Abstract
Foxtail millet (Setaria italica) and Common millet (Panicum miliaceum) are the oldest domesticated dry farming crops in Eurasia. Identifying these two millets in the archaeobotanical remains are still problematic, especially because the millet grains preserve only when charred. Phytoliths analysis provides a viable method for identifying this important crop. However, to date, the identification of millet phytoliths has been questionable, because very little study has been done on their morphometry and taxonomy. Particularly, no clear diagnostic feature has been used to distinguish between Foxtail millet and Common millet. Here we examined the anatomy and silicon structure patterns in the glumes, lemmas, and paleas from the inflorescence bracts in 27 modern plants of Foxtail millet, Common millet, and closely related grasses, using light microscopy with phase-contrast and microscopic interferometer. Our research shows that five key diagnostic characteristics in phytolith morphology can be used to distinguish Foxtail millet from Common millet based on the presence of cross-shaped type, regularly arranged papillae, Ω-undulated type, endings structures of epidermal long cell, and surface ridgy line sculpture in the former species. We have established identification criteria that, when used together, give the only reliable way of distinguishing between Foxtail millet and Common millet species based on their phytoliths characteristics, thus making a methodological contribution to phytolith research. Our findings also have important implications in the fields of plant taxonomy, agricultural archaeology, and the culture history of ancient civilizations.
Highlights
Phytoliths are microscopic silica bodies that precipitate in or between cells of living plant tissues, and are widespread in all types of plants and all their different organs and structures, from roots to culms to inflorescences [1,2,3,4]
This paper reports the first attempt to determine if phytoliths analysis of the inflorescences bracts can be an effective tool for discriminating between Foxtail millet (S. italica) and Common millet (P. miliaceum)
S. glauca (Linn.) Beauv., S. viridis (L.) Beauv., and Echinochloa crusgalli (L.) Beauv. Of these 27, four species were sampled from annotated folders at the National Crop Gene Bank of China, Chinese Academy of Agricultural Sciences (CAAS); six species were sampled from the Culture Museum of Cishan, Wuan, Hebei Province, China; fourteen species were sampled from Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing, China; and three species were sampled from East China Normal University, Shanghai, China
Summary
Phytoliths are microscopic silica bodies that precipitate in or between cells of living plant tissues, and are widespread in all types of plants and all their different organs and structures, from roots to culms to inflorescences [1,2,3,4]. Foxtail millet (Setaria italica) and Common millet ( known as Broomcorn millet, Panicum miliaceum), belong to Panicoideae of Poaceae, are considered to be dry farming cereals that form the oldest cultivated foods known to humans [14,15,16]. They were staple foods in the Far East (China, Japan, Russia, and India) and even in the entire Eurasian continent prior to the popularity of rice and wheat, and are still important foods in the semi-arid regions today [14,17,18]. The identification of millet phytoliths has been questionable [8,20,22], because very little study has been conducted on millet phytoliths, no clear diagnostic feature has been used to distinguish Foxtail millet from Common millet [8]
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