LATEST OCCURRENCE OF THE EXTINCT GENUS CEDRELOSPERMUM (ULMACEAE) IN NORTH-AMERICA - CEDRELOSPERMUM-MANCHESTERI FROM MEXICO

Abstract

The Upper Cenozoic flora of the Pie de Vaca Formation, Puebla, Mexico, is yielding important elements that contribute to a more complete knowledge of the Tertiary floras of southern latitudes of North America. Among the most abundant plant organs in this Formation are fruits of Cedrelospermum, an extinct ulmaceous genus belonging to the subfamily Ulmoideae. The Cedrelospermum fruits are morphologically described and fruit structure is interpreted. A single specimen with preserved cells allowed some histological description. The fruits from the Pie de Vaca Formation are compared directly to fruits of Cedrelospermum species from mid-latitude North America and Europe. Differences equivalent to those between North American species are found between the fruits of Pie de Vaca and the most similar species, justifying the recognition of a new species, Cedrelospermum manchesteri Magallon-Puebla et Cevallos-Ferriz. Detached leaves from the same strata that conform morphologically to leaves of previously known species of Cedrelospermum are described and compared to leaves of Cedrelospermum and to an equivalent genus from Europe. Although it is quite likely that these leaves formed part of the same plants that produced the Cedrelospermum manchesteri fruits, they are assigned to a separate taxon, Magdalenophyllum aequilaterum Magallon-Puebla et Cevallos-Ferriz, because the two organs are not found in organic connection. The genus Cedrelospermum was previously known from North American middle Eocene-lower Oligocene strata and European Eocene-upper Miocene strata. This new report documents the persistence of the genus in southern latitudes of North America during the Neogene, and the fruit features conform to previously observed patterns of morphological change through time in the genus. The occurrence of C. manchesteri in a volcanic ash deposit supports the assumed role of Cedrelospermum plants as re-colonizers of areas disturbed by volcanic activity.