3. PLANT IDENTIFICATION
3.1 The specimen
Before identification of a plant can begin it is necessary to have the best possible
specimen. Nearly all classifications and keys are based on the sexual parts of the plant
(the flowers and the fruit). One of the main reasons for this is that floral parts tend to
remain much more stable through time and under different environmental conditions than do
the vegetative parts, and they reflect the true relationships of plants better. However,
all parts, including underground organs may be needed for positive identification. A
flower and a leaf would not be enough if the key called for stem and root characters.
Notes about the plant should provide details of habit, growth form and so on (see Chapter 2). Bryophyte and lichen specimens should include
capsules and fruiting bodies where possible.
It is best to use fresh material for identification. When this is out of the question and preserved specimens have to be identified, the importance of good pressing and mounting techniques will be made very clear.
|[Back to TOP]|
3.2 Equipment needed
The most obvious need is a good reference book or books. The best books have at least
elementary keys. Line drawings or detailed paintings are more useful than most
professional taxonomists would care to admit. Colour photographs, although attractive, and
showing the plant in its natural habitat, are often next to useless because they cannot
show the range of detail which can be incorporated into a drawing. A list of a few
available floras and short reviews are given in Appendix II.
Another essential piece of equipment is a hand lens, dissecting microscope, or some
kind of magnifier. Even on large plants with big flowers, some of the features are very
small and positive decisions can only be made if all the features are clearly visible.
Other equipment, although not vital, will make life easier. Included in this category
are very fine forceps, two mounted needles and a sharp scalpel or razor blade. In
addition, lichens may be impossible to identify without three chemicals and droppers for
spot testing. These chemicals are concentrated potassium hydroxide, calcium hyperchlorite
(bleach) and phenylenediamine. Clear instructions for making up these chemicals are given
in Hale (1980). As most bryological keys are based on cell characteristics, determinations
are limited unless a compound microscope, glass slides, cover slips and a stain such as
methylene blue are available. Obviously this equipment cannot be carried in the field, and
many bryophytes, once they are known, can be recognized under a hand lens.
One very useful piece of equipment which is, unfortunately, not always available, is an experienced botanist who knows the flora and can confirm identifications. Botanists usually have a stock of salient features by which they can recognize plants even without flowers or fruit. These characters are not always clearly stated in reference books. It follows that a note book and pencil will always prove useful.
|[Back to TOP]|
Apart from flipping through a picture book or asking a expert, keys are the most direct way of identifying plants. A botanical key is a series of specially arranged statements. Working through a key separates plants with and without keys characters and gradually narrows down the number of possibilities. Eventually, if all goes well, the number of possibilities is reduced to one and the specimen is identified. A very simple example, based on Gleason (1978) illustrates the principle of a key. It relies on the fact that Indian pipe (Monotropa uniflora L.) is the only North American species without chlorophyll and with a singular, regular flower:
Plant without green colour
Flowers regular, radially symmetric
Flowers solitary, one to a stem................Indian pipe
Flowers several on each stem................Some other species
Flowers irregular................................................Some other species
Plant with green colour................................................All other species
This is an indented key and probably the most common type used in floras. Each pair of
mutually exclusive sentences is printed in the same column, beginning with the same word.
When the pair is far apart on the same page or on different pages a letter is used in
front of each statement so that both members of a pair are easily recognized. Indentation
continues with each successive sentence until the end point is reached.
Another type of key uses the same principle, of pairs of statements, but they are
arranged differently. Statements are numbered and lettered (83a, 83b), and are printed
together. At the end of each statement is another number which indicates the next pair of
statements to be considered. This type is of key is used particularly when long
descriptions or pictures are included in the key. Sometimes both sorts of keys are
Keys in which only one character at a time is considered are called monothetic. They
are of limited use because sometimes the character in question is not visible. Most keys
are polythetic where possible and contain statements which consider a number of
Keys can be extremely frustrating to use at first. They may call for features which
your specimen does not have, or demand a decision on pairs of statements like:
Stem more or less hairy, sometimes not.
Stem hairless or nearly so.
Sometimes an educated guess has to be made and steps retraced if the first choice leads nowhere. To find that a species description bears no resemblance to a carefully keyed out specimen can be very discouraging. Nevertheless, keys are the quickest and most accurate means of identifying unknown plants. Use of keys becomes easier with practice and familiarity. Careful examination of the specimen and full consideration of both statements always makes key use easier. Finding that a particularly difficult specimen actually matches its description is a reward in itself.
|[Back to TOP]|
3.4 Technical terms
One of the main reasons why keys and plant identification guides appear so difficult to
use is because of the large number of technical terms involved. This is unavoidable. Any
subject in any field is filled with technical terms, and in order to master the subject,
the terms must be understood. The following passage from Mark Twain "A Tramp
Abroad" , taken from Crum (1976) superbly illustrates the need for special terms in
order to describe harnessing a horse:
"The man stands up the horses on each side of the thing that projects from the front end of the wagon, throws the gear on top of the horses, and passes the thing that goes forward through a ring, and hauls it aft, and passes the other thing through the other ring and hauls it aft on the other side of the horse, opposite to the first one, after crossing them and bringing the loose end back and then buckles the other thing underneath the horse, and takes another thing and wraps it around the thing I spoke of before, and puts the other thing over each horse's head, and puts the iron thing in its mouth, and brings the ends of these things aft over his back, after buckling another one round under his neck, and hitching another thing on the thing that goes over his shoulders, and then takes the slack out of the thing I mentioned a while ago and fetches it aft and makes it fast to the thing that pulls the wagon, and hands the other thing up to the driver."
|[Back to TOP]|
3.5 Unidentifiable plants
Some plants do not seem to be identifiable even if they are carefully keyed out and all
the essential parts are present. These plants should be sent to an expert for
determination. If a likely candidate is not known locally, the specimen will have to be
sent away. It may be sent directly to a local herbarium, but usually it pays to find out
who is the best person to identify the particular plant or plants you have, and whether
they would be willing to do your determinations. Sometimes this service has to be paid
for, but usually it is done free if the specimen is donated to the person or
Other specimens are unidentifiable because they are incomplete. Usually the best method is to compare the unknown with specimens of known plants to see if the characters match. A local expert may recognize the specimen, but usually botanists and herbarium staff are unwilling to tackle incomplete specimens. In the last resort the species may have to remain unknown and appear as "Carex sp." or "Moss 83" in reports.
|[Back to TOP]|
|TABLE OF CONTENTS |THE NAMES OF PLANTS |PLANT COLLECTING
|PLANT IDENTIFICATION |REFERENCES|
|APPENDIX - THE MEANING OF SPECIFIC EPITHETS |APPENDIX - BIBLIOGRAPHY|
The Names of Plants - Guide to Plant Collection & Identification © Jane M. Bowles 1996