Joseph R. Thomasson

A Fossil Grass (Gramineae: Chloridoideae) from the Miocene with Kranz Anatomy

A fossil leaf fragment collected from the Ogallala Formation of northwestern Kansas exhibits features found in taxa of the modern grass subfamily Chloridoideae. These include bullet-shaped, bicellular microhairs, dumbbell-shaped silica bodies, cross-shaped suberin cells, papillae, stomata with low dome- to triangular-shaped subsidiary cells, and Kranz leaf anatomy. The leaf fragment extends the fossil record of plants that show both anatomical and external micromorphological features indicating C4 photo-synthesis back to the Miocene. On the basis of associated mammals, the leaf fragment is assigned a Hemphillian age (7 to 5 million years ago).

Epidermal Patterns of the Lemma in Some Fossil and Living Grasses and Their Phylogenetic Significance

Morphological study of fossil grass anthoecia of Berriochloa and Nassella collected from Miocene-Pliocene strata in Kansas has revealed well-preserved epidermal structure. This seems to be the first micromorphological information known from fossil grass floral bracts. The epidermal pattern on the lemma in the fossils and their living counterparts are evidence in support of the view that the North American species of Stipa of the section Hesperostipa Elias and species of Piptochaetium have a common ancestry in Berriochloa, and that species of both taxa have been distinct from species of the Nassella, Oryzopsis, and other Stipa since at least the Miocene or Pliocene.

Diversity in leaf anatomy, and stomatal distribution and conductance, between salt marsh and freshwater species in the C4 genus Spartina (Poaceae)

Leaf anatomy, stomatal density, and leaf conductance were studied in 10 species of Spartina (Poaceae) from low versus high salt marsh, and freshwater habitats. Internal structure, external morphology, cuticle structure, and stomatal densities were studied with light and electron microscopy. Functional significance of leaf structure was examined by measures of CO(2) uptake and stomatal distributions. All species have Kranz anatomy and C(4)delta(13)C values. Freshwater species have thin leaves with small ridges on adaxial sides and stomata on both adaxial and abaxial sides. By contrast, salt marsh species have thick leaves with very pronounced ridges on the adaxial side and stomata located almost exclusively on adaxial leaf surfaces. Salt marsh species also have a thicker cuticle on the abaxial than on the adaxial side of leaves, and CO(2) uptake during photosynthesis is restricted to the adaxial leaf surface. Salt marsh species are adapted to controlling water loss by having stomata in leaf furrows on the adaxial side, which increases the boundary layer, and by having large leaf ridges that fit together as the leaf rolls during water stress. Differences in structural-functional features of photosynthesis in Spartina species are suggested to be related to adaptations to saline environments.

BERRIOCHLOA GABELI AND BERRIOCHLOA HULETTI (GRAMINEAE: STIPEAE), TWO NEW GRASS SPECIES FROM THE LATE MIOCENE ASH HOLLOW FORMATION OF NEBRASKA AND KANSAS

Abstract Berriochloa gabeli n. sp. and Berriochloa huletti n. sp. are described from fossil anthoecia (husks) recovered in late Miocene (Ash Hollow Formation) sediments in central Nebraska and central and western Kansas. Comparisons with other known fossil and living grasses suggest relationships with members of the grass tribe Stipeae and previously described B. intermedia Elias, 1942 from Ash Hollow deposits in north-central Kansas. Berriochloa gabeli and B. huletti were recovered in direct association with, or in the close vicinity, of rich biotas that provide evidence of widespread, probably treeless, grasslands with adjacent moist riparian habitats along streams or around temporary pools of water during deposition. Fossil vertebrates associated with the grasses at some sites suggest that the age of B. gabeli and B. huletti is early to middle Hemphillian.

A Comparison of CPD (Critical Point Drying) and HMDS (Hexamethyldisilazane) in the Preparation of Corallorhiza spp. Rhizomes and Associated Mycorrhizae for SEM (Scanning Electron Microscopy)

Rhizomes of Corallorhiza maculata and Corallorhiza striata and associated mycorrhizal fungi were dried with critical point drying (CPD) and air drying from hexamethy ldisilazane (HMDS) to compare the effectiveness of both methods in preparing specimens for scanning electron microscopy. Drying artifacts such as collapsed cells and lines and ridges on rhizome epidermal cells due to shrinkage resulted from both methods, but CPD produced the least artifacts. CPD and HMDS drying were equally effective at producing good to excellent preservation of internal features of the rhizomes and associated fungi with minimal artifacts.

ELEOFIMBRIS SVENSONII (CY PERACEAE) FROM THE LATE MIOCENE OGALLALA GROUP OF WESTERN KANSAS

Abstract More than 60 fossil achenes of Eleofimbris svensonii (Cyperaceae) were recovered from strata in Scott County, Kansas tentatively assigned to the late Miocene Ash Hollow Formation. This collection extends the temporal range of the taxon in this formation more than 130 km west and 20 km south and more than doubles the number of specimens available for study.