Section of Botany

October 21, 2020 by wpengine

Collected on This Day 98 Years Ago

Chestnuts (used to be) on Chestnut Ridge

And across the entire state of Pennsylvania.

American chestnut (Castanea dentata) was once a very common tree, native from Maine to Mississippi. In the heart of the Appalachians, the historical range covered the entire state of Pennsylvania. I say “historical” and “once a very common tree” because it is no longer. You may occasionally stumble upon an American chestnut tree, especially small trees and saplings persisting as sprouts from the large trees that graced our landscape a century ago. Older trees, with mature fruits, are quite rare.

In fact, some estimates suggest American chestnut accounted for one in four trees in some forests! So, what happened? In the early 1900s, a disease caused by a pathogenic fungus (Cryphonectria parasitica) was accidentally introduced with imported Asian trees. It was first recorded in New York City in 1904. In a matter of decades, American chestnut was nearly decimated by this disease known as Chestnut blight.

The Carnegie Museum of Natural History herbarium captures this change in our forests.

American chestnut specimen on herbarium sheet

This specimen of American chestnut was collected by influential Carnegie Museum curator Otto Jennings on October 21, 1922 on a field trip of the Botanical Society of Western Pennsylvania to Chestnut Ridge, near Derry Township, Pennsylvania. Chestnut Ridge is a ridge of the Allegheny Mountains, presumably named for its (once) many American chestnuts.

This specimen is from the fruit collection of the herbarium. These specimens are different than the “standard” pressed flat specimens on paper. Instead, they are stored to maintain their three-dimensional structure.

Note the note made by Jennings on the label on this specimen: “Trees from ¼ to all killed by blight.”

The case of the American chestnut is an interesting one. It served important cultural and ecological roles; some even calling it a “keystone” species. There is no doubt that the functional extinction of American chestnut ricocheted through the ecosystem, causing long-term biological changes. Many of these changes we may not know. Yet, at the same time, despite the species importance, our forests continue. Presumably other species have filled the functional and physical space of American chestnut.

Disease and pest outbreaks in Pennsylvania’s forests continue. Many of our critical tree species are likely to decline in coming years and decades. Some iconic species have already declined or are at risk. These include our ash species (mortality caused by introduced Emerald Ash Borer), American beech (Beech leaf disease, Beech bark disease caused by an introduced scale insect), and eastern hemlock (mortality caused by introduced sap sucking bug, the hemlock woolly adelgid)…to name only a few threats.

What will Penn’s woods look like in another 100 years?

Our collections document the past and present to inform our decisions for the future.

Find this American chestnut specimen here (along with 268 others!): https://midatlanticherbaria.org/portal/collections/list.php?db=328&includecult=1&taxa=Castanea+dentata&usethes=1&taxontype=2

Check back for more! Botanists at the Carnegie Museum of Natural History share digital specimens from the herbarium on dates they were collected. They are in the midst of a three-year project to digitize nearly 190,000 plant specimens collected in the region, making images and other data publicly available online. This effort is part of the Mid-Atlantic Megalopolis Project (mamdigitization.org), a network of thirteen herbaria spanning the densely populated urban corridor from Washington, D.C. to New York City to achieve a greater understanding of our urban areas, including the unique industrial and environmental history of the greater Pittsburgh region. This project is made possible by the National Science Foundation under grant no. 1801022.

Mason Heberling is Assistant Curator of Botany at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

How Do You Preserve a Giant Pumpkin?

giant pumpkin being moved with a forklift

A few years ago, I came across a dilemma that I wasn’t sure how to resolve. The Section of Botany was given permission to preserve, for the scientific collection, part of the giant pumpkin that was in the exhibition, We Are Nature: Living in the Anthropocene. This was an intriguing offer. I just wasn’t sure how to go about it. Preserving any large fruits or plant parts can be a real challenge. Plant materials must be dried before they rot, and the process must happen at a temperature low enough to prevent the material from being cooked. The normal procedure of putting a plant or plant part into a plant press and drying it with warm dry air was not really an option; at least not for a 2,090-pound pumpkin that wouldn’t even fit in my car, let alone my plant press.

