Il Vegetariano is a long-time favorite for vegetarians and vegans in Florence. Seating is communal (some smaller tables available as well) and staff are friendly. In fact, it's possible that Jerry Garcia is alive and that he works here / may own the place (or perhaps that's just Jerry's Italian cousin). This is a great place to go with omnis, as there's a lot on the menu and they always come away amazed with the food. I wish there were more vegan options, but there's always something good on the menu for me. The salad bar is also great, you can create more or less exactly what you want, and the vegan tofu dressing is delicious. You don't need a reservation (they don't take reservations, actually), so ok to rock up with as many as you can get to join your plant-based party. The outdoor seating is fun if you're seeking a chilled vibe for group discussion (heat is available outside in winter, and it's fairly cool outside in summer). Overall this is an awesome place and is highly recommended. You and your guests will enjoy good food and have a great time here.
Cons: Wish there were more vegan options