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.
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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
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.
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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:
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.
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
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 combined.
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:
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.
Stem more or less hairy, sometimes not.
Stem hairless or nearly so.
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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."
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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 establishment.
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.
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The Names of Plants - Guide to Plant Collection & Identification © Jane M. Bowles 1996