Pumpkins are a type of squash, but trying to literally squash one to dry it seemed a bit daunting. The farmers who grew this giant pumpkin were more than willing to give us whatever parts of the pumpkin we wanted to preserve, and they were even willing to help with cutting them from the pumpkin. We decided on trying to keep the unique parts of the pumpkin, like the stem and the blossom end (bottom). We also saved some of the inner tissue and a few seeds. The seeds on a pumpkin this large are a prize commodity. If a pumpkin from which seeds are properly harvested was a champion, as this one was, each seed could sell for $30 to upwards of $50. It was very generous of the farmers to allow us to have some of these seeds for our collection.

dried pieces of a pumpkin on an herbarium sheet

Pumpkin farmers keep close tabs on the genetics of these giants and actively work at growing larger pumpkins. You can actually find family tree information for this very pumpkin online if you search for it. Who knows how large mankind will eventually enable pumpkins to grow? The plants that grow these large squashes (the Cucurbita maxima variety known as ‘Atlantic Giant’) are a variety of the same species that produce Hubbard Squash. This species, which was originally from South America, has become one of the more diverse domesticated plants.

Giant pumpkins have been a focal point of imagination and literature for some time. Think of Cinderella. There are several variants on the Cinderella tale going back hundreds of years that involve large squash. Back when these stories were written though, it was a fantasy to think there actually could be a pumpkin that a person could fit inside.

Now that we are using QR codes on our herbarium labels, it’s easy to add photographs to plant specimen records. I wish we had thought to do this before the massive pumpkin was cut up. Maybe I will go back and add a QR code to the label, so the actual pumpkin can be seen again in its full glory. What we have in the collection now are bits and pieces, mere remnants of the gentle giant that grew 45-50 pounds per day in 2017.

Getting back to my original question, how do you preserve a giant pumpkin? I guess the answer is a little bit at a time!

More on this giant pumpkin:

Sasquatch Squash

Giant Pumpkin Seed Harvest

Collected on This Day: November 25, 2017

Bonnie Isaac is the Collection Manager in the Section of Botany. Museum staff, volunteers, and interns are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

September 29, 2020 by wpengine

Collected on this Day in 1967: Fall blooms rival those of spring

photo of aster flowers with white petals

In the northeastern United States, we often think of spring as a time for wildflowers. But the fall is, too.

It is easy to be distracted by the beautiful fall foliage, when our landscape turns brilliant shades of red, orange, and yellow. But when many plants are shutting down for the winter, others are just kicking into gear.

Many wildflower species bloom well into fall, both in open areas and in the forest understory. One group of plants are the fall blooming “asters.” In same plant family as sunflowers and dandelions (Asteraceae), Aster was once a very large plant genus in our native North American flora (somewhere along the lines of >175 species!), but as we learned more about the evolutionary relationships of these plants, they have since been split into multiple genera (plural of genus). In fact, there is only one “true” Aster in Pennsylvania, Tatarian aster (Aster tataricus), which is actually not even native to Pennsylvania! Regardless of the scientific name, these plants are commonly referred to as asters. And they put on quite an autumn show in Pennsylvania.

dried specimen of aster flower from Carnegie Museum of Natural History herbarium

Perhaps one of the most common woodland asters in Pennsylvania is white wood aster (Eurybia divaricata, formerly known as Aster divaricatus). This specimen was collected September 29, 1967 by N.R. Farnsworth in Pittsburgh’s Schenley Park. This species can still be found in Schenley Park, and many parks, woodlands, and wooded roadsides across Eastern North America.

Fall foliage is beautiful in Pennsylvania. But don’t forget to look down at the flowers, too!

Find this white wood aster specimen here: https://midatlanticherbaria.org/portal/collections/individual/index.php?occid=11826562

Herbarium specimens hold more information than we realize

The first herbarium I visited was the Pringle Herbarium at the University of Vermont as part of an undergraduate class on plant taxonomy and systematics. Prior to this visit, I assumed herbaria were fairly mundane collections of dead, dry, flattened plants, and that they couldn’t possibly interest me as much as emerald-green plants thriving in the wild. However, within moments of entering the Pringle Herbarium, I was captivated by the football-sized cones of the sugar pine (Pinus lambertiana). These giant cones, of a species native to mountain slopes in California and Oregon, were the largest of any gymnosperm I had seen at that time, and I quickly discovered that herbaria were fascinating resources for studying plant diversity around the world.

Plant specimens capture important information on plant traits across species, continents, and centuries. With over 390 million specimens worldwide and becoming increasingly available online (500,000 specimens at Carnegie Museum alone), that’s a lot of potential information! We found that measurements using herbarium specimens strongly correlate to those measured in the field, including two leaf traits and one stem trait.

