Perezia nana.
Botanical name:
Perezia (Acourtia) nana, Gray (natural size). - 1. Corolla. 2. Stamens. 3. Akene (magnified). 4. Floret (natural size).
This image is from the article "On the Presence of Pipitzahoic Acid in the Perezias ..." in the American Journal of Pharmacy, 1884.