- Baldcypress
- Baldhip Rose
- Balkan toadflax
- Ballmoss
- Balloonplant
- Balsam fir
- Balsam poplar
- Banana Yucca
- Bank Haircap Moss
- Barnyardgrass
- Barren Brome
- Basswood
- Bastard Balm
- Bastard toadflax
- Bay laurel
- Beach Morning Glory
- Beach naupaka
- Beach Sheoak
- Beach strawberry
- Beach suncup
- Beaked hazelnut
- Bear oak
- Bear's breeches
- Bear's foot
- Bearberry
- Bee Orchid
- Beechdrops
- Beefsteak plant
- Bell Heather
- Belladonna Lily
- Bermuda buttercup
- Bermuda grass
- Biddy-biddy
- Bieberstein's thistle
- Bietou
- Bifid Hemp-nettle
- Big Berry Manzanita
- Big bluestem
- Big Sagebrush
- Bigbract Verbena
- Bigleaf maple
- Bigtooth aspen
- Billygoat weed
- Birchleaf Mountain Mahogany
- Bird cherry
- Bird-in-a-bush
- Bird's foot violet
- Bird's-eye speedwell
- Bird's-foot trefoil
- Bird's-nest orchid
- Birthwort
- Biting Stonecrop
- Bitter fleabane
- Bitter Melon
- Bitter Vetch
- Bitter wintercress
- Bitternut hickory
- Bitterroot
- Bittersweet nightshade
- Bitterweed
- Black ash
- Black Bryony
- Black cherry
- Black cohosh
- Black cottonwood
- Black crowberry
- Black henbane
- Black horehound
- Black huckleberry
- Black knapweed
- Black locust
- Black maidenhair fern
- Black mangrove
- Black Medick
- Black nightshade
- Black oak
- Black Poplar
- Black raspberry
- Black sage
- Black spleenwort
- Black spruce
- Black Tupelo
- Black wattle
- Black willow
- Black-bindweed
- Black-eyed Susan
- Black-eyed Susan vine
- Blackfoot daisy
- Blackhaw
- Blackjack oak
- Blackthorn
- Blackwood
- Bladder campion
- Bladder sedge
- Bladderpod
- Bloodroot
- Bloody Crane's-bill
- Blue Bugle
- Blue cohosh
- Blue columbine
- Blue dicks
- Blue elder
- Blue Eryngo
- Blue Grama
- Blue mistflower
- Blue Pea
- Blue phlox
- Blue Pigroot
- Blue plumbago
- Blue Scarlet Pimpernel
- Blue vervain
- Blue water-speedwell
- Bluebead lily
- Bluebell
- Bluemink
- Bluestem goldenrod
- Blunt woodsia
- Boar Thistle
- Bog bilberry
- Bog cranberry
- Bog Labrador Tea
- Bog myrtle
- Bog wintergreen
- Bog Yellowcress
- Bogbean
- Bonfire moss
- Borage
- Border privet
- Bottlebrush grass
- Box elder
- Bract Disa
- Bracted Lousewort
- Branched Asphodel
- Branched Pencil Cholla
- Brass Buttons
- Brazilian pepper
- Brazilian Vervain
- Bread Wheat
- Bride's Bonnet
- Bristle thistle
- Bristly greenbrier
- Bristly haircap moss
- Bristly Mallow
- Bristly oxtongue
- Brittle bladderfern
- Brittle False Pimpernel
- Brittle Pricklypear
- Brittlebush
- Broad-leaved dock
- Broad-leaved goldenrod
- Broad-leaved helleborine
- Broad-leaved Marsh Orchid
- Broad-leaved Stonecrop
- Broad-leaved sweet pea
- Broad-leaved Violet
- Broad-winged Thistle
- Broadleaf arrowhead
- Broadleaf cattail
- Broadleaf enchanter's nightshade
- Broadleaf forget-me-not
- Broadleaf Speedwell
- Broadleaved pepperweed
- Brocade moss
- Brooklime
- Broom Snakeweed
- Brown Knapweed
- Brown Monkwort
- Brown-eyed Susan
- Brown-spined Pricklypear
- Buck's-horn Plantain
- Buckbrush
- Buckhorn Cholla
- Buffalo Gourd
- Buffalo-bur
- Buffelgrass
- Bugweed
- Bulbous Bluegrass
- Bulbous buttercup
- Bull Thistle
- Bur clover
- Bur oak
- Bur Parsley
- Burnet-saxifrage
- Burnt-tip Orchid
- Burrobush
- Bush Poppy
- Bush Vetch
- Bushgrass
- Butcher's-broom
- Butterfly bush
- Butterfly ginger lily
- Butterfly milkweed
- Butterfly pea
- Butternut
- Butterweed
- Buttonbush
- Buttonweed