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

The Upper Cenozoic flora of the Pie de Vaca Formation, Puebla, Mexico, is yielding important elements that contribute to a more complete kno wledge of the Tertiary floras of southern latitudes of North America. Among the most abundant plant organs in this Formation are fruits of C edrelospermum, an extinct ulmaceous genus belonging to the subfamily U lmoideae. 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 Vac a 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 P ie 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 morphologic ally to leaves of previously known species of Cedrelospermum are descr ibed and compared to leaves of Cedrelospermum and to an equivalent gen us from Europe. Although it is quite likely that these leaves formed p art of the same plants that produced the Cedrelospermum manchesteri fr uits, they are assigned to a separate taxon, Magdalenophyllum aequilat erum Magallon-Puebla et Cevallos-Ferriz, because the two organs are no t found in organic connection. The genus Cedrelospermum was previously known from North American middle Eocene-lower Oligocene strata and Eu ropean Eocene-upper Miocene strata. This new report documents the pers istence of the genus in southern latitudes of North America during the Neogene, and the fruit features conform to previously observed patter ns of morphological change through time in the genus. The occurrence o f C. manchesteri in a volcanic ash deposit supports the assumed role o f Cedrelospermum plants as re-colonizers of areas disturbed by volcani c activity.