Calciphytoliths (calcium oxalate crystals) analysis for the identification of decayed tea plants (Camellia sinensis L.)

Abstract

The history of tea is poorly known, mainly due to the questionable identification of decayed tea plants in archaeological samples. This paper attempts to test the utility of calciphytoliths (calcium oxalate crystals) for the identification of tea in archaeological samples. It provides the first survey of the macropatterns of calciphytoliths in several species of Theaceae and common non-Theaceae plants. Crystals were extracted from 45 samples of tea, Theaceae and common non-Theaceae plants, and detected microscopically between crossed polarizers. In tea plants, druse and trichome base are the most distinctive crystals. Druses have the smallest diameter (11.65 ± 3.64 μm), and trichome bases have four distinctive straight and regular cracks, similar to a regular extinction cross. The results provide morphological criteria for distinguishing tea from other plants, specifically the presence of identifiable druses together with calcified trichome bases. The implications are significant for understanding the history of tea and plant exploitation, especially for plants for which the preservation of macrofossils is poor.

Earliest tea as evidence for one branch of the Silk Road across the Tibetan Plateau

“…However, no diagnostic morphological features survive that can be used to identify unequivocally these partially decayed leaves and buds as tea. Recently, the development of biomarker and calcium phytolith proxies has allowed the identification of components from decayed food and tea remains 2 13 18 19 . Further, a recent study has used both theanine and caffeine markers as a basis for tea identification 5 20 .…”

“…The Tibetan Plateau was then closely linked eastwards to central China through trade of tea and horses for Tibetan furs and medicinal plants 6 7 8 9 10 . Although trade of millets already connected the Tibetan Plateau to lowland China more than 4000 calibrated years before present (yr BP) 11 , and barley cultivation and pastoralism expanded after 3600 yr BP 12 , the emergence of historical patterns of commodity trade and habits of tea drinking along the Silk Road and in the Tibetan Plateau has remained poorly understood, due mainly to the poor preservation of plant leaves, and the challenge of identifying decayed tea remains in archeological samples 7 13 .…”

“…1a ). Large modern reference collections are used to compare and contrast microfossil morphology and biomolecular components of these ancient remains to modern standards of tea and related plant species 13 . Our study reveals that tea was drunk by Han Dynasty emperors as early as 2100 yr BP and had been introduced into the Tibetan Plateau by 1800 yr BP.…”

Anatomical Study and Characterization of Metabolites in Leaves of Momordica charantia L.

“…30 The analysis of the slides was conducted using a polarized microscope (Leica DM750M) coupled with a digital camera (Leica ICC50 W), through images processed in software (LAS EZ).…”

Occurrence and variation of calcium oxalate crystals in selected medicinal plant species

“…CaOx crystals are more common in leaves than in stems (Meric 2009a) and are often found in the epidermal, mesophyll and vascular tissues (He et al 2011). The common CaOx crystal types based on morphology are the raphides, druses, prismatic crystals, styloids and crystal sands (Ilarsan et al 1997, Zhang et al 2014.…”