EEB Ph.D. student Rosemary Glos studies the tiny hairs on leaves, called trichomes, which play an outsized role in plant survival. Thanks to the U-M Herbarium, and its extensive collections, she can examine dozens of species from around the world—without leaving her microscope.

Working with Associate Professor Marjorie Weber, Rosy researches how trichomes serve multiple purposes: protecting leaves from harsh sunlight, insulating plants, defending against herbivores, and even helping carnivorous plants capture prey.

“I’ve been thinking about trichomes a little more like plant feathers,” Rosy says. Just as bird feathers vary—from giant peacock plumes to the soft down of chicks—trichomes also display extraordinary diversity. They can be barbed, sticky, long, or short, and each type serves different functions.

To study this diversity, Rosy uses Herbarium specimens to measure trichome density, size, and shape. She pairs this work with experiments on how these structures affect insects like caterpillars. Trichomes, which offer a physical defense, can interact with chemical defenses, creating a double layer of protection for the plant. Rosy says this is a bit like “chewing glass while drinking poison.”

Rosy’s research focuses on the Blazingstars (Mentzelia), also known as “stick leaves,” which have glassy, stiff hairs with recurved barbs. “They’re like plant Velcro,” she says. Examining these leaves under a microscope allows her to document trichome patterns and relate them to environmental factors such as latitude, temperature, and moisture.

Her work also explores the trade-off plants face: attracting pollinators while deterring herbivores. Plants with larger flowers that lure pollinators often have fewer sticky hairs, reducing the risk of trapping helpful insects while still defending against pests.

Another way that Rosy uses Herbarium specimens is by germinating seeds—some decades old!—to grow living plants for further study. “One plant I’m growing from a 1968 seed gives me the chance to compare fresh trichomes to preserved ones, which is incredible,” she says. This approach opens a window into rare or distant species that are hard to cultivate.

Rosy’s research highlights the hidden complexity of plants, and the “feathers” that protect them. Her work also demonstrates how the careful study of both preserved and living specimens can reveal how plants interact within their environment, and evolve over time.