Phytolith Morphology Research Articles

Revised taxonomic interpretations of Cyperaceae phytoliths for (paleo)botanical studies with some notes on terminology

This paper comprises two complementary parts. Firstly, phytolith morphology results from 17 species in 8 genera (Cyperus, Eleocharis, Fuirena, “Mariscus,” “Pycreus,” “Schoenoxiphium,” Scirpoides and Scleria) that were drawn from phytolith analysis of 36 sedge species from 13 genera are presented for their importance in the taxonomically problematic Cyperaceae. Secondly, we provide a synthesis aimed at bridging the current disconnect between phytolith analyses in paleobotanical studies and botanical studies which also seem to recognize plant silica differently. We found that results which were thought to be novel for paleobotanical studies have already been documented by taxonomists. To this end, commonly used terms such as “Cyperus/Kyllinga-type” and “Scirpus-type” in paleobotanical studies are not consistent with sedge taxonomy and need to be revised to adapt to new sedge classifications. We present supporting phytolith morphology evidence. We report likely the first known evidence of the presence of the Carex-type phytolith morphotype in the African genus “Schoenoxiphium.” Among others, our phytolith data support the generic classification of Scleria and provides tentative support for the recent suggested close relationship between Fuirena and Eleocharis by molecular studies. Although this study is limited in scope and the fact that the presence of the same unique morphotype in different taxa does not necessarily imply that they are closely related since they may exhibit homoplasy, our data are a preliminary step on how phytolith morphology may contribute to understanding relationships in Cyperaceae, a character that has long been used by taxonomists.

Silicon variation and phytolith morphology in different organs of Dendrocalamus brandisii (Munro) Kurz (Bambusoideae)

Silicon is an essential element for the growth and development of bamboo plants that significantly affects the biochemical and physical properties for industrialized bamboo utilization. Silicon is biomineralized as diverse forms of phytoliths in the bamboo organs. We investigated the silicon variation and phytolith morphology in different organs of Dendrocalamus brandisii (Munro) Kurz. The silicon content in D. brandisii (Munro) Kurz varies and increases in the order of leaf > sheath > branch > culm > shoot > root. The phytolith morphotypes and presence frequency in different D. brandisii organs varied closely interrelated with the cell structure and organ functions. Amorphous silicon deposition and few varieties and numbers of phytolith were found in D. brandisii root and shoots. Rich distribution of the saddle and dumb-bell phytoliths was found in all organs except the root and mature culm and branch. More elongate and rectangular phytoliths were found in mature culm and branch. Round and elliptical phytoliths might be firstly formed followed by dumb-bell and saddle phytoliths. Phytolith sizes increased with increasing culm, branch and leaf age, but did not demonstrate a specific trend with culm height. The result could contribute to enriching phytolith morphology in Gramineae and provide theoretical basis and references for plant taxonomy and large-scale bamboo industrial processing and utilization.

Prehistoric agricultural transformations in tropical Remote Oceania: Towards comprehensive phytolith analysis

In Micronesia, and more broadly in the Pacific Islands, human-introduced plants, especially vegetatively-propagated root/tuber and tree crops, form a large part of local diets. Archaeobotanists working in the region often employ phytolith analysis to understand the landscapes these plants help create, the role that they play in human migration and settlement, and socio-cultural aspects of food production systems. However, to more fully understand the benefits and limitations of this method, it is necessary to develop and analyze regional, archaeologically-oriented phytolith reference collections, as has been done in other regions of the world. This paper presents an analysis of one such reference collection to more fully understand the potential and limitations of phytolith analysis in the archaeology of the Pacific Islands, specifically oriented towards the island of Pohnpei, Micronesia. In this analysis, 77 plant taxa were processed, individual phytolith morphologies were recorded, and plants and plant parts were categorized according to phytolith production. Results confirm that phytoliths in the taxa of this region are abundant and specific, and can be used for both understanding landscape use and the function of artifacts and features. However, there are some notable limitations that may be specific to the Pacific region and the crops that grow here.

