When suspected marijuana hits the lab, how do they identify it? What are the steps of taking a bag of green leaves and determining for sure that it is marijuana? This is an issue that has long been a part of crime labs as they labor to produce evidence for convictions.
With the modern legalization of hemp, this issue becomes even more critical. The two plants are indistinguishable from sight and smell alone. We need to be aware of what tests we are currently doing to positively identify marijuana and what needs to be done to distinguish hemp from marijuana.
Today in forensic science, the Thorton-Nakumura protocol is widely used in the U.S. to identify the plant. This article focuses on the first test, microscopic morphological examination.
What is the test?
The test involves looking through a microscope to identify the plant. The botanical identification is made based on visual inspection of morphological features. Morphological here means the form of the plants, their different structures, and how those structures are related.
How is it done?
A small amount of the plant is selected as the sample. The examiner places the sample on a microscopic slide with a drop or two of water. The sample is then looked at from different magnifications and under different lighting.
The test is looking for two different features on the sample. They are looking for cystolithic and glandular hairs. Cytosolic hairs kind of resemble the thorns on a rose stem, or an animals claws. Glandular hairs are stalks with bulbs on the end and look much like mushrooms. Several drops of hydrochloric acid are then added to the sample to check for effervescence or little bubbles forming on the sample. Once the sample has been examined, it is discarded.
Who is performing the test?
A lab technician performs the test. How valid the test is depends on the expertise the technician has in botany and microscopy. Formal training is hard to find in the U.S. Most technicians receive on the job training from someone who is also not a trained botanist.
How accurate is the test?
This test has the potential to be verifiable and accurate. Digital cameras can be linked to the microscope to take photographic evidence of what the analyst saw. Labs could do this, but few if any make any kind of record for this type of analysis.
The sample can also be double-checked by a peer to verify the findings. This is rarely done too. One
person checks the sample, and then the sample moves on to the next test with no verifiable report to reference for scrutiny later.
There is also the question of how valid the qualifications are for the test. There are no definitive studies that state that having cystolithic and glandular hairs prove that the plant contains THC. A number of unrelated plants also have these same features. The test is purposefully simplified so that it can be carried out by less skilled technicians. There are many other features that cannabis has, such as sessile glands, serrated edges of the leaves and compound palmate structure, meaning several leaflets arise from the same point. This form of identification is only able to identify cannabis. It does nothing to address the differences between hemp and marijuana.
