Chen Iju, Li Kuang-Ti, Tsang Cheng-Hwa
Archaeology Department, Institute of History and Philology, Academia Sinica, No. 130, Section 2, Academia Rd., Nangang District, Taipei, 115, Taiwan.
Bot Stud. 2020 Mar 2;61(1):5. doi: 10.1186/s40529-020-0282-x.
Grass phytoliths are the most common phytoliths in sediments; recognizing grass phytolith types is important when using phytoliths as a tool to reconstruct paleoenvironments. Grass bulliform cells may be silicified to large size parallelepipedal or cuneiform shaped phytoliths, which were often regarded as of no taxonomic value. However, studies in eastern Asia had identified several forms of grass bulliform phytoliths, including rice bulliform phytolith, a phytolith type frequently used to track the history of rice domestication. Identification with a higher level of taxonomic resolution is possible, yet a systematic investigation on morphology of Poaceae bulliform phytoliths is lacking. We aimed at providing a morphological description of bulliform phytoliths of Poaceae from Taiwan based on morphometric measurements in anatomical aspect. The results are important references for paleo-ecological studies.
The morphology of grass bulliform phytoliths is usually consistent within a subfamily; the end profile is relatively rectangular in Panicoideae and Micrairoideae, whereas cuneiform to nearly circular in Oryzoideae, Bambusoideae, Arundinoideae, and Chloridoideae. Bulliform phytoliths were seldom observed in Pooideae. Certain morphotypes are limited to plants growing in specific environments. For example, large, thin, and pointed bulliform phytoliths are associated with wet habitat; Chloridoideae types are mostly from C4 plants occupying open arid places.
Grass bulliform phytoliths can be identified at least to the subfamily level, and several forms were distinguished within large subfamilies. Previously un-reported silicified cell types, i.e., arm cells and fusoids, and two special trichome phytolith types associated with bulliform phytoliths, were described. Morphometric methods were great tools for delimiting morphotypes; with refined morphological classification the association between forms and habit/habitats was revealed. The knowledge provides new ways to interpret phytolith assemblage data, and it is especially useful when the sediments are enriched in large blocky phytoliths.
禾本科植物硅酸体是沉积物中最常见的硅酸体；在将硅酸体用作重建古环境的工具时，识别禾本科植物硅酸体类型很重要。禾本科植物泡状细胞可能被硅化形成大型平行六面体或楔形硅酸体，这些硅酸体通常被认为没有分类学价值。然而，东亚的研究已经识别出几种禾本科植物泡状硅酸体形式，包括水稻泡状硅酸体，这是一种经常用于追踪水稻驯化历史的硅酸体类型。虽然有可能实现更高分类分辨率的识别，但目前缺乏对禾本科植物泡状硅酸体形态的系统研究。我们旨在基于解剖学方面的形态测量，对台湾禾本科植物泡状硅酸体进行形态描述。研究结果为古生态研究提供了重要参考。
禾本科植物泡状硅酸体的形态在一个亚科内通常是一致的；黍亚科和类蜀黍亚科的端面轮廓相对呈矩形，而在稻亚科、竹亚科、芦竹亚科和虎尾草亚科中则呈楔形至近圆形。早熟禾亚科很少观察到泡状硅酸体。某些形态型仅限于生长在特定环境中的植物。例如，大型、薄且尖的泡状硅酸体与湿润生境相关；虎尾草亚科类型大多来自占据开阔干旱地区的C4植物。
禾本科植物泡状硅酸体至少可以鉴定到亚科水平，并且在大型亚科内区分出了几种形式。描述了以前未报道的硅化细胞类型，即臂细胞和纺锤体，以及与泡状硅酸体相关的两种特殊毛状体硅酸体类型。形态测量方法是划分形态型的有力工具；通过精细的形态分类揭示了形态与习性/生境之间的关联。这些知识为解释硅酸体组合数据提供了新方法，在沉积物中富含大型块状硅酸体时尤其有用。