Physiological and anatomical response of foliar silicon application to Dendrocalamus brandisii plantlet leaves under chilling

The physiological and anatomical responses of different concentrations (0.0, 0.5, 1.0, 2.0 and 4.0 mM sodium silicate) of Si foliar-application in improving the chilling tolerance of Dendrocalamus brandisii plantlets were investigated. The Si-supplemented D. brandisii plantlets exhibited better chilling tolerance, associated with the enhancement of photosynthetic pigment and soluble sugar and starch content, increasing CAT and SOD activities and decreasing MDA and H2O2 level, as well as thicker leaf blades and mesophyll tissues. Furthermore, distinct changes in phytolith morphology were observed, including formation of a new phytolith morphotype (dumb-bell with nodular shark), significantly higher frequency of elongated phytoliths, and the increased length of elongated and elliptical phytoliths. Results indicated the physiological and anatomical response showed weak positive linkage with increasing amount of silicon applied, and the 1.0 mM sodium silicate on D. brandisii plantlet leaves was the most effective treatment in enhancing chilling tolerance.

Observation of the transformation of silica phytoliths into SiC and SiO2 particles in biomass-derived carbons by using SEM/EDS, Raman spectroscopy, and XRD

Scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy, Raman spectroscopy, and X-ray diffraction were successfully used to observe the location and morphology of the silica phytoliths in biomass-derived carbons and their transformation into SiC and SiO2 particles at high heat treatment temperatures (HTT). The analyses were conducted in chars derived from the endocarp of babassu coconut (EBC), which naturally contains 1.6 wt% of silica in its mineral matter. It was observed that EBC chars with 500–1200 °C HTT present globular echinate SiO2 phytoliths with sizes of 12–16 μm; these phytoliths are mostly concentrated around the surface of the submillimeter char fibers and also in the carbonaceous char matrix. No phytoliths are found in the interior of the char fibers. At 1200 °C HTT, the phytoliths begin to be rounded, and above 1300 °C HTT, most phytoliths decompose and silicon reacts with carbon-forming nanocrystalline β-SiC particles (~ 35 nm crystallite size). Numerous (tens to hundreds) micro- and sub-micro-amorphous or nanostructured SiO2 particles (with sizes predominantly below 2 µm) are then observed at the sites previously occupied by the phytoliths. Few rounded phytoliths survive at 1400 °C HTT, but disappear at higher HTTs (1600–2000 °C). It is likely that the ensembles of micro- and sub-micro-SiO2 particles observed in many sites correspond to the inner remaining part of the original phytoliths, whose most external SiO2 structures (at and near the surface) decompose and take part in the carbothermal reaction for the formation of SiC.

Microparticles of Silica (Phytoliths) Found in <i>Cannabis sativa</i> from Khabarovsky Krai (Russia)

First data on morphology of phytoliths was obtained for leaves, body, and inflorescence of Cannabis sativa found in 2 regions of the Khabarovsky region (Khabarovsk City and Bikinsky District). Optical microscopy revealed 5 phytoliths morphotypes in the scape, inflorescence, and in the leaves of the cannabis: shapeless, oval, segmented oval, club-shaped, and spikes. Size of phytoliths from various plant’s parts is found to be uniform, but their morphometry changes with respect to ratio among shapes. Shapeless dominate in the scape (68%), inflorescence, and in leaves (31.33%). Spikes are found in inflorescence (32%) as well as in scape (30%) and in leaves (10.6%).

Effects of lanthanum and acid rain stress on the bio-sequestration of lanthanum in phytoliths in germinated rice seeds.

REEs in the environment can be absorbed by plants and sequestered by plant phytoliths. Acid rain can directly or indirectly affect plant physiological functions. Currently, the effects of REEs and acid rain on phytolith-REEs complex in plants are not yet fully understood. In this study, a high-silicon accumulation crop, rice (Oryza sativa L.), was selected as a representative of plants, and orthogonal experiments were conducted under various levels of lanthanum [La(III)] and pH. The results showed that various La(III) concentrations could significantly improve the efficiency and sequestration of phytolith La(III) in germinated rice seeds. A pH of 4.5 promoted phytolith La(III) sequestration, while a pH of 3.5 inhibited sequestration. Compared with the single treatment with La(III), the combination of La(III) and acid rain inhibited the efficiency and sequestration of phytolith La(III). Correlation analysis showed that the efficiency of phytolith La(III) sequestration had no correlation with the production of phytolith but was closely correlated with the sequestration of phytolith La(III) and the physiological changes of germinated rice seeds. Phytolith morphology was an important factor affecting phytolith La(III) sequestration in germinated rice seeds, and the effect of tubes on sequestration was more significant than that of dumbbells. This study demonstrated that the formation of the phytolith and La(III) complex could be affected by exogenous La(III) and acid rain in germinated rice seeds.

