Pollen: The Hidden World of Flowers

August 11, 2022

Everyone appreciates the world’s pollinators, such as bees, butterflies, and more, but when it comes down to giving pollen itself credit, we often fall short. This summer, high school students and recent graduates in the Midland area are taking part in the Michigan State University St. Andrews Research Internship. These students are gaining an interesting insight into the innerworkings of pollen and flowers within the diverse biosphere of Dow Gardens and how it relates to local pollinators, specifically bees. By harvesting pollen from flowers in Dow Gardens and comparing it to what bees in Whiting Forest are collecting, we can better understand the journey of our local pollinators.

The process of collecting pollen is, dare we say, an art. When walking through Dow Gardens, the plethora of flowers presented to us was astonishing. We started by collecting flower heads, tastefully, making sure to not cause an eyesore in the exhibit. From there, we took these flowers back to the St. Andrews lab, and that is where the magic began. Using toothpicks, tweezers, and gravity, we shook, plucked, and scraped pollen onto microscope slides, and observed at multiple magnifications. We observed many different shapes and structures of pollen. Using cameras attached to our microscopes, we photographed the pollen grains, allowing us to characterize the pollen beyond words and numbers. We also washed the pollen with alcohol, separating pollen grains by removing a layer of oil often found on the surface, and giving a more defined image. We broadened our investigation by using a medium called glycerol, which allowed us to focus on the border of the pollen grains and made them more translucent. This led to images comparable to online resources of pollen grains, which helped in identification. By the end of just our second week, we were often yielding photos equal to, or even better than, online resources. We were eager for what future flowers would hold for us!

Once we had all these images, we had to find traits which could tell them apart. We began by measuring the dimensions of the pollen grains in micrometers. There are 25,400 micrometers/µm in 1 inch! To do this, we had to calibrate our microscopes, converting pixels on the screen into micrometers. Over weeks of collection, our group has harvested pollen from over 200 distinct types of flowers from Dow Gardens. We placed all our data, including size, shape, texture, and structure, into a spreadsheet, excited to compare them to what types of pollen the honeybees have collected. (Stay tuned for future communications!)

After obtaining the best images with each method, we were presented with incredibly detailed and intricate structures. Many flowers yielded small circular pollen with spikes like a sea urchin. Other times, we were left with oval grains with network-like structures, or even smooth skins. Overall, pollen could have many types of shapes and surfaces, as well as creases, pores, and vastly different sizes. As you may expect, these features all have scientific terminology. For example, those spiky balls can be described as echinate spherical structures, while the long grains with networks are called perprolate and reticulate. Even smooth, rock-like surfaces have a name: psilate.

Husker red penstemon (*Penstemon digitalis)*

Another very interesting structure that we encountered was called fenestrate, alluding to the window-like gaps, surrounded by ridges, that can be seen in the pollen.

Perennial sow thistle (*Sonchus arvensis*)

One main way to tell pollen grains apart is by the creases, otherwise known as colpi, as seen in the field thistle pollen (above). The pollen we saw ranged from 0 to 6 colpi. Pollen can also have pores, and sometimes they reside in the folds (called colporate), adding to the uniqueness of each grain. One might assume that pollen grains are all one size, but we discovered a wide array of sizes. For instance, forget-me-nots had pollen grains measuring 6×3 µm, while bigfruit evening primrose had grains that were about 160 x 125 µm.

Forget-me-not pollen (tiny!)
(*Myosotis latifoli*)

You may have noticed that the forget-me-nots had 2 grains attached to each other; this formation is called a dyad, meaning that when the pollen from the flower matures, it falls off in pairs. Similarly, we found that cattail had a cluster of 4 grains which can be referred to as a tetrad.

All in all, we were able to get a better grasp of the individuality of each flower and its pollen. However, these observations did not come without hurdles. One of the direst problems our team faced was calibrating the measurements on each group’s microscope. Despite unfamiliar technology, we conquered the goliath feat of verifying that all our microscopes were correct to within a few percent. To ensure this, we used various calibration methods, paving the way for pollen analysis. While some of the flowers yielded hefty servings of pollen, others were as dry as the Sahara dessert. The worst of the pollenless perpetrators was the milkweed family which, despite our repeated gatherings, never failed to come up barren. In some instances, we resorted to looking at the anthers, the part of the flower where pollen is made, for any remnants that may have escaped pollinators.

This entire process opened our eyes to a new world beyond the beautiful petals of flowers. Even while studying pollen over multiple weeks, we never found ourselves bored in the process of data collection and research. We have learned more about pollen in one summer than most will learn in a lifetime. Pollen is vital to our planet, and all its inhabitants. Even if bees and butterflies take a great deal of the credit, pollen itself keeps our world turning. Thank you for reading our communication, and we hope you will take a minute to appreciate the millions of micrometer pollen grains surrounding you as you enjoy Dow Gardens!