The Matrix Routine
“The routine” developed by Dr. Humberto Jimenez-Saa provides a systematic way of examining a plant specimen in order to determine its identity to the family, genus, or even species level. Follow the routine in conjunction with the Jimenz Matrix or a botanical key to identify your specimen. All you need for starting material is a branch and some leaves.
Is your specimen a monocot or dicot? Monocots have parallel leaf veination and usually have strap-like leaves. Some, like palms and aroids, have large leaves with pinnate veination, but the secondary veins are parallel. Dicots have veins that fan out in various netted patterns and are usually broad-leaved.
How are the leaves arranged along the stem (phyllotaxy)? Are they alternate? Opposite? Or are there 3 or more leaves at a node arranged in a whorl? Alternate leaves may be distichous, coming off the stem in two ranks in a well-defined left-right-left-right pattern. In other cases alternate leaves may be spirally arranged. Opposite-leaved plants are often decussate, meaning that one pair of opposite leaves is offset by 90° from the next pair of leaves.
Are leaves simple or compound?
- If compound are they pinnate (feathery with multiple leaflets coming off of an elongated continuation of the petiole known as a rachis) or palmate (hand-like with leaflets radiating from a single point)? (note that the “stem” of a leaflet is called the petiolule)
- If pinnate, are they mono- or bi-pinnate? (in bipinnate leaves, the leaflets themselves are pinnate)
- If mono-pinnate, do they have an even number of leaflets occurring in pairs along the rachis (paripinnate)? Or do they have an odd number of leaflets with a terminal leaflet at the end of the rachis (imparipinnate)?
- If palmately compound, how many leaflets do they have?
Are the margins of the leaves or leaflets entire (smooth) or serrate (toothed)? (Note that serrate leaves are not particularly common in the tropics.)
Are stipules present or absent? For some reason, much of tropical botany seems to hinge on these seemingly insignificant flaps of tissue, or the scars that they leave behind. Use a hand lens! Some are terminal, meaning they are located at the tip of a branch. Most are located where the petiole meets the stem. They are usually tiny and usually fall off by the time the leaf has matured. The only evidence of their presence may be a tiny scar.
Do cut stems or severed petioles yield exudations? Are the exudations clear and watery? Milky white? Yellow, orange, or red? Do exudations flow freely or do they need to be squeezed from the petiole?
Do crushed petioles exude slightly sticky mucilage? Chew up a petiole and then feel between thumb and forefinger while looking for sticky strands as you spread your fingers apart. (Don’t make the mistake of chewing on a leaf that clearly has milky white or colored latex, as it’s likely to be highly toxic! There is a real, but subtle, difference between mucilage and latex exudations.)
Is there an odor? Crush up the leaves and smell them. Or tear off a leaf and immediately smell the broken petiole. What kind of odor do you detect? Primitive “ranalean odor”, anise, turpentine, unripe avocado, guava, eucalyptus, rank, sweet, green bean, or just plain nasty? Or like crushed leaves?
Examine the upper and lower surfaces of the leaf carefully with a hand lens (an essential piece of field equipment). Experiment by holding the leaf up to the light. Are translucent dots, also called pellucid dots, visible? Are the pellucid spots only in the shape of round dots or are some shaped like dashes? Are pellucid dots larger at the margin of the leaf or uniform in size? Leaves with pellucid dots often have an odor as well.
Can you peel the bark? Does it peel in long strings, sometimes referred to as “strong bark” or “stringy bark”?
Are hairs present? Use a hand lens to determine if they are present and if they are star shaped (stellate) or T-shaped (as in Malpighiaceae) or some other shape? Are they white or brown?
How are the primary, secondary, and tertiary veins arranged?
If you can answer most of the questions, then you should be able to determine the family of your plant specimen using the Jimenez Matrix, Susan Letcher’s key, or Alwin Gentry’s key.
THE JIMENEZ MATRIX
The Matrix was developed by Dr. Humberto Jimenez Saa as a way of teaching dendrology, the science of tree identification, to students of all levels. It builds upon early work by Dr. Leslie Holdridge, a pioneer in tropical forestry and tropical ecology, aimed at elucidating plant families using only vegetative material. In tropical forests, leaves and bark are almost always available, but flowers and fruits are seasonal and often hidden from those of us who cannot access the canopy the same way as a monkey, bird, or bee. Traditional plant identification and classification is based on flowers which are readily available to most temperate zone botanists, but not easily accessible in most tropical forests.
Strictly speaking, The Matrix is not a taxonomic key. It does not set out to identify any and all plant specimens. It doesn’t even claim to work all the time. BUT it works MOST of the time and is relatively easy to use once you learn some basic terminology and agree to follow The Routine.
To truly appreciate the beauty of The Matrix and to master it, you should take one of the Tropical Dendrology courses offered by Dr. Humberto Jimenez-Saa.
Dr. Humberto Jimenez-Saa is an inspirational teacher. His deep connection to and passionate love of trees is infectious. It is hard to imagine anyone with a greater knowledge of tree identification. As a teacher, he is firmly committed to sharing this knowledge with his students or anyone with an interest in trees. After studying with Humberto, you will have a newfound appreciation for every tree, leaf, or stipule that you encounter anywhere in the world. His love of trees and zeal for teaching is matched by a love of life and hope for the future of humanity. He measures his remaining time on Earth by the need to identify and label as many plants as possible, and freely admits that he has at least another 50-60 years left before his work will be complete. Until then, he will continue to tell us “here’s another tree for you to study…”
Using the matrix…
The Matrix consists of eight sections and can fit on a mere 6 pages. Each section is based upon phyllotaxy (alternate, opposite, or whorled), leaf type (simple or compound), and the presence or absence of stipules. Once these three basic pieces of information have been determined, it is a matter of identifying the combination of two or three other traits that allow you to determine the family to which a plant belongs.
Please note that The Matrix is not complete. Each user may develop his own version of the matrix utilizing features that are easily remembered or observed by the user. As your botanical knowledge increases, you will certainly want to expand the matrix to accommodate your expanding list of plant families and genera. The Matrix presented here was constructed by Scott Shumway with the help of Dr. Jimenez-Saa as part of a course in Tropical Dendrology. The Matrix may be reproduced, but Dr. Humberto Jimenez-Saa should be properly credited as its creator.