Phytolith characteristics and preservation in trees from coniferous and broad-leaved mixed forest in an eastern mountainous area of Northeast China

Research on phytolith morphology and the preservation of phytoliths in soils provides the theoretical basis for reconstructing shifts in forest–grassland ecotones and the evolution of plant communities. Based initially on anatomical origin, then shape and finally texture, phytoliths in broad-leaved trees were divided into six major types, 10 types and 33 sub-types, respectively; and correspondingly phytoliths in coniferous trees were divided into seven major types, 9 types and 20 sub-types. Results of detrended correspondence analysis showed that broad-leaved trees were characterized by epidermal phytoliths, hair, hair base, sclereid, elongate attenuate, stomate and tracheids; while the main coniferous phytoliths were elongate, tabular, blocky and margin-cuneiform. In Pinaceae, Larix closely corresponded to elongate and margin-cuneiform; Picea and Abies to blocky scrobiculate, stomate and tracheids; while Pinus corresponded well with epidermal, blocky and tabular. Only five kinds of broad-leaved phytoliths and seven kinds of coniferous phytoliths appeared in soils. The preservation degree of different phytolith types was determined by comparing the contents of the same phytoliths in plants and soils. Evidence showed that coniferous phytoliths were better preserved than broad-leaved ones. Among coniferous phytoliths, the cubic, tabular echinate and elongate cavate phytoliths were better preserved than other types. Among broad-leaved phytoliths, sclereid and blocky facetate showed the best preservation. Overall, this research will support the more accurate use of tree phytoliths in interpreting paleo-environments and paleo-vegetation.

New evidence for rice cultivation from the Early Neolithic Hehuashan site

Phytolith analysis was conducted on soil samples from an archeological profile at the Hehuashan site, located in the upper Qiantang River region, China. This paper focuses on: (1) changes on the morphometric features of Oryza-type bulliform phytoliths from the rice leaves of the Early Neolithic Hehuashan site, (2) human adaptations during the Early Holocene, and (3) the cultivation of rice by Early Neolithic occupants in the upper Qiantang River region. The phytolith assemblage before and during the Early Neolithic Shangshan Culture occupation of the Hehuashan site indicates a landscape composed of reeds (Phragmites australis), rice (Oryza sp.), Bambusoideae, and some woody plants. The amount of Oryza-type bulliform phytoliths and the number of scale-like decorations present along their margins increased from the lowest to the uppermost deposits at the site. The change in the amount and morphology of bulliform phytoliths indicates the presence of wild rice around the site at the time of human occupation, which provides evidence of a shift from the collection and possible manipulation of wild rice to cultivation during the Shangshan Culture period (11400–8600 BP).

Machine learning algorithms improve the power of phytolith analysis: A case study of the tribe Oryzeae (Poaceae)

AbstractPhytoliths, as one of the important sources of microfossils, have been widely used in paleobotany‐related studies, especially in the grass family (Poaceae) where abundant phytoliths are found. Despite great efforts, several challenges remain when phytoliths are used in various studies, including the accurate description of phytolith morphology and the effective utilization of phytolith traits in taxon identification or discrimination. In this study, we analyzed over 1000 phytolith samples from 18 taxa representing seven main genera in the tribe Oryzeae (subfamily Ehrhartoideae) and five taxa in the subfamilies Bambusoideae and Pooideae. By focusing on Oryzeae, which has been extensively investigated in terms of taxonomy and phylogeny, we were able to evaluate the discrimination power of phytoliths at lower taxonomic levels in grasses. With the help of morphometric analysis and by introducing several machine learning algorithms, we found that 87.7% of the phytolith samples could be classified correctly at the genus level. In spite of slightly different performances, all four machine learning algorithms significantly increased the resolving power of phytolith evidence in taxon identification and discrimination compared with the traditional phytolith analysis. Therefore, we propose a pipeline of phytolith analyses based on machine learning algorithms, including data collection, morphometric analysis, model building, and taxon discrimination. The methodology and pipeline presented here should be applied to various studies across different groups of plants. This study provides new insights into the utilization of phytoliths in evolutionary and ecology studies involving grasses and plants in general.

