Abstract Detail



Paleobotany

Manchester, Steven [1], Spielbauer, Robert [2], Huegele, Indah [2].

Platanus dissecta leaves in association with unusually large infructescences from the Miocene of western North America.

Leaves of Platanus are common and readily recognized in Miocene floras of western North America, but different philosophies have been used to distinguish species among the fossil occurrences, and their systematic and biogeographic relationships to modern species of Platanus have been uncertain.  We reviewed Miocene collections from California, Oregon, Washington, and Idaho and consider them to represent a single widespread species, for which the name with priority is Platanus dissecta Lesquereux.  Petioles are variable in length and have a markedly enlarged, hollow base indicating that they enveloped the axillary bud, as in all extant species of Platanus subg. Platanus.  The laminae range from ovate-unlobed to 5-lobed, but are usually trilobate with well-incised sinuses and palinactinodromous venation.  Leaf blades and stipules are serrate, typically with widely spaced teeth and rounded sinuses. Epidermal anatomy, examined by epifluorescence microscopy on specimens from the Latah flora of Idaho, shows anomocytic stomata and multicellular trichome bases in conformity with extant species.  Reproductive structures have not previously been documented for Platanaus dissecta.  Although not found at the type locality of the species, inflorescences and infructescences associate with the leaves at the Sucker Creek flora, Oregon, and isolated achenes are known from Emerald Creek flora, Idaho. Mature infructescence heads were ca 15 mm in diameter with 5-7 achenes per floret.  Dispersal hairs arise from the base of each achene. An interesting feature of the infructescences is their gigantism relative to all modern species of Platanus. Although available specimens are all incomplete (broken at both ends), judging from the unusually thick raceme axes (2.5 to 4.9 mm compared to a maximum 2.3 mm in extant species), the spacing of fruiting heads over the preserved portion, and the standard taper rate of an axis, we estimate that P. dissecta, racemes were at least 42 cm long and bore 20 or more capitula.  Modern species of Platanus subgenus Platanus rarely exceed 15 cm and bear just 1 to 8 capitula.  


1 - Florida Museum of Natural History, University of Florida, Dickinson Hall, 1659 Museum Rd, Gainesville, FL, 32611-7800, United States
2 - University of Florida, Florida Museum of Natural History, Dickinson Hall, 1659 Museum Rd, Gainesville, FL, 32611-7800, United States

Keywords:
fossil
Miocene
Platanaceae.

Presentation Type: Oral Paper
Number:
Abstract ID:559
Candidate for Awards:None


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