HEBERLING LAB

Though the supercontinent Pangea broke apart many millions of years ago, the Anthropocene is marked by a new kind of Pangea. Though the seven continents as they are today may not be physically connected into a single landmass, they are perhaps more connected than they have ever been. The globalization of human activities has brought species from around the world into contact which otherwise would never interact. Some species are intentionally moved from one continent to another, such as the plants in gardens, while other introductions are accidental, mere unintentional passengers of human increasingly global activities. Introduced species can fundamentally alter the landscape and are regarded as one of the top threats to native biodiversity.
 
Invasive species are those introduced species which are non-native and spread without human intervention.  Many invasive species alter ecosystem functioning and change regional biodiversity. Invasive plant species have become a common part of our landscape. Some were brought over hundreds of years ago by European colonists. Others have arrived much more recently.
 
In Pennsylvania, the invasion of some plant species are obvious – that is, a unique species arrives, thrives, and become abundant. These invasive species have no record of being in the area and can spread rapidly, sometimes over the course of a human lifetime or shorter. Many invasive species are still actively spreading across the landscape. For instance, garlic mustard (Alliaria petiolata) is a well-known forest herb from Europe introduced to North America in the mid-1800s and after more than a century are now common across Pennsylvania forest. Another obvious example is giant knotweed (Reynoutria sachalinensis), a native to parts of East Asia, first recorded in western Pennsylvania in the 1920s and has since spread to line many of Pennsylvania’s rivers and streams today. You can’t go far in the Pittsburgh region without seeing invasive knotweed.
 
Other species invasions are less obvious. These so called “cryptic invasions” are the introductions of very closely related species or subspecies which originated elsewhere.
 
This specimen of common reed (Phragmites australis) tells the tale of a widespread cryptic invasion. The specimen was collected by Carnegie Museum botany curator Otto Jennings on November 2, 1930 along the shores of Lake Erie at Presque Isle, Pennsylvania. Common reed is a major problematic invasive species, crowding out native species in this unique habitat at Presque Isle. When this specimen was collected over 90 years ago, it was not nearly as abundant as it is now.
 
But is it non-native? Common reed, or often simply called Phragmites, has a very widespread distribution, found in wetlands and shores across all continents except Antarctica. It is even not an uncommon site along wet areas near highways. It is among the most widely distributed plants in the world.
 
Reed is non-native to the United States...well, mostly. In the 1800s, botanists considers Phragmites to be a relatively uncommon plant. Evidence from fossils and paleocological research show that the species has indeed been in North America for many thousands of years. However, it didn’t start to become abundant until the early 1900s and after. Some botanists suggested the sudden success of the species could be due to human disturbance.  A pioneering herbarium-based study 2002 published in the PNAS by Dr. Kristin Saltonstall sequenced DNA from herbarium specimens collected before 1910 and recent collections to show that the spread of Phragmites in the United States was due to the introduction of a non-native strain of the species that originated from Europe.
 
Pretty cool, huh? And this finding was made possible with herbarium specimens.
 
So, is this particular specimen native or not?  I don’t actually know, but with expert examination and genetic analysis, we could find out!
 
Find this specimen and 149 more in the Carnegie Museum herbarium here: https://midatlanticherbaria.org/portal/collections/list.php?db=328&taxa=Phragmites+australis&usethes=1&taxontype=2

A large stand of Phragmites at Presque Isle State Park, Pennsylvania (August 2019).

​Corn is a staple crop known well by many across the world.  Corn is used in a variety of ways including human food (from corn on the cob to corn syrup), animal feed, ethanol production, and especially this time of year, fall decoration and corn mazes. Corn is an economically important crop worldwide, with over 81 acres expected to have been harvested in the US alone this year.  But where did this plant come from?
 
Corn, better known to many as maize (Zea mays), is a domesticated plant.  Yes, plants can be domesticated, just as your pets.  Corn was domesticated from a wild grass species known as teosinte in Mexico approximately 8,700 years ago.  Like many other food crops, corn was domesticated by humans through artificial selection – that is, through selective breeding for traits of interest over many generations, causing the evolution of a species.  In the case of corn, teosinte evolved through human intervention by selecting seed from plants with desirable traits (such as large cobs), planting those seeds, again selecting the “best” plants, and repeating over decades.  Eventually, teosinte evolved from a many branching grass with small seed cobs to what we recognize as corn today – tall, unbranched plants with large, tasty cobs. 
 
