- Illinois bundleflower
- Imperforate St John's-wort
- Indian fig opuntia
- Indian Heliotrope
- Indian mango
- Indian pennywort
- Indian Pokeweed
- Indian shot
- Indian tobacco
- Indian tulip tree
- Indiangrass
- Inkweed
- Intermediate wood fern
- Interrupted clubmoss
- Interrupted fern
- Irish Fleabane
- Italian arum
- Italian thistle
- Ithuriel's Spear
- Ivy gourd
- Ivy Tree
- Ivy-leaved cyclamen
- Ivy-leaved Speedwell
- Ivy-leaved toadflax