Many
important taxonomic characters are difficult or impossible to observe with the
naked eye. For example, you may wish to count the number of tiny teeth at the
apex of a ray floret of a composite, or determine whether a leaf has minute
hairs in the axils of the veins. Anatomical structure of parts such as roots
and bark is particularly hard to see. A good hand lens, used in good light,
will suffice for many purposes. However, for those who will be looking at a
great deal of material, a dissecting microscope is very useful. This should not
be confused with a light microscope, which has a built-in light in the base, a
raised stage for slides, and several objective lenses for increased
magnification. A dissecting microscope has a much lower range of magnification
and a low stage on which a fairly large object can be placed, with room under
the head of the microscope for hands holding tweezers, etc. A separate lamp
illuminates the object. Dissecting microscopes are much more comfortable to use
than hand lenses, with binocular eyepieces and a greater maximum magnification
that provides better resolution of very small features. Forceps and perhaps
dissecting needles should also be obtained, as they allow convenient
manipulation of small plant parts.
One
must expect harvested plant material, even of a whole herb, to look very
different from live plants of the same species. Unless plants are small, people
do not normally collect whole plants. Larger plants would typically be cut or
broken into pieces; only the tops may be collected, or lower leaves may be
stripped from thick stems, which are then discarded. Since dried material is
often brittle, more breakage can occur during initial processing. Some
characters, such as the height of a large plant, usually cannot be observed,
and others may be observed only imperfectly. For example, if a plant has large,
petiolate lower leaves but smaller, sessile upper leaves, broken pieces with
each type of leaf base may be found, but not attached to a stem in a neat
sequence.
Dried
material also may change appearance greatly by shriveling, which can make parts
hard to measure, and colors may change to some extent (although if colors are
too faded, it is often an indication of poor quality due to improper
processing). Dried flowers may lose parts such as petals, which may be found
loose. Most dried leaves, flowers, and fleshy fruits are more easily examined
if they are rehydrated. Various wetting solutions may be used to rehydrate
herbarium material. The simplest is to use hot water with a very tiny spot of
dish soap in a watch glass or similar container. Solid or hard fruits do not
rehydrate as quickly, and the use of boiling water can be helpful. With a few
chemicals, a more efficient wetting solution can be made. Dr. Lynn Clark’s
Modified Pohl’s Solution (based on a recipe by the late Dr. Richard Pohl) uses
750 ml distilled water, 250 ml 1-propanol, and 2 ml Ivory liquid soap to make
one liter of solution; it can be kept in dropper bottles. Once material has
softened, it can be spread out with forceps so that its original shape and size
can be seen.
Sometimes
the initial processing of an herb leaves it broken into rather small pieces,
which is less than ideal, but informative parts may be found with patience and
care. Small flowers often remain intact in broken material, although
inflorescences usually do not. Information regarding the likely shapes of the
leaf base, apex, or margins, the venation pattern and the presence of surface
pubescence or glands may be obtained from broken leaves by sorting through the
pieces to find those that include suitable portions of the leaf. If leaves are
broken, it may or may not be possible to estimate their size accurately by
examining the larger pieces. Leaf size is more likely to be an important
character in plants that have uniformly small leaves, rather than those that
have leaves potentially ranging in size from small to enormous. Small leaves,
even when broken, often include enough of the leaf in a single piece to allow
some estimate of the size to be made. (The exception is if material has been
comminuted, or broken into tiny fragments in which few taxonomic characters
remain visible. A few plants are traditionally treated like this during their
initial processing, but botanicals of Western origin ought to have their
identity certified before they are processed to that degree.) Sliced roots and
rhizomes should be sorted through to find pieces that give the best view of the
internal structure, which means those that are cut most nearly straight across
rather than at an angle.
Fortunately,
quality control of botanicals does not usually involve actual identification,
but confirmation of identity. One doesn’t start with an unlabeled unknown and
have to determine from scratch which of the 300,000 or so species of higher
plants it is, which can be an exhausting task even with the best of material. Rather,
one starts with a plant that has already been named by someone else, and must
determine only whether that initial identification seems to be correct. If not,
one simply rejects the material, without any need to figure out what it
actually is. Knowing what the plant is supposed to be makes the use of
botanical literature (including this manual) much simpler. One only has to look
up descriptions of the plant named and ask: are these consistent with the
material at hand, or not? The material can also be compared to illustrations,
or to previously obtained reference plant materials of known identity. Such
comparisons are not always straightforward: some plant species have highly
variable leaf shape or pubescence, for example, and material that does not look
much like a given illustration or reference sample might in fact be the same
species. Written descriptions can make it clear when features of a species are
variable, thus avoiding “false negatives” in which correctly identified
material is wrongly rejected.
For
those who are buying a large amount of a single botanical, a sampling scheme is
necessary to ensure that a sufficient amount of the material has been checked
for identity. Otherwise, one might by happenstance check the only portion of
the material that did not contain excessive levels of some adulterant! A useful
approach is outlined by the World Health Organization’s manual, Quality Control Methods for Medicinal Plant
Materials (1998). In WHO’s recommended system, at least 10% of the
containers in a batch should be sampled, rounded up, with a minimum of five
containers (or all of the containers if the batch includes four or fewer). For
each container, equal samples should be taken from the upper, middle and lower
portions of the material, mixed, then repeatedly mixed, quartered, and divided
in half by returning diagonally opposite portions to the container, until a
suitable amount remains. These samples would also be used for any laboratory
tests performed, such as ash content and screening for chemical markers, and
for preservation of voucher specimens for each batch in case doubts about its
identity should arise later.
Comparing
a written description to illustrations or to reference specimens often enhances
one’s mental picture of a plant. Previously obtained reference material of
known identity is particularly useful because it can convey information on
color, texture, and the like in more detail than any description or
illustration. To avoid “false negative” results in which the identity of
material is wrongly called into question, one must remember that an
illustration or a piece of reference material represents a single individual,
and thus can display only a portion of the variation that is present within a
species. For example, if the flower portrayed is hairless and the flowers of
the material to be identified are hairy, they may belong to the same species,
yet appear substantially different at first glance. In case of apparent
discrepancy between the material examined and the illustration or reference
material, one must therefore consult a written description to determine whether
the suspect character is indeed found in that species.
