By Wendy Langhans
Many years ago, I made the mistake of sleep-walking through my introductory botany class. But every now and then, my youthful indiscretion catches up with me. Like earlier this week, when a friend ended her e-mail with a bit of botanical “cheesecake” humor: “Check out those glandular trichomes!"I cringed sheeplishly, because I had no idea what “trichomes” were. So I googled the phrase and discovered it meant “epidural outgrowths”, taken from the Greek for “growth of hair”, or in other words, “plant hair”. And sure enough, the flower stem in the photo was covered with fuzzy plant hair.
Here's an example of fuzzy plant hair on this Fiddleneck
There are two basic kinds of plant hairs - those with little Tootsie-Roll-Pop-like globs (glandular trichomes ) and those without (non-gladular trichomes). Non-glandular trichomes can be useful to plants in all sorts of bio-mechanical ways:
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- Discourage herbivores by mechanical means. For example, who wants to bite into something prickly and sharp? And curved tricomes with sharp ends can trap and kill small insects.
- Guide and detain pollinators to the right spot for pollination - sort of like a turnstile for insects.
- Protect against frost damage, by providing a place for ice crystals to form away from the plant’s surface.
- Moderate temperature at the plant’s surface by reflecting solar radiation.
- Conserve water, by breaking up the flow of air across the surface of the plant, thereby reducing evaporation.
But the bio-chemical functions of glandular trichomes  is where things get interesting, sometimes painfully so. Trichome glands store chemicals at the surface of the plant, chemicals that are designed to interact with pests and pollinators. Secretions from glandular trichomes, such as chlorogenic acid in tomato leaves, can be poisonous to insects. And we also know that physical contact with certain plants causes an allergic contact dermatitis in large mamalian herbivores (like ourselves).
Contact with Stinging Nettle can cause an allergic reaction. Photo courtesy Steve Ioerger
But not all trichomes produce harmful chemicals. Others may produce fragrant chemicals that attract pollinating insects (as well as gardeners and amateur photographers).
Great Spangled Fritillary perched on a Coneflower in Monticello, VA
So the next time someone asks me to “Check out those glandular trichomes”, I’ll be ready. And I’m sure that somewhere, my old botany professor is smiling.
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