THE MIDDLE EOCENE PRINCETON CHERT FLORA: THE MONOCOTS

The Middle Eocene Princeton Chert locality (Allenby Fm) is well understood, with ferns, fungi, conifers, dicots, and monocots known from this site. Monocots are rarely preserved in the fossil record, due partly to their occurrence in ephemeral habitats, and partly to their often herbaceous habit. Given this, when any fossil monocots are found they have the potential to greatly contribute to our understanding of this group. Specimens from the Princeton Chert have exceptional cellular detail preserved, allowing for detailed anatomical descriptions of taxa, and in some cases whole-plant reconstructions. Thus the Princeton Chert material offers us a unique opportunity to look at fossil moncots. To date, five monocots have been formally described from this locality: stems with attached leaves and roots of Soleredera rhizomorpha (Liliales) and Ethela sargantiana (Cyperaceae/Juncaceae); a coryphoid palm, Uhlia allenbyensis (Arecaceae), known from stems with attached leaves and roots; petioles of Heleophyton helobiaeoides (Alismataceae); and seeds of Keratosperma allenbyense (Araceae). In addition, there are several undescribed taxa: flowers and fruits with affinities to Aponogetonaceae and Potamogetonaceae (Alismatales), and two types of rhizomes that have yet to be allied with any living group. Many of the extant taxa in these groups have a preference for aquatic habitats, and the anatomical characters of the fossils support the idea that the Princeton Chert represents an in situ aquatic depositional environment. The preservation of herbaceous monocots among the plant diversity preserved by the Princeton Chert shows a unique aspect often absent from palaeoecosystems, and helps to provide a clear picture of this Middle Eocene wetland.