U of A Herbarium documents and preserves the plant biodiversity of the Sonoran Desert

It may seem shocking, but the Sonoran Desert happens to be one of the most biologically rich desert ecosystems in the world. Southern Arizona is home to thousands of unique plant species that have evolved to be able to thrive in this hot, dry climate. Preserving and documenting this biodiversity in facilities like the University of Arizona Herbarium is critical for both research and conservation efforts, as many of these species are facing inevitable pressure from shifting environmental conditions.

The U of A Herbarium is directed by Michelle McMahon, an associate professor of practice in the School of Plant Sciences. She describes her journey to a career in plant sciences as circuitous, with stops studying electrical engineering, evolutionary biology - and even spiders - before finding her passion to understand the incredible complexity of plants and the impact they have on our planet. Aside from serving as the director of the Herbarium, McMahon teaches courses related to phylogenetics, biodiversity and the evolution of plants.

What is the Herbarium, and why is having one important in Arizona?

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The U of A Herbarium is a natural history collection that is dedicated to preserving and documenting plant biodiversity. The Herbarium is home to nearly 450,000 specimens of plant material that are used for a variety of different purposes, some going back more than 170 years. These specimens are dried, pressed plants that are precisely labeled with information about when and where they were collected and are accessible to members of the research community and the public. We provide the expertise that goes along with understanding plant biodiversity in our area. The Herbarium offers educational opportunities through workshops and classes for those looking to learn more about plant life.

Arizona has a particularly unique and diverse set of ecosystems, especially in the Sonoran Desert. The long-term record of plants at the Herbarium helps researchers, the public, and land managers understand what species are present and how ecosystems function in plant communities as they change over time.

How has the Herbarium’s collection assisted in research and discoveries since its start in 1890?

There is no shortage of research and discoveries that the Herbarium has played a role in over its more than 130 year existence. Currently, there is a project underway that uses the Herbarium’s resources to look at how Earth’s changing climate affects rapid evolutionary response in plant species. Other researchers are looking for metal traces in plant tissues by analyzing the Herbarium’s specimens. Essentially, everybody that studies plants and plant relationships uses the Herbarium in one way or another. For example, if there’s a plant related poison incident, we are the people that poison control calls. The Herbarium also supports producers and landowners. If they have livestock that becomes ill, we help identify the cause if it’s related to plant material.

Why is documenting and preserving plant biodiversity important now more than ever?

The documentation and preservation of plant biodiversity is essential for many reasons. One obvious reason is that we’re losing that biodiversity to changes in land use. Infrastructure is being put up and land is getting plowed, taking with it species that are part of Southern Arizona’s unique ecosystems. We have around 4,000 different plants in Arizona, and their distribution and ranges aren’t always well known. So, if we don’t document what’s here right now, we might miss out on it due to changes in land use. Another important reason is our changing climate, which is altering how, where, and when the plants are flowering. Changes in climate directly affect conditions of plant phenology, which is essentially the timing of life events across different organisms. Documenting plant life at the Herbarium is an essential step towards mitigating those changes.