STULTS, DEBRA Z , AXSMITH , BRIAN J .
New observations on the last Pterocarya occurrences in North America.
Pterocarya is a genus of the Juglandaceae that was once widespread throughout much of the North Hemisphere but is now restricted to the Caucasus region and eastern Asia. This study provides new details regarding Pterocarya macrofossils from the Late Neogene of eastern North America, which include the last known occurrences of this taxon on the continent. Abundant eroded nutlets with missing wings are known from the Late Miocene Brandywine flora of Maryland, but re-examination of collections from this site have revealed six nutlets with the wings still intact. The wings are semi-orbicular, similar in shape to the extant Japanese species Pterocarya rhoifolia. Bisected endocarps display the cusp-like projection on either side of a secondary septum as found in Pterocarya rhoifolia and Pterocarya macroptera (section Platyptera), but not occurring in other extant species of Pterocarya (section Pterocarya). Contrastingly, only one Pterocarya fruit has been identified from the Late Pliocene Citronelle Formation in southern Alabama thus far. Two Pterocarya leaflets have also been identified. This, along with the absence of Pterocarya pollen, indicates that the genus was rare in southeastern North American by the Late Pliocene. At 1.2 cm in diameter, the Citronelle Pterocarya nutlet is the largest recorded for the genus, including all known fossil and extant forms. Based on a comprehensive review of the genus, it is remarkable that this fruit has the smallest wing/nutlet area ratio. The wing shape is semi-orbicular; however, unusually prominent veins anastomose forming a strong supporting network in contrast to the subparallel venation pattern typical of other Pterocarya fruit wings. In other words, cross veins of the wings are often as prominent as the lateral veins, which may be relatable to the large nutlet. This unusually large nutlet combined with the relatively small wing area in this last North American Pterocarya fruit record may indicate that the genus was undergoing an ultimately unsuccessful transition from wind to animal dispersal.
1 - University Of South Alabama, University Of South Alabama, Biology Department, 5871 USA Drive North, Room 124, Mobile, AL, 36688
2 - University Of South Alabama, Biology Department, 5871 USA Drive North, Room 124, MOBILE, AL, 36688-0002, USA
Presentation Type: Oral Paper:Papers for Sections
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