Morphological characteristics of seed starch granules of Fagaceae in South China and their implication in paleodiet

Abstract

Nut fruits likely played a significant role before and during the origin of agriculture; however, relatively little research conducted on the morphological characteristics and statistical comparisons of nut fruit starch granule hinders the progress of paleodietary analysis of prehistorical society. For better species identification of starch granule remaining on tools discovered at archaeological sites, it is desirable to develop a more abundant morphology database of modern nut fruit starch granules as well as the establishment of relevant identification standards. Therefore, nuts from 40 species in four genera (Quercus, Lithocarpus, Castanea, and Castanopsis) of Fagaceae were collected from South China for statistical measurement and comparative analysis. Starch granules are highly accumulated in 34 species except for 6 species, whose shapes involve oval, subcircular, drop-shaped, rounded triangle, polygonal, spherical caps, and bell-shaped types, or a combination of several types, and the average length is between 10 and 20 μm. According to research on Quercus phylogeny relationships, it was found that the species in the same infragenious section produce similar morphological characteristics of starch granules. The result was applied in the identification of starch granules extracted from stone tools from the 20 to 10 ka cultural layer of Xiaodong Rockshelter, and some starch granules can be recognized to species level, revealing that nuts from Quercus and Lithocarpus were gathered and exploited by ancient people. This expansion of modern starch presentation and comparison of nuts helps to improve the accuracy of the identification of ancient starch and deepen the understanding of plant utilization of ancient humans.

Keywords: Quercus; South China; morphological characteristics; nut fruits; starch granule.

Figure 1

Sampling spots of specimens used in this study (1: Quercus kiukiangensis; 2: Quercus lamellosa; 3: Lithocarpus dealbatus; 4: Quercus schottkyana, Quercus variabilis, Quercus serrata, Quercus aliena, Lithocarpus elizabethiae, Castanea seguinii, Castanopsis orthacantha; 5: Lithocarpus craibianus; 6: Quercus longispica; 7: Quercus rex; 8: Lithocarpus mairei; 9: Quercus franchetii; 10: Quercus cocciferoides; 11: Quercus argyrotricha; 12: Lithocarpus gymnocarpus; 13: Lithocarpus pachylepis; 14: Quercus augustinii, Lithocarpus xylocarpus; 15: Quercus marlipoensis, Lithocarpus balansae, Lithocarpus c.f. annamitorus, Lithocarpus bacgiangensis, Lithocarpus longinux, Lithocarpus sp.1; 16: Quercus patelliformis, Lithocarpus longipedicellatus; 17: Quercus fleuryi, Lithocarpus fenzelianus; 18: Lithocarpus sp.2; 19: Lithocarpus longanoides; 20: Quercus blakei, Quercus phanera, Quercus kouangsiensis; 21: Quercus litseoides, Quercus sessilifolia; 22: Lithocarpus skanianus; 23: Quercus gilva).

Figure 2

Scanning electron micrographs of starch granule in nuts of 34 species from Fagaceae. 1, Quercus blakei; 2, Quercus argyrotricha; 3, Quercus augustinii; 4, Quercus litseoides; 5, Quercus kouangsiensis; 6, Quercus fleuryi; 7, Quercus lamellosa; 8, Quercus serrata; 9, Quercus sessilifolia; 10, Quercus gilva; 11, Lithocarpus elizabethiae; 12, Quercus kiukiangensis; 13, Quercus schottkyana; 14, Lithocarpus pachylepis; 15, Lithocarpus longipedicellatus; 16, Lithocarpus sp.; 17, Lithocarpus xylocarpus; 18, Lithocarpus fenzelianus; 19, Quercus longispica; 20, Quercus marlipoensis; 21, Castanea seguinii; 22, Quercus cocciferoides; 23, Quercus franchetii; 24, Quercus phanera; 25, Quercus aliena; 26, Quercus variabilis; 27, Lithocarpus craibianus; 28, Lithocarpus longanoides; 29, Lithocarpus mairei; 30, Lithocarpus balansae; 31, Castanopsis orthacantha; 32, Lithocarpus skanianus; 33, Lithocarpus dealbatus; 34, Lithocarpus longinux.

Figure 3

Box plot of the granule sizes of the starches examined.

Figure 4

Morphological graphs of 34 species from Fagaceae. Scale bar, 20 μm. (a, brightfield light; b, cross-polarized light). 1, Quercus blakei; 2, Quercus argyrotricha; 3, Quercus augustinii; 4, Quercus litseoides; 5, Quercus kouangsiensis; 6, Quercus fleuryi; 7, Quercus lamellosa; 8, Quercus serrata; 9, Quercus sessilifolia; 10, Lithocarpus fenzelianus; 11, Quercus gilva; 12, Lithocarpus elizabethiae; 13, Lithocarpus pachylepis; 14, Lithocarpus sp.; 15, Lithocarpus longipedicellatus; 16, Lithocarpus xylocarpus; 17, Quercus kiukiangensis; 18, Quercus schottkyana; 19, Quercus longispica; 20, Castanea seguinii; 21, Quercus marlipoensis; 22, Quercus cocciferoides; 23, Quercus franchetii; 24, Quercus phanera; 25, Quercus aliena; 26, Quercus variabilis; 27, Lithocarpus craibianus; 28, Lithocarpus longanoides; 29, Lithocarpus mairei; 30, Castanopsis orthacantha; 31, Lithocarpus balansae; 32, Lithocarpus skanianus; 33, Lithocarpus dealbatus; 34, Lithocarpus longinux.

Figure 5

Box plot of the granule sizes of plant materials used for morphological analysis based on phylogeny in this study.

Figure 6

Morphological graphs of starch granules found in the Xiaodong site. Scale bar, 20 μm (a, brightfield light; b, cross-polarized light). (A), ancient starch consistent with Lithocarpus mairei; (B), ancient starch consistent with Quercus serrata; (C), ancient starch consistent with Quercus variabilis and Quercus aliena.