#27 Murder in the Bloom: Forensic Botany 101 II

Hello, and welcome back, folks, to another episode of STEM on the Streets! If you are new here, my name is Aiza, and this is my partner, CAI (crime AI). Together, we stroll through the criminal-ridden streets of STEM!

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How could a leaf tell a story?

Last time we asked if a leaf could tell a story, the answer wasn’t a hard no, but now we ask: how could a leaf tell a story?

This time we step into a lab- metaphorically, obviously, unless you have one nearby. We will take a closer look at the techniques that turn the sneeze-inducing pollen into expert testimony. What secrets lie in pollen? How do we discover these secrets? And why are these fragments of Mother Nature so reliable- and so hard to fake?

Let’s dig deeper. (Sorry. Plant pun. I couldn’t help it.)

The Whispers of Pollen: Palynology

Imagine walking through a meadow and carrying a secretary so teeny tiny that you’d need a microscope to see it. You know what that is? Those little things that make you sneeze? Sometimes, the yellow powder you get when you touch the center of a flower? That is pollen. Despite its microscopic size, in the world of forensics and crime, these tiny things make the largest differences. 

Pollen analysis, or- if we feel fancy- palynology, is one of the most common and frequently used methods in forensic botany.  All plants release unique microscopic grains- almost like a botanical fingerprint- typically between 7 and 200 µm in size (that is very tiny!). These unique grains are almost everywhere you can think of. Clothes? Yes. Hair? Yes. Shoes? Yes. Nostrils? Yes, there too. They are almost everywhere because they cling stubbornly to different surfaces. And because different plants have different blooming seasons and are found in different regions, their pollen can help identify the time and location of where or when someone or something has been. So yes, pollen is like a microscopic tracking device that you may have in your nostrils. 

Image of pollen under a microscope.

Forensic palynologists collect and analyse trapped pollen on people or objects and compare it to the known regional pollen profiles. Since pollen grains are extraordinarily durable due to their protective sporopollenin-rich outer shell, they can survive for weeks, months, years, decades, and even more, offering credible evidence long after the event or incident. 

But beyond the circles of forensics and crime, palynology plays a diverse role, reaching areas in archaeology, climate science, and environmental monitoring. For example, ancient pollen layers have helped reconstruct past ecosystems. And in the legal context, which we talk of,  pollen can identify where smuggled plant species came from or if someone had handled a protected plant species.

Palynology in Archaeology

  Hey CAI, wanna do this one?

 (✿◡‿◡) CAI: Sure

Pollen grains serve as valuable time capsules in archaeology. Pollen has these durable outer shells, which help preserve it within the sediments for hundreds and millions of years. This allows scientists to reconstruct and visualize human activity, climate shifts, and vegetation.

A nice example would be the pollen evidence from 66 million years ago that showed there was an asteroid that caused disruptions in the ecosystem, and also the following gradual ecological recovery. Another one is the sediment cores found in Western Australia, showing the transition from tropical forests to vegetation that was adapted to tolerate drought as the climate became drier. Pollen layers from Lake Izabal in Guatemala illustrated deforestation during the collapse of the Mayan civilization, which was followed by the regeneration of the forest.

Palynology in Illegal Plant Trade

  Pollen analysis helps with more than just archaeology and ecosystems, but also with the monitoring of plant populations and detecting illegal trafficking of plants. Wild plants are often illegally harvested and sold on e-commerce platforms and social media, and they are harvested at such rates that they are endangered. Palynology can help monitor these plants and prevent illegal harvesting.

Palynology in Environmental Sciences

  Beyond archaeology, pollen analysis plays an important role in environmental sciences by tracking changes in ecosystems and climate over time. Multiple studies have shown that increases in the concentration of carbon dioxide and atmospheric temperature raise the pollen concentration, which also raises the potential implications of allergic diseases. When the spring temperatures are warmer, some plants start to produce pollen earlier, while warmer autumn seasons can cause the extension of growing seasons for other plants, such as ragweed. These shifts in pollen behavior can reflect ongoing climate change, with the current pollen also becoming a future historical record.

Well, that is all for today's episode!

This is Aiza Jamil signing out!

I am a forensics sleuth. What's your mystery to solve?

Citings