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Parrott, Joan [1].

Comparison of Wood Anatomical Features of Stems, Branches and Roots of Platanus occidentalis, P. mexicana and P. wrightii (Platanaceae): Implicatio.

The modern Platanaceae are represented by a single genus, Platanus, with 6-11 species native to North America, Europe, and Asia. Species are characterized by wood having exceptionally wide, tall, near-homocellular rays and opposite intervessel pitting. Fossil woods attributed to the family are common and widely distributed, with approximately twenty species having been described from the Late Cretaceous into the early Cenozoic. Nine Platanus-like specimens were found preserved at the Late Campanian age (74–76 Ma) Jose Creek Member of the McRae Formation, south-central New Mexico. The McRae specimens sort into five distinct types, largely on the basis of vessel diameter and ray dimensions. Anatomical features of these fossil wood specimens are compared to wood descriptions of modern Platanus species, with the intraspecies variability of the extant species guiding species delimitation for the fossil specimens. Ideally, descriptions of extant woods are derived from mature stem specimens because juvenile woods can vary from their mature wood counterparts, as might woods of roots and branches. By comparison, fossil woods are described from specimens, the source of which (e.g., stem, root, branch) is not always known. To assess the degree of wood feature variability among different parts of individual trees of Platanus occidentalis, P. mexicana and P. wrightii, serial sections were prepared from stem, branch and root woods. Results for the three extant species show that stem, branch and root woods exhibit different mean vessel diameters than their stem counterparts, with roots and branches having larger and smaller mean diameters, respectively. Ray ontogeny is similar among the parts. Increase in axis radius correlates with widening of rays, while subdivision of large rays contributes to a range of ray widths throughout the axis. Rays of the main stem, branches and root are of like contour within a given species. However, wider and taller rays are first observed at smaller radius in roots and branches than their stem counterparts or constitute a higher percentage of rays. Overall, better understanding of intraspecies variability of wood features for different modern Platanus species informs interpretation of fossil woods. For the McRae fossil Platanus-like woods, mean vessel diameter is a good predictor of the fossil wood source as stem, branch or root. However, ray dimension patterns did not strongly link different specimen types as representing parts of the same species. Still, the data do provide evidence of the possible range of intraspecies variability.

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Presentation Type: Oral Paper
Session: PL7, Paleobotany: Mesozoic/Cenozoic Paleobotany
Location: /
Date: Thursday, July 22nd, 2021
Time: 1:00 PM(EDT)
Number: PL7003
Abstract ID:303
Candidate for Awards:None

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