Phytolith variability in Zingiberales: A tool for the reconstruction of past tropical vegetation
Reconstructing paleovegetation is an important part of understanding ancient ecosystems. Phytoliths are preserved even when other fossil evidence (pollen, macrofossils) is not, and can provide evidence for the diversity and distribution of taxa or vegetation that may otherwise have a poor fossil record. Understanding the range of morphologies within plants will help provide better paleovegetation inferences and paleoecological reconstructions. Groups such as the gingers and their relatives (Order Zingiberales) can be ecologically informative and have been used as indicators of frost-free environments. Phytolith morphology in Zingiberales was surveyed from vegetative and reproductive organs of 36 genera and all eight extant families and from the extinct taxon Spirematospermum. Druse, trough, and hat-shape phytoliths are found in vegetative organs and are diagnostic at the family level, while seed phytoliths consistently differ from vegetative material and are highly variable. Druses are produced by Cannaceae, Costaceae, Strelitziaceae, and rarely by Marantaceae. Troughs are produced by Heliconiaceae and Musaceae and the two families are distinguishable by the depth of the central concavity. Hat-shaped morphotypes are found in Lowiaceae and Marantaceae, with those of Lowiaceae being larger in size. Zingiberaceae largely produced silica sand. Marantaceae phytoliths were variable. Globular and tabular morphotypes are among the least diagnostic and are produced in some form in most families. Spirematospermum produced silica sand. Phytoliths suggest that Spirematospermum is most closely related to Zingiberaceae, and not to Musaceae. These results provide support for distinguishing between zingiberalean families. Recognition of these morphotypes in fossil phytolith assemblages can provide evidence for (sub)tropical vegetation and distinctions can be made between microhabitats such as moist, high-light forest gaps vs. shaded understory, with the potential to produce more nuanced paleovegetation reconstructions.