A New Genus and Species of Grass, Eograminis balticus (Poaceae: Arundinoideae), in Baltic Amber

Abstract

Premise of research. This investigation was undertaken to describe a multifloral grass spikelet enclosed in Baltic amber. The fossil, described in the new genus Eograminis, represents the first definite grass to be described from Baltic amber as well as the first fossil member of the subfamily Arundinoideae. The discovery adds a new plant group to the extensive flora previously described from Baltic amber and provides insights into the ecology of the forest habitat. It also supplies morphological and developmental features that existed in early Cenozoic grasses and establishes a calibration point for future phylogenetic studies regarding the origin and splitting of genera in the subtribe Moliniinae. Methodology. The piece of amber containing the fossil was reshaped with a diamond blade lapidary trim saw, a belt sander, and a bench polisher until it was possible to view the grass spikelet from all angles. Because of the excellent preservation of the spikelet, observations of the glumes, paleae, and lemmas could be made under direct light with a stereoscopic and compound microscope. Pivotal results. After the features of the spikelet are characterized, it is described as Eograminis balticus gen. et sp. nov. (Poaceae: Arundinoideae). The new genus is characterized by the presence of stomata with well-developed dome-shaped subsidiary cells, parallel guard cells, and rows of crenulated and noncrenulated epidermal cells with long and short cells and silica bodies. Conclusions. The spikelet has some features of members of the extant genus Molinia Schrank in the tribe Molinieae, subtribe Moliniinae, a wetland genus with extant species concentrated around the Baltic Sea. However, the sparse scabrosity over the lemma veins, minute or absent keel hooks on the paleae, and bicellular or absent microhairs of Molinia spp. separate it from the fossil. The presence of an immature orthopteran and an "Alternaria-like fungal spore" associated with the fossil grass provides data on the microhabitat of the fossil grass.