Years later as a graduate student interested in plant functional ecology, I was reminded of the diversity contained within herbaria, but learned that herbarium specimens were rarely used to study plant functional traits. Functional traits are characteristics that provide ecologists with information about growth, reproduction, or survival strategies, and in plants they are often measured using living tissue. For example, three commonly measured functional traits are specific leaf area, wood density, and leaf thickness. Specific leaf area (equal to the fresh area of a leaf divided by its dry mass) indicates how much dry mass plants invest in their leaves, a factor coordinated with their rate of photosynthesis. More specifically, plant photosynthetic rates tend to increase the bigger leaves get relative to their dry mass. On the other hand, wood density is used to understand carbon storage, which is important for studying carbon sequestration and climate change. Leaf thickness can help understand leaf thermoregulation, herbivory, and gas exchange. Currently, it’s unclear if herbarium specimens can provide reasonable estimates of these traits, but if so herbaria can vastly expand our understanding of plant functional diversity.

Recently, I teamed up with scientists Jessica Rodriguez and Dr. Mason Heberling (Assistant Curator of Botany at Carnegie Museum of Natural History) to understand if and to what extent herbarium specimens could be used as proxies for functional traits collected from fresh plant tissues. In our study just published in the American Journal of Botany, we found that herbarium specimens can provide accurate estimates of specific leaf area, branch wood density, and leaf thickness. Although drying plant tissues may lead to some inaccuracies in functional traits that are typically measured using fresh tissues, our study suggests the dead, dry, flat plants I once considered uninteresting could rapidly advance what scientists know about plant functional diversity. Importantly, our research highlights herbaria as rich sources of functional trait data with the potential to accelerate the study of important ecological processes like species responses to climate change.

Timothy M. Perez, Ph.D. is a postdoctoral scholar at the University of British Columbia whose research focuses on plant heat tolerance and the conservation of plants in the tropics.

The circle of life… and invasion

If you have a garden in Pittsburgh, chances are that it has been invaded by nonnative plants. Nonnative plants are species that have been introduced by humans to a location outside their native range. Typically this means that humans have carried a species across oceans or mountains or very long distances that the species would be unlikely to travel on its own. This includes dandelions (Taraxacum officinale), English ivy (Hedera helix), garlic mustard (Alliaria petiolata), Japanese knotweed (Fallopia japonica), and thousands more. In many cases, nonnative, invasive species hurt our efforts to protect and restore natural areas by displacing native plants from their environment and reducing the healthy functioning of ecosystems.

As an invasion ecologist at the University of Pittsburgh, I aim to identify the traits that make nonnative plants unique from native plants and investigate how these traits influence a nonnative species’ ability to invade and persist within ecosystems. I’ve become fascinated by one plant trait in particular: phenology, or the timing of a plant’s life cycle events, like flowering in the spring or leaves changing color in the fall. Phenology is critical to the survival and reproduction of all organisms. Plants, for example, need to be able to germinate at the exact right time in the spring; early enough to maximize their growth potential, but late enough that they avoid damaging winter frosts. Plants must also flower and set fruit at a time when their chances of reproduction are highest, such as when pollinators are the most active, or when seeds are most easily dispersed. The timing of phenology also impacts a plant’s ability to compete with other species. An older, mature plant is likely to be a better competitor than a newly germinated seedling. As a result, most species have evolved to become sensitive to a wide array of environmental factors, including temperature and precipitation, which signal the “ideal” time to enter into a new stage of the life cycle.

dried plant specimen with purple flowers

dried plant specimen with yellow flowers

In a recently published study, I partnered with Dr. Mason Heberling and Bonnie Isaac at the Carnegie Museum of Natural History to explore how phenology differs between native and nonnative plant species. Plant specimens from the museum’s herbarium provide us with valuable snapshots of phenology from more than the past 120 years. By looking at a specimen’s collection date and identifying reproductive structures on the specimen (did the plant have open flowers or fruits?), we can determine the annual timing of life cycle events for a species and compare it with other species throughout time.

First, our research team asked: are there differences in the timing of reproduction between native and nonnative plant species? We referenced nearly a thousand herbarium specimens that were collected in old-field ecosystems (i.e. abandoned agricultural fields) since 1900. We found that nonnative plants reproduce substantially earlier than native plants in old-field ecosystems. Specifically, nonnative plants flowered 50 days earlier, and set fruit 17 days earlier, on average, than native plant species. When considering that the growing season in western Pennsylvania only lasts for 121-180 days in total, this is a very large difference in the activity periods of these species! We predict that the early reproduction of nonnative plants may actually help them to survive in invaded ecosystems, and my current research is experimentally testing some of these ideas at the Unviersity of Pittsburgh field station. I hypothesize that nonnative plants are accessing important resources, like soil nutrients and light, by growing and reproducing earlier than native plants.

