Brief summary... Now let me tell you the basics you need to know about phytoliths and the “world of phytoliths”...
The name phytolith comes from the Greek words phyto (plant) and lithos (stones). Its meaning refers to the particles vegetal origin. Phytoliths are actually silica particles stemming from the epidermis of the plant. Other synonyms for phytoliths are opal phytolith, silica cells, grass opal, plant opal or biogenic opal.
|Phytoliths in planr epidermis - X-ray picture (Cheng, 1989)|
Phytoliths are optically isotropic materials that are produced in the tissues of living plants in the course of their vital functions. They are mostly hydrated silica (SiO2 x nH2O), but they can also contain other trace elements (Al, Fe, Cu, N, P, etc.) They can be recognised and identified microscopically. Their specific density is between 1,5 - 2,3 g/cm³ Their colour may vary from colourless or transparent through pink to yellow. They are typically 5-200 micron in size; most of them are between 10 and 30 micron (just to compare: the human hair’s diameter is 100 micron). Phytoliths can be found in living plants but usually when the plant dies phytoliths are released into the soil. Usually we can find 2-20 mg phytolith in 1g of dry sample though this may vary at different types of plants.
Why and how do phytoliths separate from plants’ tissues?
It’s important to know that plants’ ability to produce phytolith differs. The climate, the physical and chemical attributes of the soil, the age of the plant and its place in the taxonomy all play a role in the phytolith producing ability. There are plants that produce a great amount of phytolith (Family of Grasses-Poacaea) while others produce nothing like the cassava (Manihot esculenta) (Piperno, 1988). It’s essential for plants to absorb silicone dioxide in the form of orthosilica or monosilica to produce phytolith. They do this through their roots and at 2-9 pH. It’s not clear yet whether they absorb quartz in solution via active or passive transport. Researches have examples for both cases.
The phytolith separation can take place in three places in a plant (Piperno,1988):
|Phytoliths in plant epidermis|
The role and importance of phytoliths is varied in the life of a plant. Iler (1979) discovered the following relation: for some plants the more silicone dioxide they absorb the better is the plant’s defence against fungi causing mycosis. Simpson and Volcani (1981) said that the silicone dioxide found in plants is not only essential in hardening the cell wall but also in the metabolism of the plant.
What do we use phytoliths for? Why are researchers interested in them?
Scientist got interested in these little particles in early days but they had to wait until suitable technology was available to study them. As soon as microscopes appeared researches started. The first researcher studying phytoliths was A.G. Struve who examined phytoliths in recent plants in Germany in 1835. This is said to be the starting point of phytolith researches. Until the Second World War the main researches took place in Europe with scientists like Ehrenberg, Grob, Haberlandt, and Mobius. After WW2 Americans, Japanese and Russian researchers also achieved great results. By that time some basic identification line diagrams appeared. From the middle of the 20th century phytoliths were examined from ecological aspect. Gaining much information became the basis of archaeological researches starting in the 1970s. By this time archaeologists also tried to meet the higher requirements of giving a more exact picture of the living conditions of earlier times. For changes of the environment could affect the lives of civilizations, it could cause their rise or fall. The new ecological views also expected that the researchers would explore in details the relation of humans and their environment. The history of phytolith research in Hungary can be summed up easily. Students can learn about them during Biology courses studying plant anatomy or plant physiology.
Meeting the high level requirements of paleoenvironmental reconstruction is only possible in teamwork and with thorough researches and information. Several factors are responsible for the state of given conditions which makes the reconstruction difficult. It’s hard to tell how a given area looked like 500, 5.000 or even 50.000 years ago. The terrain, the climate, the flora or the fauna may have changed. To discover the changes we need to gain as much information as possible about environmental factors. Since most of the direct information got lost, the information that researchers actually have and can analyse become more valuablel.
|Methods of environmental reconstruction|
|Phytoliths in geological profile|
|Geological core for phytolith analysis|
For example if we examine a snail shell we can tell if in that particular area where it was found there had been water or not on the surface, and how deep it was. Was it a river or a lake? If we examine a carbonized seed we can tell what people who lived there had been growing. Examining pollen we can find out if there had been forests and also the types of trees in that area. Dendrochronology analyses the tree rings of the trees. Dendrochronologists can tell the changes of cold and warm seasons or wet and dry seasons by examining the thickness of the tree rings. These are just a few examples. If we have more data we can gain much more information.
Phytoliths can be used for such paleoenvironmental reconstructions very well. Obviously the more factors we examine the more accurate picture we can get. After a plant separates phytolith it produces an identity which is much more resistant than the plant itself. Even after the plant dies (rotting, burning), it indicates the type of plant that lived there. It’s easy to identify the plant by the size or shape of the phytolith. Often we can tell the species but even if not, it also helps to know whether grass or trees lived in that particular area. Examining the different attributes of phytoliths (morphology, size, colour etc) we can build models about the vegetation and we can even discover if a cultivated plant was improved by breeding. The morphology of the phytolith in cultivated plants undergoes changes. This was really useful when scientists were studying the corn producing lands of Indians of America (Latin America). Like every other identifying, it is important to create a reference material that is done by collecting plants, obtaining phytolith and taking photos of them.
To obtain phytolith it is best to use geological unperturbed core. It is also possible to get a comprehensive period sample from geological profile. By doing this we can follow a vegetation through a long period of time. When analysing from archaeological aspect it is best to get a sample from one object or one stratum. It is possible to analyse a dung-pit where the waste was thrown or a millstone which also can contain phytolith on its surface. We can do the research on phytolith stuck on human or animal teeth or the remains of a fireplace.
The phytolith research has strengths and weaknesses as any other research:
Phytolith research nowadays
Phytoliths are not yet acknowledged everywhere but it is great to see that more and more researchers and scientist know and use the results of phytolith researches in paleoenvironmental reconstructions and also in archaeology. The Society of Phytolith Research gathers the researchers internationally and organises conferences. The first nomenclature was released (ICPN, 2005). The greatest scientist is Dolores R. Piperno who has written the most important books and countless articles about phytolith research, but Marco Madella, Terry Ball, Deborah M. Pearsall or Steve Weiner are also great names in this research field. I could go on with listing names but let me mention just two more to whom I m saying thank you for all their help and support: Mikhail Blinnikov (Minnesota) and Debora M. Zurro (Barcelona).