meadow salsify
- Meadow Saxifrage
- Meadowsweet
- Mealy Blue Sage
- Mediterranean buckthorn
- Mediterranean fan palm
- Mediterranean lineseed
- Mediterranean spurge
- Mediterranean Stork's-bill
- Melancholy Thistle
- Menzies' baby blue eyes
- Menzies' Tree Moss
- Mesquite Mistletoe
- Mexican buckeye
- Mexican Fleabane
- Mexican Giant Cactus
- Mexican palo verde
- Mexican Poppy
- Mexican prickly poppy
- Mexican Primrose-willow
- Mexican Ruellia
- Mexican sunflower
- Mezereon
- Mignonette vine
- Mile-a-minute
- Mile-a-minute vine
- Mile-a-minute weed
- Military Orchid
- Milk thistle
- Milkmaids
- Milkmaids
- Miner's lettuce
- Miniature Lupine
- Mission manzanita
- Mock azalea
- Mock strawberry
- Mojave Yucca
- Monterey pine
- Montpellier Cistus
- Monument plant
- Moon Carrot
- Moonseed
- Moschatel
- Moss Campion
- Moth mullein
- Moth Vine
- Mountain Clover
- Mountain Deathcamas
- Mountain hemlock
- Mountain holly
- Mountain laurel
- Mountain Maple
- Mountain Melick
- Mountain Pride
- Mountain Spirea
- Mountain woodsorrel
- Mouse-ear cress
- Mouse-eared hawkweed
- Mule fat
- Multi-flowered Buttercup
- Multiflora rose
- Muscadine
- Musk Hyacinth
- Musk mallow
- Musk stork's-bill
- Musk thistle
- Mustang grape
- Myrtle
- Myrtle Wattle