Infructescences from the Cerro del Pueblo Formation (Late Campanian), Coahuila, and El Cien Formation (Oligocene-Miocene), Baja California Sur, Mexico

Fruits and infructescences of the Cerro del Pueblo and El Cien Formations, Coahuila and Baja California Sur, Mexico, respectively, allow detailed description and comparison of reproductive structures of plants that grew from the Late Cretaceous at least up to the Miocene. Infructescences collected in the Rincón Colorado and Presa San Antonio localities resemble those of some members of Alismatales; they share multiple or aggregate infructescences, with sessile, unilocular, operculate berrylike fruits, that are free from one another in their distal zones and contain a single orthotropous ovule. Nevertheless, they have other characteristics not found in either fossil or extant infructescences, limiting this resemblance. These features include the development of a distal seed crown by integumentary projection, a fruit operculum inserted into the seed crown, and a channel running through the mesocarp from the exposed operculum surface to the proximal end of the fruit. The presence of sclerotized layers in the seed suggests that the reproductive organs are mature. Differences in number of fruits per infructescence, seed form, number of integumentary layers, and cell sizes in the seed and fruit suggest that two related species are represented among the ca. 1283 known infructescences. This suggests that during the Cretaceous diversity within the order was important. The only infructescence collected from the Oligocene-Miocene El Cien Formation has a morphology that closely resembles that of the Cretaceous material. Even the polyhedric shape of the exocarp cells of the Baja California Sur material is similar to that of the Coahuila material. Unfortunately, this material was not cut for further comparison, but the available data suggest that this lineage lived in northern Mexico until at least the Oligocene-Miocene.