It would seem to me that when we learn the laws of Brachot, we can simply discard the modern terminology of "fruits" and "vegetables," and forget about whether a tomato is a fruit or a vegetable, or whatever. We must accept the Gemara's categories: On that which grows on a permanent tree, we say borei pri ha-etz; on that which grows on a perennial plant, we say borei pri ha-adama, etc., etc. Whether this is based on Galen or not is an interesting question, but not really relevant to the understanding of the halacha. Although I am no botanist, I don't think that "vegetable" is even used by scientists, except as a very general term to distinguish between "animal" and "vegetable." The various products that can be purchased in the produce section of the supermarket are classified as fruits (apples, oranges, tomatos, cucumbers), stems (celery, rhubarb), roots (potatos, beets), leaves (lettuce, cabbage).