Reading the Leaves

The veins in a leaf do more than store water for the plant; even plant leaves preserved as fossils. They can reveal what environmental conditions were like when and where the plant was growing.

Leaf veins are a passion for Zack Quirk, a National Science Foundation fellow and University of Michigan paleobotany PhD candidate, who’s been using the Academy’s Botany Collection to measure the length of veins in plants. He chose the Academy herbarium because of it wide range of specimens collected from around the world. To collect these plants on his own would be prohibitively expensive and time-consuming.

The Academy’s herbarium has a large collection of specimens in the family Pandanaceae like the one above, collected in 1965 by former curator Benjamin Stone in the Caroline Islands in the western Pacific Ocean.

Leaf Veins 101

Plant leaves are sometimes preserved as fossils well enough that scientists can measure their veins, according to Jordan Teisher, the Academy’s Botany Collection manager. Teisher has been sampling the specimens and sending them to Quirk because COVID-19 has prevented in-person visits to the collection.

“Vein length per area is a measure of the average vein density in the leaf,” explained Teisher. “Since these veins are how plants conduct water, the average vein density of a leaf is correlated with how easily water can move through that leaf, and that is often correlated with the environmental conditions under which the plant is growing.”

For example, some plants growing in very dry conditions have a high vein length per area to prevent damage to the plant from having too little water. “So you can potentially use the vein length per area of fossil plants to make inferences about what the environmental conditions were like where they were growing millions of years ago,” Teischer said. However, vein density and leaf structure are also inherited, and for many species the degree to which these traits vary under different environments is unknown.

Saw greenbrier, Smilax_bona_nox_og, showing veins that Zack Quirk is measuring as part of his research. Credit: Zack Quirk

Quirk’s research centers on sampling vein length per area from a wide range of plant families to see how environment, evolutionary history, and habit (the form of the plant e.g. herb, shrub, tree, etc.) predict vein density. We asked him to explain his work.

What got you interested in studying leaf veins?

Veins are very important for transporting water and nutrients throughout the leaf, as leaves are needed for plants to make their own food via photosynthesis. As such, this leaf characteristic is linked to many physiological plant functions, so I’m interested in determining how these relationships have evolved in living and fossil plants.

What can your research tell us about changes in the environment over time?

Plants are very resilient organisms and have survived many environmentally shifting events, like mass extinctions. My research aims to examine how leaf traits were adapted to environmental and climatic changes in the past and to use these ancient experiments on how anthropogenic climate change will affect living plants. 

The Philadelphia Herbarium at the Academy of Natural Sciences of Drexel University contains over 1.4 million specimens of plants, fungi and algae.

Why is this important?

In the geologic past, plants have persisted through many different climates. For example, middle Eocene (~50 million years ago) plants were in environments with temperatures and carbon dioxide levels much higher than today, but still flourished. With the rate that modern global carbon dioxide and temperature is increasing, we can gain insight on how plants will try to adapt to these changes.

What drew you to the Academy’s herbarium?

The Academy’s herbarium has a substantial collection of plants from around the world. They have many leaf specimens from Pandanales, one of the plant groups that I am studying, so I was interested in viewing these leaves.

Why is the Academy’s herbarium important to your work?

My research is focused on non-woody flowering plants, called monocots. Although these plants are key in global agriculture and ecosystems, they are understudied. The Academy’s herbarium is important to my work because I want to make sure that I have sufficient representation in all of the monocot plant groups that I am studying, so the specimens from the herbarium will greatly help to ensure this aim.

What is your research showing so far?

Although my research is still ongoing, I have found interesting leaf vein patterns in the banana and ginger group (Zingiberales). These patterns indicate that there is a strong link with plant growth form and plant environment in the formation of specific leaf vein arrangements. I am excited to conduct this analysis with other plant groups once I have more data!

By Jordan Teisher and Carolyn Belardo

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In the Academy’s Spotlight on the Collections series, we tell stories about specimens chosen by our scientists and also how researchers and others around the world depend on our collections for issues involving climate change, water quality, evolution, biodiversity and extinction.

To read previous installments in the Spotlight on the Collections series, visit:

The Name’s Bondi, Synodus bondi

Sole Native Pa. Plant Now Extinct

A Fish Detective Story

I Am the Walrus

Down to Bond’s Bird in the Collection

The Real James Bond, Author

Insect Collection Valuable to Society

Gecko Collection: A Vital Resource

Protecting America’s Food Supply

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  1. How we are treating the backwoods of the world is nevertheless a mirror impression of how we are treating ourselves and to each other.

  2. Quirk’s research underscores the resilience of plants and their ability to adapt to changing environmental conditions throughout history. By studying leaf veins, researchers can unlock clues about the past and better understand how plants may cope with future environmental challenges.

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