Dating rice remains through phytolith carbon-14 study reveals domestication at the beginning of the Holocene

Phytolith remains of rice (Oryza sativa L.) recovered from the Shangshan site in the Lower Yangtze of China have previously been recognized as the earliest examples of rice cultivation. However, because of the poor preservation of macroplant fossils, many radiocarbon dates were derived from undifferentiated organic materials in pottery sherds. These materials remain a source of debate because of potential contamination by old carbon. Direct dating of the rice remains might serve to clarify their age. Here, we first validate the reliability of phytolith dating in the study region through a comparison with dates obtained from other material from the same layer or context. Our phytolith data indicate that rice remains retrieved from early stages of the Shangshan and Hehuashan sites have ages of approximately 9,400 and 9,000 calibrated years before the present, respectively. The morphology of rice bulliform phytoliths indicates they are closer to modern domesticated species than to wild species, suggesting that rice domestication may have begun at Shangshan during the beginning of the Holocene.

Chemistry of fruit wall and seed in Cyperaceae tribe Trilepideae

Transverse sections of the fruit walls and seeds from all four genera of family Cyperaceae tribe Trilepideae were investigated using SEM and energy dispersive x-ray analysis (EDXA) to determine the presence of different elements in different parts of the fruit wall and in phytin globules of the aleurone layer of the seed. This is a novel systematic method as previous investigations of elements in the fruit wall have focused almost exclusively on the morphology of silica phytoliths and not the actual occurrence of Si and other elements in the various parts of the fruit wall. In Cyperaceae seed presence of phytin globules rich in P, Mg and K in Cyperaceae seeds are here described and illustrated for the first time. Silicium-rich papillae were present in all epidermis cells of the pericarp in all genera in tribe Trilepideae, being an additional indication that the fruit-cover in this tribe is not an utricle but rather a pericarp. Although tribe Trilepideae is an early diverging clade within subfamily Cyperoideae, it has a pericarp typical of most of the subfamily, including the large genera Carex and Cyperus in the more derived clades.

Pericarp diversity in Cyperaceae tribe Scirpeae

Transverse sections of the pericarp or fruit wall of 28 species and 30 taxa from all genera of family Cyperaceae tribe Scirpeae sensu Goetghebeur (1998) were investigated using SEM and X-ray analysis to study cell types and presence of different elements. Two genera described after my analyses were completed (Calliscirpus and Rhodoscirpus) are excluded from this investigation; also the genus Cypringlea described in 2003. Particular attention was paid to variation in cell types and presence of silicon and other elements in the different parts of the pericarp. This is a novel systematic method as previous investigations of elements in the pericarp have focused on the morphology of silicon phytoliths and not the actual occurrence of Si and other elements in the various cells. Four of seven investigated and accepted genera have silicon phytoliths, but Si is present in all genera and in 25 of 28 investigated species or in 27 of 30 taxa. Other elements were present in minor amounts. However, the pericarp of Trichophorum uniflorum (Trautv.) Malyschev & Lukitsch. from arctic Russia had no silicon, but a conspicuous Ca-plate in the epidermis cells. Plant species with a pericarp with a thick silicon layer are better adapted to endozoochorous seed dispersal by protecting the seed from digestive acids and the abrasive action of grinding in birds’ gizzards; also the mineral layer and/or a thick outer epidermis wall will protect against an intense UV radiation regime, such as the high Andes and the arctic. The new information discovered through X-ray analysis of the pericarp has the possibility to increase the reliability in analyses of fossil fruits of Cyperaceae. Fruit wall anatomy provides good characters for generic delimitations in some instances, and provides significant infrageneric variation in other genera. Of the seven investigated genera only Trichophorum and Phylloscirpus were heterogeneous as regards fruit characters.

