Collecting Seeds to make a Seed Herbarium
What is a Seed Herbarium?
A seed herbarium is a standardized and authenticated collection of seeds used for comparison and identification purposes. It is critical to the seed analysis process that incidental seeds found within the analyzed sample be identified properly and placed as either a weed or another crop.
Weeds further need to be determined as to whether they are noxious or common. Unknown seeds can be identified by "keying" them out using scientific identification keys, (a laborious process).
The seed herbarium comes into play as a visual comparison in this identification process. It may also be the primary, visual method of seed identification. It is critical to the value of the seed herbarium that each specimen is accurately identified with a "standardized sample".
The seed herbarium is organized by family according to a phylogenic (evolutionary grouping from simple to complex) classification system to show their relationship to each other. This facilitates the ease of finding each specimen and aids in the identification process.
Currently, the Cronquist Nomenclature System is the popular classification system in use for organizing seed herbariums. Alternately, you can arrange the herbarium alphabetically by family, genera, and species.
Collecting the Seeds
Collecting the seeds specimens is a critical event in the establishment of the seed herbarium. It is during this phase that positive identification occurs. Knowledge of botany and botanical terms is essential to the collection process.
Seeds are best collected from a positively identified plant. It is easier, and more accurate, to obtain a positive identification of the plant than from the seed itself.
The plant is "keyed out" using various botanical keys and identification texts. Comprehensive identification notes are usually taken and recorded on field data forms. Since most plants are identified through their flowers, often the seed collector needs to identify the plant early in the growing season and tag the identified plant so the seeds can be collected later in the growing season.
When the seeds have reached full maturity and dried down, you return to collect the seeds. Plant identification and collecting seeds off of a positively identified plant is the most reliable means of gaining authenticated herbarium specimens and the most critical element of the process.
When actually collecting the seed specimens, make positively sure that they are mature. The biggest mistake that many novice seed collectors make is to collect immature, "green" seed. It is important that you ascertain the maturity of the seed before collecting it.
Full maturity can be established by the color of pods and their dryness, fleshy seedcoats becoming hard, and cutting the seed open to make sure that it's filled fully.
With grasses it is important that the lemma and palea of the seed unit contain a caryopsis. The lemma and palea may have changed color from green to straw-colored but this does not mean that it contains the caryopsis.
Often dried florets contain only the male stamens. No seed and fruit development has occurred with these florets because of the poor pollination conditions during the flowering period. Immature seed will distort and change color when thoroughly dried and are then devoid of the characteristics making them useful in identification and comparison with other species.
Five to twenty-five seeds are all you need for your herbarium specimen. Try to get a range of size, maturity, color, and shape (if they vary in shape).
If the fruits are distinctive, collect them too. Often the analyst finds pod and fruit remnants in the inert portion of the analysis. These give insights to the identity of the species.
Once the samples are collected they should be brought home and dried thoroughly. Seeds should be placed in paper envelopes or bags to dry thoroughly. Small cloth bags work too. I don't suggest that you put them in plastic bags right away as they will mold if they have not reached complete dryness.
Labels as to the identity of the species should be placed with the seed or copies of the field notes used in identification of the plant/seed.
In a dry climate, you can leave them in a dry area for one to two weeks and a complete drying should occur within that time. In a moist climate you may need to dry them over silica gel. Don't dry them in an oven as the heat may change the color or other attributes. Natural drying is the best.
One last statement on collecting specimens: Species vary in appearance (especially color) from year to year and locality to locality. A good herbarium may contain more than one sample from each specimen as each may vary slightly from one another depending on its origin.
Now it's time to assemble your collection of seeds into a true Seed Herbarium.