Hall of Botany

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

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.

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 in 1966: Santa Clauses

Christmas in July…”Santa Claus” floating in the air.

(Or I guess, technically Boxing Day in July, if that’s a thing.)

thistle seed fluff "Santa Claus" in hand

Make a wish!

Have you ever seen fluff floating by in the air, especially in late July, early August? Kids love chasing the fluff around, often referring to them as “Santas” or “Santa Clauses.” You catch it, make a wish, and let them go again, floating away.

dried thistle specimen on herbarium sheet

These are seeds! Most likely thistle seeds, like this specimen here. Or other seeds that have similar “fluff”-like structures. The botanical term for this “fluff” is pappus. Pappus is a modified part of flowers in many species in the sunflower family, Asteraceae (think dandelion). These structures help the seed disperse in the wind, floating away in the breeze, carrying the seed far away. If you’ve tried to catch them, you know they float away in the air very easily. The seeds are small, and often times have already disconnected from the pappus when you catch them.

Check out the “Santa Claus” pappus on this specimen of bull thistle (Cirsium vulgare), collected on July 26, 1966 by Leroy Henry near Woodbine (Butler county), Pennsylvania. Leroy Henry was a botany curator at the Carnegie Museum. All species in the genus Cirsium are known as “thistles.” They have distinctive spiny leaves and stems, with even more distinctive purple flower heads. There are native thistles, but many are introduced. Thistles are common in disturbed areas, and in and around agricultural fields across the country. Bull thistle is native in Europe and Western Asia, but widely introduced across the world, including North America. It is the national flower of Scotland, but the species is considered invasive in many places.

Keep an eye out for thistles, and “Santa Clauses.” Don’t forget to make a wish.

Find this bull thistle specimens here.

Our Eureka Moment!

Searching for rare or endangered plants has become a passion for me. It’s always exciting to find something that hasn’t been seen by very many people. It’s also special when I can share these finds with someone close to me who cares as much about them as I do. I am rather lucky in that my husband, Joe, is also a botanist and shares my passion for finding rare plants. Our household pursuit has even become a bit competitive. I will freely admit, when Joe spots a rare plant first, there is some jealousy intermingled with my excitement that we were in the right place at the right time.

For the last couple of years, we have been on a quest to find Viola glaberrima, a yellow violet last seen in Pennsylvania in 1920, May 30, 1920, to be exact.

I’ve pressed my friend Harvey Ballard, a professor at Ohio University and a renowned Violet expert, for details about habitats to investigate, the characteristics that distinguish the plant from other violets, and any tidbits I could glean to help us find this elusive plant. At least a dozen of my emails to Harvey involved questions about information I’d found in other sources relating to the plant commonly called the smooth yellow violet.

In all honesty, I was suspicious that this violet ever grew in Pennsylvania, even going so far as questioning Harvey about whether he had correctly identified one of the historic specimens. In many ways Viola glaberrima resembles other yellow violets. Pennsylvania has about 30 different kinds of violets, five of which are yellow. The other yellow stemmed violets known to occur in the Commonwealth are usually many stemmed with stems that more-or-less lay down on the ground. These other violets also have either heart shaped or what are termed hastate shaped leaves, that is leaves with outlines reminiscent of a spear point with two points protruding from its base. Many of the plants in this group have flowers that are yellow on the front and back. Some of these flowers develop purple coloring on the back of the petals with age. The violet we’ve been searching for has a single, upright stem with cuneate or wedge-shaped leaves and always has purple on the back of the petals.

Harvey served as a coach for our search for Viola glaberrima, and in doing so he did much more than advise us to look on moist wooded slopes. Many floras list our target plant as merely a variety of Viola tripartita, a flower commonly known as the threepart violet. Harvey assured us that Viola glaberrima is a good species in its own right, and provided additional motivation by making a prediction. He told us that if we found it in the field we would have a “Eureka” moment, because the species is visibly different from the other yellow violets.

Historically, the smooth yellow violet was collected 5 or 6 times in Pennsylvania. The earliest collection is pretty vague, “Mercersburg Pa. in 1845.” The other collections aren’t any more precise. One collection from 1900 is from somewhere “between Ruffsdale and Jacobs Creek in Westmoreland County.” There are two collections from the area of Hillside, PA collected in 1907 and again in 1909. The site we felt we had the best chance of relocating this difficult to find violet was Killarney Park in Fayette County. This seemed to be the most precise locality and the most recent. In May of 1920 Otto Jennings of Carnegie Museum fame and Ernest Gress, a student of Jennings who later worked for the Pennsylvania Department of Agriculture, both collected this violet at this location on the same day. Killarney Park, established in 1909, was a popular place for folks to get out of town and have a picnic or a reunion. It featured a dance hall, lakes for boating, picnic grounds and overnight accommodations. With a stop on the Indian Creek Valley Railroad, the park was easily accessible to rail travelers.

The park property changed hands a few times over the years. Its name changed in 1926 and again in 1939, and it was eventually sold in 1941 to the Christian Church of Somerset for use as a summer camp. Thus, the current name of Camp Christian came into being. In June of 2016, Joe and I spent some time at Camp Christian helping guide field trips for the Botanical Society of America, Northeast Section Joint Field Meeting. I got to know the manager of Camp Christian and told him about the rare violet that had last been collected there. June was a little late, the violets were pretty much done blooming. We looked around for the violet without any luck, but the manager invited us to come back and look anytime. Last year, 2019, we spent parts of two days looking around the property again for the little yellow violet that seemed so elusive.

Most of the violets had already gone to fruit at the time of our 2019 visit, which coincided with the historic collection calendar date of May 30. This year, we visited earlier in May, found many violets blooming, and checked thousands of them without finding a smooth yellow violet.

photo of viola glaberrima showing underside of petals

So, in the process of doing field work and looking for other rare plants, it became a habit for us to look for what seemed to be mythical yellow gems. During a field work day in Indiana County on May 16, while cutting up over a hill to take a shorter route back to the car, we came upon a small patch of yellow violets that were different than any we had seen before. They had single stems, with lance shaped leaves and purple coloring on the backs of the petals. There was no denying that this violet was different than any we had seen before. The plants fit all the characteristics that Harvey had so patiently described for us over the many e-mails. This was finally our promised “Eureka” moment.

Begrudgingly I’ll admit that Joe was first to spot it. (He walks faster than I do.) Of course, Harvey was one of the first people I contacted, I sent him several photographs and to my delight we received the following response: “Hi Bonnie and Joe, YOU NAILED IT!!! You found Viola glaberrima! What a great find! It is likely rare and sporadic along that mountain range. Congratulations. Big ice cream sundaes for you!” How did Harvey know I love ice cream sundaes?

I would love to say this was a “Eureka “moment 100 years in the making, but it was only 99 years and 351 days.

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.

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

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