Eucommia constans N. Sp. Fruits from Upper Cenozoic Strata of Puebla, Mexico: Morphological and Anatomical Comparison with Eucommia ulmoides Oliver

Well-preserved and abundant carbonized fruits from the Upper Cenozoic Pié de Vaca Formation, Puebla, Mexico, reveal the presence of the genus Eucommia in southern latitudes of North America during the Neogene. The fruits are samaras composed of an elongate, narrow triangular, tapering stipe and an elliptic to oval, winged, asymmetrical fruit body that contains a seed. Structurally the fruits are formed by two unequally developed carpels fused longitudinally by their margins. The carpels are distally free and form a laterally displaced notch near the apex of the fruit with stigmatic surfaces on its walls. Preserved tissues in the fossil fruit are the epidermis with specialized mounds that apparently bore a stoma on their apex and a layer of the endocarp composed of cubic cells with thickened walls, each containing a cubic crystal. Abundant laticifers are associated with the dorsal and marginal carpelary strands and form a net that overlies the endocarp, around the seed. Fruits of extant Eucommia ulmoides are compared to the fossil fruits, and tissues and laticifers equivalent to those preserved in the fossil fruits are identified. Comparison between the fruits of Pié de Vaca and other fossil fruits revealed similarity with Eucommia montana from Oligocene strata of northwestern North America. However, differences in size and shape support the recognition of a new species, Eucommia constans Magallón-Puebla et Cevallos-Ferriz for the fruits from Pié de Vaca. These fruits are currently the youngest report in America and the southernmost report worldwide for the genus. The occurrence of Eucommia in Upper Cenozoic strata of Mexico modifies previously established notions regarding the distribution in space and time of the genus.