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Extraction of macrofossils from peats and lake sediments / Identifying seeds and fruits

By: K.Gajewski

1) Extracting seeds and fruits from Quaternary sediments

Extracting seeds and fruits from wetland sediments is a relatively easy matter. It is, however, very time-consuming.

  1. Take a known volume of your sediment. If you have a core, you can simply cut it into lengths (after splitting); 5 cm of a 5 cm core, for example. Because of the diversity of wetland sediments, the actual volume you use can vary but the above is a good start. Make sure to save enough sediment on the core for radiocarbon dating or other analyses.
  2. The sediment can be soaked in warm KOH for several minutes, if needed. This step is not always necessary, but would be if the sediment has dried, for example.
  3. Wet-sieve the sediments through 4.0, 1.0 and 0.5 mm sieves. Use the small brass sieves, which are kept only for this purpose . Use a jet of water, but not too fast to break the seeds. Note that the 4 mm may not be necessary for some sediments. The material remaining on the sieve can be stored in small beakers (in the refrigerator) until used.
  4. A small volume of the material is placed on a petri dish under the dissecting microscope in a little bit of water. Using forceps, push the material from one side to the other, while extracting the seeds and fruits. These can be carefully lifted from the solution and put in small boxes which contain glycerin. They should probably be stored in the refrigerator to avoid fungal growth. Use one box per sample, and you can already sort them while placing them in the box. The boxes should contain enough glycerin to coat the seeds, but not too much so they float around.

2) Identifying seeds and fruits

There is no generally available key to the identification of seeds and fruits. You can find several texts to specific groups or to a specific region in the library page. Most texts on the identification of aquatic plants also illustrate the seeds. You can use these texts to see the general form of the seeds and fruits of specific groups. For example, seeds of Potamogeton are quite distinctive, as are the genera of Cyperaceae. There are tables summarizing the size and shape characteristics of some groups, such as Eleocharis, which are obtained from floras. However, you may need to do this for your taxa and for your region. After that, it is simply necessary to compare your seeds to the reference material.

Other plant parts can also tell you about past environments, but will not be dealt with here. See Lévesque et al on the library page for an introduction.



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