Northwestern University, Evanston, Illinois), and I have been steadily pursuing the study of plant exudates (e.g. resins, gums, kinos) and ambers (fossilized plant resins) worldwide for several decades. Through their chemistry as well as biological inclusions, in the case of amber, these materials help us understand our past. For example, amber materials we have studied from Chiapas, Mexico, contain inclusions, such as the base of a barnacle and carbonates strongly suggesting a tropical coastal environment million of years ago.
If the exudate happens to be a resin, the nuclear magnetic resonance NMR spectroscopy profile can help us determine the botanical provenance, such as the plant family and sometimes the genus. For instance, using the carbon-13 isotope, the resinous exudates of conifers can be placed into their correct family (e.g. Pinaceae, Cupressaceae, etc.). Additionally, the same resinous exudates of pines and their allies can be further correctly identified to genera if proton NMR is performed.
Some key discoveries resulting from those efforts have included the establishment of a typology of ambers of the world as well as a classification of modern plant exudates of the world. Although exudates have distinct physical properties, looks can be deceiving. An exudate collected from Pinus coulteri D. Don (Pinaceae) is a resin and it is the most commonly collected exudate in conifers. Milky exudates, often called latexes, are also resins, as in the materials oozed by Euphorbia tirrucali L. (Euphorbiaceae). Exudates from cherry trees, like those that ornate our nation’s capital, are gums, as in the case of Prunus sp. (Rosaceae).
Exudates are ubiquitous in the plant world. If any reader sees materials that look like plant exudates, I will appreciate a sample (100 mg or the approximate volume of an eraser on a pencil) or knowing about who to contact to collect such materials.