Abstract Detail

Paleobotanical Section

HERMSEN , ELIZABETH JEAN [1].

Reconstructing the fossil record of Marsilea in North America.

Marsilea is a genus of rhizomatous, heterosporous water ferns in the family Marsileaceae. It is unique amongst the extant genera of the family in having compound leaves with four reticulate-veined leaflets that appear to be in a whorl at the tip of the petiole. The macrofossil record of plants with Marsilea-type leaves is thought to extend back to the Late Cretaceous (or possibly earlier), although it has long been difficult to interpret due to scarce material and misidentifications. Almost all nineteenth and early twentieth century reports have since been called into question or transferred to other taxa, leaving two generally accepted published reports from North America. The older is Marsileaceaephyllum johnhallii (J. Skog & Dilcher) Nagalingum from the Cenomanian of the Dakota Formation, Kansas, USA. Reexamination of the type material for this taxon, however, indicates that it does not represent a marsileaceous fern. The leaves or leaflets have glandular teeth and a venation pattern that suggests that the taxon may represent an aquatic angiosperm; specifically, the material resembles the obscure species Fortuna marsilioides (Bell) McIver & Basinger that occurs in Upper Cretaceous to Paleocene sediments of western North America. The younger report, consisting of formally unnamed leaves from the Eocene Wasatch Formation of Wyoming, USA, appears to be correctly attributed to Marsileaceae. An additional suite of undescribed Marsilea-type leaves and leaflets from several localities in the middle Eocene Green River Formation, Colorado and Utah, USA, has recently been identified from several fossil collections. These are essentially identical to leaves of extant Marsilea (e.g., they have four leaflets and the leaflets have reticulate venation). Marsileaceous spores and sporocarps are not yet known from sediments that yield any of these putative Marsilea leaves, leaving critical gaps in our knowledge of the morphology of the fossil plants.

1 - Ohio University, Department Of Plant Biology, Porter Hall 401, Athens, OH, 45701, USA

Keywords:
Marsilea
Marsileaceae
Fortuna
fern
Cretaceous
Eocene
Dakota Formation
Green River Formation.

Presentation Type: Oral Paper:Papers for Sections
Session: 21
Location: Whitewater/Grove
Date: Tuesday, July 29th, 2014
Time: 8:45 AM
Number: 21002
Abstract ID:139
Candidate for Awards:None