This specimen is of a species of teosinte (Zea mays subspecies parviglumis) that is thought to be the close relative of the domesticated crop we know today (Zea mays subspecies mays).  This specimen was collected near the site of domestication in Mexico on October 2, 1982 by Hugh Iltis, a botanist and geneticist at the University of Wisconsin-Madison who studied teosinte species and an influential conservationist.   Note the species name on the label “Zea mays L. subsp. parviglumis var. parviglumis Iltis and Doebley” – his name at the end denotes Iltis was one of the scientists who named the taxonomic variety new to science in 1980. It was also collected in the “type locality,” meaning from the same spot where the specimen used to describe the species was collected. 

​It is now a common plant in forests across Pennsylvania, but it wasn’t always.  This specimen of Japanese stiltgrass (Microstegium vimineum) was collected on September 7, 2017 by Mason Heberling (me!) at Trillium Trail, Fox Chapel, PA.  Native to East Asia, Japanese stiltgrass is an annual grass that is said to have first been introduced accidentally to Knoxville, Tennessee around 1919, used as packing material for porcelain dishes from China.  It has since become a major invasive species, spreading across forests of Eastern North America.  It is commonly found along trails, forest roads, and floodplains.  It has been shown to be facilitated by deer overabundance.  A recent study of unconventional gas well pads (such as “fracking”) in Pennsylvania by Penn State researchers found that recent hydraulic fracturing activities facilitates stiltgrass invasion (Barlow et al., 2017 Journal of Environmental Management).  Japanese stiltgrass is especially common in common disturbed moist forests, where available light in the understory is higher.  Therefore, it often carpets the forest floor in disturbed forests.  High densities of deer have also been shown to facilitate stiltgrass invasions.  In fact, much of this research was done at Trillium Trail by Susan Kalisz (then at University of Pittsburgh, now at University of Tennessee Knoxville).  Read more here: https://kaliszlab.weebly.com/uploads/2/5/1/2/25120034/knightsmithdaviskalisz-na_j2009.pdf   They used fences to exclude deer and found that stiltgrass was not present in fenced plots, but abundant when deer were allowed access. The Kalisz lab actively remains at Trillium Trail.
 
Although collected only two years ago, I was surprised to find that this specimen was the oldest Japanese stiltgrass specimen collected in Allegheny county!  There is a chance it had been collected earlier and exists in another herbarium. It was said to be uncommon (possibly absent) at Trillium Trail until 2002. 
 
What will our forests look like in another 10 years?  Herbarium specimens are important, verifiable sources to document our changing flora.  And ultimately, help conserve our flora.

Once you learn to recognize this grass, you are likely to see it everywhere in forests and forest edges in Western Pennsylvania. It is especially obvious in the Fall, when it flowers and has reached its peak growth. Note the faint white line along the center of the leaf blades.

​Microstegium vimineum carpeting the forest floor outside deer fences at Trillium Trail.  

Although often overlooked, herbarium specimens that were collected in cultivation have important uses. These plants were intentionally planted by humans rather than growing naturally in the wild.  These specimens were collected from farms, gardens, greenhouses, or even those planted in your yard or city parks.  These plant species are often economically important, providing benefits to humans in the form of food, medicine, fibers, or simply beauty.  The Carnegie Museum Herbarium has about 5,736 specimens that are known to be collected in cultivation, dating back to 1817!
 
This wheat (Triticum aestivum) specimen was collected on June 29, 1916 from a farm in Vallonia, Pennsylvania (Crawford County).  This specimen was collected well before the so-called “Green Revolution” of the 1930s-1960s when agriculture changed globally with new plant breeding technologies (high yielding crop varieties), increased pesticide use, and synthetic fertilizer production and use.  
 
Compare this particular wheat specimen (which barely fits on the herbarium sheet; note it is bent 3x to fit) to a much shorter one now on display in the We Are Nature: Living in the Anthropocene exhibit at the Carnegie Museum of Natural History. The specimen on display was collected nearly a 100 years later and is a dwarf variety.  This wheat cultivar was developed through plant breeding technologies in the mid-20th century to improve crop yields.  Semi-dwarf wheat was developed in Mexico in the 40s and 50s through plant breeding efforts led by Norman Borlaug, who later won the Nobel Peace Prize for his work that addressed world hunger through agricultural technologies.  The majority of the world's wheat crop is now a semi-dwarf variety.
 
