There are around 30 species of Porophyllum, the majority of which are found in Mexico and southward. Around me in the borderlands of Arizona Sonora there are 2 species; yerba de venado or Porophyllum gracile, a perennial and P. ruderale, the annual version jabbered about in this episode of Growing Native.
Porophyllum ruderale var. macrocephalon has quite a range from the mesas and mountains near me and southward to South America. That explains why one of the common names for this plant is Bolivian cilantro. Oh, and that’s only one of the common names (there are many, as it does cross a lot of borders!), here are a couple more: yerba porosa or pápalo. Now you know.
The photos are mine of the plant with dry seed heads on a rocky slope in the Galiuro Mountains.