| Baccharis halimifolia | Groundsel Tree |
| Baptisia tinctoria | Yellow Wild Indigo |
| Barbarea verna | Early Yellow-rocket |
| Barbarea vulgaris | Yellow Rocket |
| Bartonia paniculata subsp. paniculata | Twining Bartonia |
| Bartonia virginica | Yellow Screwstem |
| Berberis thunbergii | Japanese Barberry |
| Bidens bipinnata | Spanish Needles |
| Bidens cernua | Nodding Tick-seed |
| Bidens comosa | Three-lobe Tick-seed |
| Bidens frondosa | Devil's Tick-seed |
| Bidens laevis | Smooth Tick-seed |
| Bidens polylepis | Tick-seed Sunflower |
| Boechera laevigata var. laevigata | Smooth Rockcress |
| Boehmeria cylindrica | False Nettle |
| Boltonia asteroides var. glastifolia | Aster-like Boltonia |
| Botrychium dissectum | Cutleaf Grapefern |
| Botrychium virginianum | Rattlesnake Fern |
| Botrypus virginianus | Rattlesnake Fern |
| Brachythecium acuminatum | Foxtail Moss |
| Brassica campestris | Bird's Rape |
| Brassica rapa | Bird's Rape |
| Brassica septiceps | Bird's Rape |
| Broussonetia papyrifera | Paper-mulberry |
| Buddleja davidii | Butterfly-bush |