Herbarium specimens collected in cultivation could provide important information on the types, traits, and genetics of crops grown over the past two centuries, a period of much change.  Are some disease-resistant genotypes or cultivars which no longer exist stored in herbaria? 
 
Another important, yet largely untapped, source of information in these specimens collected in cultivation is the non-native species planted intentionally for ornamental purposes.  Many of our non-native species which are now invasive and causing economic and ecological harm were first introduced intentionally for ornamental purposes. In many cases, information on some of the earliest introductions may be stored in herbaria.  These specimens are ripe for study.
 
Take oriental bittersweet (Celastrus orbiculatus) as an example.  Oriental bittersweet is a woody vine from East Asia, now a problematic invasive plant found throughout the Pittsburgh region and beyond.  It became particularly abundant in our region in the 1980s, now common to forests and roadside woods.  Interestingly, the oldest specimens collected in Allegheny County are not from the wild, but instead grown in cultivation in gardens.  Two specimens grown near Highland Park collected in 1916, followed by another specimen collected 34 years later (also in cultivation!).  It was not collected outside of a cultivated setting in the county until 1979.  And now, it is ubiquitous!  What insight can those first specimens collected in cultivation in 1916 tell us?  Were these the source of introduction? And more importantly, can they provide information on basic invasion processes to help us prevent future invasions by other species? 
 
Specimens collected in cultivation may be seen as “not natural” or otherwise less important than those collected in natural areas or found spontaneously growing without direct human intervention.  But it is clear that specimens collected from cultivation have an important role to play.  We must continue to record and archive cultivated species in natural history collections.  After all, human impact and the blurring of “nature” and “human-made” is the hallmark of the current era, the Anthropocene, so cultivated species document nature just the same way as “wild” occurring plants.

Herbarium specimens provide key insights into the Anthropocene.  In many cases, natural history collections are the only baseline we have to understand the widespread, complex effects of human activities on the earth systems over the past century.
 
This grass species shown here is of particular interest.  This specimen was collected in Cambridge, England on June 18, 1829.  This grass species (Alopecurus myosuroides), commonly known as “slender meadow foxtail” or “black-grass,” is a major weed in farm fields (especially wheat and barley), and can significantly reduce crop yields.
 
Unwanted plants (“weeds”) have been an ongoing fight for humans since the dawn of agriculture.  The  “Green Revolution” (1930s-1960s) was a point in human history when agricultural production increased at an enormous rate and at unprecedented scale, aided  by technological developments in crop breeding, pesticides, herbicides, and fertilizers.  It has been one time point suggested to mark the "official" start of the Anthropocene, a proposed geological era defined by human activities.
 
Herbicides are commonly used to control weeds to increase crop yields.  With the increase of herbicides, some plant species have evolved resistance to these herbicides. In a cool study in PLoS ONE in 2013, Délye et al. did a DNA analysis of herbarium specimens collected from 1788 to 1975 to show that some individuals of this grass species already possessed the gene mutations associated with herbicide resistance well before herbicides were widely used!  They show that the use of herbicides selected for these individuals, such that those individuals with herbicide resistance are now more abundant.
 
Who would have thought these specimens would be used this way?  There are so many known and yet to be known uses of herbaria.
 
The collector of this specimen back in 1829 certainly didn’t think it could be used to understand the evolution and effects of herbicide use over 175 years later!
 

Now it's a common forest invader in Pennsylvania, but it wasn't always. Collected on November 17, 1949, this specimen was found by Bayard Long in Delaware.  Native to East Asia, Japanese stiltgrass (Microstegium vimineum) was introduced by accident to Knoxville, Tennessee around 1919, used as packing material for porcelain dishes from China.  It has since become a major invasive species, spreading across forests of Eastern North America.  It is commonly found along trails, forest roads, and floodplains.  It has been shown to be facilitated by deer overabundance.  A recent study of unconventional gas well pads (such as “fracking”) in Pennsylvania by Penn State researchers found that recent hydraulic fracturing activities facilitates stiltgrass invasion (Barlow et al., 2017 Journal of Environmental Management).  You can read more on that research here.

Japanese stiltgrass was introduced more recently compared to many other troublesome invaders.  It only became common in western PA in the past few decades.  In fact, to my surprise, there weren't even any specimens in the museum's herbarium from Allegheny County (Pittsburgh area)!   (But there are now).

Images below: Japanese stiltgrass invading a forest understory in Fox Chapel, near Pittsburgh, PA.