Phytolith analysis for the identification of barnyard millet (Echinochloa sp.) and its implications

Echinochloa was an important prehistoric food crop of early agriculture in Asia. Macro-remains can be used to identify Echinochloa. However, when few macro-remains are available, phytolith analysis can be performed. In this study, we examined the phytolith morphology of the glumes, lemmas, and paleas from the inflorescence bracts of nine Echinochloa species from different regions of China and obtained diagnostic, morphological, and morphometric characteristics for Echinochloa. Phytoliths in Echinochloa are different from those in most known crops except those in Setaria italica and Panicum miliaceum. We found the following two diagnostic features within an epidermal silica layer that can be used to distinguish Echinochloa sp. from S. italica and P. miliaceum: (1) the β-type undulated patterns with constricted top of the undulation amplitude and (2) the discriminant functions based on the morphometric data of the β-type undulated patterns, which suggested that 94.9 % of the cross-validated data were correctly classified into Echinochloa, S. italica, and P. miliaceum. Thus, we established the phytolith identification criteria for Echinochloa; this could have important implications in plant taxonomy, archaeobotany, and plant domestication.

Phytoliths as a method of identification for three genera of woody bamboos (Bambusoideae) in tropical southwest China

In order to explore the relation between phytolith morphology and plant taxonomy, we conducted a comparative research on the morphological features of phytoliths from 26 woody bamboo species within 3 genera of Bambusoideae in tropical southwest China. All morphological parameters were measured at 500× magnification using an Olympus BX51 light microscope. Three-dimensional scattered plots and hierarchical cluster analysis were performed using SPSS 13.0 software. The leaves of woody bamboos contain a great diversity of phytolith types including short cells, long cells, bulliform cells, hair cells, mesophyll and vascular tissues, of which cuneiform bulliform cells and oblong concave saddles were significant in clarifying the position of controversial Dendrocalamopsis group. Detailed research on phytolith morphology demonstrated that most of the overlap within this group occurs among long cells, bilobates, parallepipedal bulliform cells, hair cells, mesophyll and vascular tissues at the genus level. Oblong concave saddles exhibited taxonomical value both at the subfamily and genus levels. Comparative research on the morphological parameters of cuneiform bulliform cells and oblong concave saddles indicated Dendrocalamopsis has a separate partition from Bambusa and Dendrocalamus, which might provide strong evidence that Dendrocalamopsis should be an independent genus within Bambusoideae. Hierarchical cluster analysis on the cuneiform bulliform cells and oblong concave saddles indicated that Dendrocalamopsis is more closely related to Bambusa than Dendrocalamus. At the genus level, cuneiform bulliform cells and oblong concave saddles together exhibit taxonomical value.

Differentiation of globular phytoliths in Arecaceae and other monocotyledons: morphological description for paleobotanical application

Globular phytoliths have been mainly assigned to palms, woody trees, and other monocotyledon families from tropical regions. The lack of detailed descriptions of this phytolith morphology and its correct assignments to particular groups could lead to erroneous interpretations of phytolith records. In order to improve paleobotanical interpretations of phytoliths records, we analyzed the phytolith content and described the quantitative and qualitative characters of globular phytoliths of Arecaceae, Bromeliaceae, Cannaceae, Marantaceae, Orchidaceae, Strelitziaceae, and Zingiberaceae species from Argentina. Phytoliths were extracted by calcination and multivariate analyses were used to analyze their taxonomic relevance. Phytolith assemblages allowed the differentiation 1) among Zingiberales species; 2) among Arecaceae species; 3) between Orchidaceae, Arecaceae, and Bromeliaceae families; and 4) between Zingiberales and the rest of the groups. The study of distinguishing features of globular morphologies (such as size, roundness, reniformity, number of spines, spine length, and density of spines) allowed the discrimination between two Arecaceae subfamilies, and among Bromeliaceae, Cannaceae, and Zingiberaceae families. This work showed the importance of both analyses (phytolith assemblages and phytolith morphometric) in the identification of groups at different levels and represented the first detailed and comparative description of globular phytoliths of palms and other monocotyledons from Argentina.

