Dr. Elizabeth Hermsen
The Environmental & Plant Biology Colloquium Series presents Dr. Elizabeth Hermsen on “How to Identify a Water Clover in Deep Time: The Fossil Record and Evolution of Marsileaceae” on Friday, Oct. 6, at 11:50 a.m. in Porter Hall 104.
Hermsen is an Assistant Professor in the Department of Environmental and Plant Biology at Ohio University.
Abstract: The Marsileaceae, or water clover family, is one of two living families of heterosporous ferns in the order Salviniales (water ferns) that have a fossil record extending to the earliest Cretaceous or earlier. Marsileaceae include amphibious to aquatic, rhizomatous ferns characterized by reduced leaves and sclerified sporocarps that enclose the spore-producing sporangia. Extant genera include Pilularia (pillwort, up to 6 species, widespread), which has leaves that lack blades; Regnellidium (monotypic, South America), which has bifoliolate compound leaves; and Marsilea (water clover, 50 or more species, widespread), which has quadrifoliolate leaves. While the fossil spore record of Marsileaceae is relatively uncontroversial, the fossil sporophyte record—represented by roots, rhizomes, foliar structures (leaves and leaflets), and sporocarps—has long been inflated with dubious reports. The simple architecture of the leaves, in particular, poses difficulties for investigators, and non-marsileaceous or unidentifiable structures have frequently been attributed to the family. My investigations into the fossil record of Marsileaceae have yielded new insights into this challenging group, including a new report of fossil Marsilea leaves and leaflets from the Eocene Green River Formation, U.S.A., and reconsideration of the identity of the Cretaceous species Marsileaceaephyllum johnhallii (Dakota Formation, Kansas), the type species of the putatively marsileaceous fossil genus Marsileaceaephyllum. Overall, the fossil sporophyte record of Marsilea and Marsileaceae is sparser than previously thought, although occurrences of leaves attributable to Marsilea and Regnellidium still indicate that these lineages had diverged by the Late Cretaceous.
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