We also found that all old-field species, regardless of origin, are flowering approximately 10 days earlier, and fruiting 13 days earlier today than they were at the beginning of the 20^th century. What is causing plant species to shift their phenology over time? This is likely a response in-part to climate change, which has caused warmer and wetter springs in Pennsylvania

Next, we asked: are there differences in the sensitivity of native and nonnative phenology to climate signals? Sensitivity is defined as the number of days a plant will shift the timing of reproduction in response to a change in the environment. For example, a species with “high” sensitivity to temperature might flower several days earlier than normal in response to a particularly warm spring. By contrast, a species with “no” sensitivity to temperature will flower at the same time every year, regardless of temperature. To answer this question, we paired plant specimens from the CMNH herbarium with historic climate records that date back to 1900. This source tells us the temperature and precipitation conditions for each month and year that a specimen was collected. Our study found that native and nonnative species are not sensitive to the same types of climate signals. When looking across a range of temperature and precipitation signals, the timing of reproduction in native plants often would shift by a different number of days than in nonnative plants. This information may be important in helping scientists to understand how plant phenology will respond to future climate change: Will native and nonnative species respond similarly, as seen in the past, or will their responses begin to diverge?

Herbarium collections such as those found at the Carnegie Museum of Natural History provide invaluable insight into the traits of species throughout history. We hope that, through the continued exploration of these data sources, scientists will continue to uncover new findings about the relationship between invasion, plant phenology, and climate.

Rachel Anne Reeb is a PhD candidate at the University of Pittsburgh.

Protecting Plant Specimens from Decomposing

It takes a lot of time and care to keep our collections and specimens out of harm’s way. A TikTok viewer asked us on a video of mounting a herbarium specimen, “How do you protect it from decomposing?” and we sought to answer that question, but it would certainly take more than 150 characters. From start to finish, the process can take anywhere from 7 days to weeks, depending on the amount of specimens that we receive. We have roughly 533,000 specimens, and that number continues to grow. Here’s a look at what steps we take to ensure they will last and be preserved for use in the future.

First, we press the new fresh plants between sheets of newspaper and corrugated cardboard and use cam straps to bundle them as tightly as possible.

cardboard, wooden boards, and red cam straps

We dry them rapidly with a box crafted by Bonnie and Joe Isaac. A small space heater forces warm dry air between the pieces of cardboard. The quick drying is essential to preserving the colors of plants we collect. Quick drying also makes it less likely a plant specimen will rot, mold, or have browning of leaves than if it were just drying at room temperature for several days or weeks. Our method usually dries them in 72 hours or less.

box setup for quick drying of plant specimens

side view of box setup for quick drying of plant specimens

After they are pressed, we place the specimens in a freezer for at least 24 hours. This will be their first freeze: it is done to get rid of any living pests that may be hiding in the material.

Next, we mount dried plant specimens onto cotton fiber neutral pH archival acid free paper. The basic Elmer’s glue we use to stick the specimens to the paper is also acid free and good for archival use, as well as the paper and ink used on the data labels. After they are mounted, they will meet with the freezer for at least another 24 hours, assuring any pests that were able to survive the last freeze will be eliminated.

mounting tools: Elmer's Glue-All, archival pen, Glue Stic

Their data are then entered into our database, and we take high resolution photos so that we can post the images alongside their data for use.

Finally, the metal cases we store them in are light tight and airtight, preventing exposure to UV light, insects and pests, humidity, water, and in some cases fire damage. UV light can be the most harmful to the fading and quality of specimens. The longer things are on display the more faded the colors can become, which is part of why behind the scenes collections are so important.

open cabinet full of stacked plant specimens

Maintaining and protecting the collections that we house is a full time labor of love. You see these specimens through so many steps and look closely at each item. You learn their names, their attributes, where they are from, and you share these tiny joys with everyone else when you are able to display these beautiful works of nature and art. So maybe another answer to the question “How do you protect it from decomposing?” is… you just love it a little extra.

Sarah Williams is Curatorial Assistant in the Section of Botany at Carnegie Museum of Natural History. Museum employees are encouraged to blog about their unique experiences and knowledge gained from working at the museum.

Collected on This Day 98 Years Ago

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