Study of morphology and chemical composition of phytoliths on the surface of paddy straw

Silica though nutritionally insignificant plays important role in plants. Most of the silica from absorbed water is precipitated and deposited inside or between plant cells to form ‘phytoliths’ which provide mechanical strength and aid in protection from physical, chemical and biological stresses of the plant. Phytoliths occur in numerous monocot and dicot plants. These amorphous silica bodies take various shapes and sizes depending on their intracellular or intercellular templates, that certain morphological forms are even specific to families or species. In the present study, paddy straw samples were examined using scanning electron microscopy to visualise silica deposition (phytoliths) on the surface followed by Energy dispersive X-ray spectroscopic analysis to determine the composition of the observed phytoliths. A protective coat of silica covering the entire surface of paddy straw, consisting of phytoliths of distinct shapes and sizes and diffused silica deposits, was observed. Phytoliths observed were morphologically different, some forms being exclusive to certain regions of paddy straw. Indiscrete deposits of silica were found between and around phytoliths. Elements like Fe, Al, K, Mg, Cu and Ca were detected in addition to Si, O and C in phytoliths indicating that phytolith deposition occurs as a part of the inherent mineral detoxification system in paddy. The surface silica deposits, being the first to encounter physical and biological stress factors, play the major role in resistance of the plant.

Comparison of dry ashing and wet oxidation methods for recovering articulated husk phytoliths of foxtail millet and common millet from archaeological soil

Phytolith research on foxtail and common millets represent one of the keys to explore early agricultural activities in the Yellow River basin in China. However, the phytoliths of these two millets easily disintegrate during burial and the extraction process. In this paper, both dry ashing and wet oxidation methods were applied to determine the effects on phytolith extraction from archaeological soil samples. The results indicated that the dry ashing method had two significant advantages over wet oxidation: (1) the morphology of husk phytoliths was retained to a greater extent; and (2) nearly all the charcoalified tissues were removed successfully. The dry ashing method proved to be a better method for phytolith extraction of both foxtail millet as well as common millet from archaeological samples.

Understanding Holocene variations in the vegetation of Sao Joao River basin, southeastern coast of Brazil, using phytolith and carbon isotopic analyses

To understand variations in the vegetation of the southeastern coast of Brazil during the Holocene and to identify roughly when they took place, we make use of phytolith morphology and carbon stable isotope analyses coupled with 14C dating of soil profiles. The soil profile studied is located in the Sao Joao River Basin close to Cabo Frio, Rio de Janeiro State. We evaluated the soil characteristics, which showed great variations in granulometry, with larger texture in upper horizons that enabled the movement of particles to lower layers. The accumulation soil horizons revealed several palaeoclimatic aspects: higher phytolith stocks, a higher density of trees, and a lower water stress at the bottom of the profile, and a predominance of C3 grasses throughout the Holocene. Carbon stable isotopic ratios of the soil profile confirm the predominance of C3 plants, except for E/Bt horizon which was enriched in 13C. The soil organic matter mean residence time ranges from post-bomb (topsoil) to 10,245yearscal BP at the base of the profile. The results of this study are compatible with other evidence of a more humid environment in the first half of the Holocene.

Phytoliths in Pottery Reveal the Use of Spice in European Prehistoric Cuisine

Here we present evidence of phytoliths preserved in carbonised food deposits on prehistoric pottery from the western Baltic dating from 6,100 cal BP to 5750 cal BP. Based on comparisons to over 120 European and Asian species, our observations are consistent with phytolith morphologies observed in modern garlic mustard seed (Alliaria petiolata (M. Bieb) Cavara & Grande). As this seed has a strong flavour, little nutritional value, and the phytoliths are found in pots along with terrestrial and marine animal residues, these findings are the first direct evidence for the spicing of food in European prehistoric cuisine. Our evidence suggests a much greater antiquity to the spicing of foods than is evident from the macrofossil record, and challenges the view that plants were exploited by hunter-gatherers and early agriculturalists solely for energy requirements, rather than taste.