When I posted the pic of the Red Porterweed two days ago, I didn't give the botanical name. I'll try to clarify the porterweeds and their kin.
Stachytarpheta mutabilis = Red Porterweed is a tropical plant from South America. The Red is similar in growth habit to Stachytarpheta urticifolia the Blue Porterweed that I grow.
Stachytarpheta urticifolia -- the name gives a clue that the leaves might make our skin itch. Both the red and blue Porterweeds are tropicals, not reliably hardy in my zone 8 garden. Mine came originally from a plantation butterfly garden nearby and I keep cuttings over the winter. When I took the pic of the porterweed this morning, a cool wind was blowing and the butterflies were hanging around Tithonia in sunnier parts of the garden.
Stachytarpheta jamaicensis, or Jamaica Porterweed is considered a south Florida native, but some believe it came to Florida with Bahamian settlers who brought seeds of medicianal plants with them. It is a lower, more spreading grower than the others, also with blue flowers.
Frequently seen in southern states is Blue Vervain, or Veberan hastata. This plant is sometimes called Swamp Verbena, or wild Hyssop. Butterflies flock to it in wild areas. More about Blue Vervain at Clemson Extension