Chronology of ancient Dongxiang wild rice (Oryza rufipogon Griff.), and the morphologies of grains, double-peaked phytoliths, and starch, in the middle Yangtze river region, China

Abstract

Common wild rice (Oryza rufipogon), the ancestor of Asian domesticated rice (Oryza sative), is used as a comparator for identifying Oryza species in archaeological records. However, little attention has been paid to the characteristics of the grain morphology, double-peaked phytoliths and starch granules in ancient wild rice. Dongxiang wild rice is believed to be the current northernmost extent of wild Oryza in Asia, but few studies have been reported on the history of its growth in Dongxiang. A stratigraphic, chronological analysis of the ancient wild rice remains discovered in the sediment core at the Anjiashan in situ conservation (ISC) site in Dongxiang proves that wild rice may have been present in Dongxiang since at least 500–300cal. BP, which includes the period of climatic variations commonly called the “Little Ice Age”. Furthermore, based on a comparison between ancient and modern wild rice, as well as some indica (Huixiang 9126), japonica (Bijing 37) cultivars, it is demonstrated that the grain size of wild rice, in contrast to the double-peaked phytolith and starch granule parameters, changed little during the “Little Ice Age” of the Ming and Qing Dynasties in China, and that in terms of grain shape analysis wild rice is easily confused with indica. This may be one of the reasons why traditional grain shape and grain size analysis usually does not work well in classifying the Oryza species, and why some rice remains from archaeological sites were mainly indica as judged from their shapes but japonica in terms of their morphological parameters of double-peaked phytoliths and spikelets. Our findings may not only assist in elucidating the spatiotemporal distribution of wild rice, but can also provide important reference parameters for the identification of Oryza species in archaeological records.