Mason Heberling

Knotweeds collected at the 7th Annual Knotweed Festival in Blairsville, Pennsylvania.
Banks along Conemaugh River, August 11, 2018.  
Left: Giant knotweed (Fallopia sachalinensis); Right: Bohemian knotweed (Fallopia x bohemica).

​A few weekends ago, I went to the 7th annual Knotweed Festival in Blairsville, about 40 miles east of Pittsburgh in Indiana County.  Aside from reading a brief advertisement, I knew little about the festival before going. But, given I study non-native plant invasions, I had to go to a celebration named after a local weed that is a focus of my research! And this invader is one of the most aggressive and widespread ones in western Pennsylvania – Japanese knotweed.
 
Native to East Asia, Japanese knotweed (Fallopia japonica) is a large herbaceous perennial that was first introduced as to the U.S. in the late 1800s as an ornamental.  As its name suggests, it eventual spread well outside of gardens to become a major nuisance. More troubling, the spread of the species displaces native vegetation and disrupts the natural function of the ecosystem.  The plant has thick hollow stems that somewhat resemble bamboo, although they are not related (knotweed is in the buckwheat family, Polygonaceae; bamboo in the grass family, Poaceae).  Knotweed spreads through persistent belowground structures called rhizomes (belowground stems), as well as by seed.  Small fragments of rhizomes can be washed downstream and easily establish, often forming dense stands along Pittsburgh’s many streams and rivers. Knotweed is among the most economically and ecologically problematic invasive plants in Pennsylvania.
 
So, why name a community festival after this invasive plant?!  Despite the dislike for the plant, the community of Blairsville named the festival partly as a tongue-in-cheek sentiment for the plant that has taken over the landscape and partly to recognize the weed as embedded into the local culture. The nearby Conemaugh River that runs throughs Blairsville has been transformed by this non-native species, completely covering the banks with stands so dense they completely block the view of the river along the community recreational trail.

My family and I had a great time at the festival, visiting local craft and food vendors, musicians and other entertainment, a monarch butterfly display, and complete with a parade.  I even bought soap made from the rhizomes and stems of knotweed collected by the river. 

​ At first, I had mixed feelings about naming a festival after an aggressive invasive plant known to cause ecological harm. On one hand, it embraces the nature around us – whether we like it or not, non-native plants are part of the landscape around us. The global movement of plants around the globe is one of the defining features of the Anthropocene, the current era of pervasive human influence on the environment and Earth’s systems. But, on the other hand, naming a festival after an invasive species normalizes plant invasions and perhaps even embraces the change to the landscape as a good thing.  Despite my initial mixed feelings, I think the festival is a great community gathering that has the potential to raise awareness about the presence of the invasive plant in our community, its ecological effects, and in turn, nature around us (native and non-native).
 
It turns out there are more than one species of invasive knotweed in western PA: Japanese knotweed (Fallopia japonica), Giant knotweed (Fallopia sachalinensis), and a hybrid between the two species, Bohemian knotweed (Fallopia x bohemica).  The hybrid was only recognized in the past several decades and likely originated when these two species “met” after they were introduced in Europe.  The three species are visually similar.  Giant knotweed can be distinguished by its large (usually much larger than your hand), heart-shaped leaves. Japanese knotweed and the hybrid Bohemian knotweed are much more difficult to distinguish, with much variation in leaf shape.  Japanese knotweed tends to be rounder in shape, while the Bohemian knotweed is intermediate between the other two species in leaf shape and size.  The leaf hairs are sometimes the only definitive identifying feature.

​While I was at the Knotweed Festival, I collected some knotweed specimens for the Carnegie Museum’s herbarium. Along the Conemaugh River in Blairsville, I collected both the Giant knotweed and Bohemian knotweed (the hybrid).  But, I did not find any Japanese knotweed. (I suspect my knotweed soap is actually made from Giant knotweed, after all.)
 
The earliest herbarium specimens from Indiana County were collected in 1952 along the Conemaugh River in Saltsburg (not far from Blairsville).  Interestingly, these specimens were of Giant knotweed and Bohemian knotweed – the same species I collected.

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!
 

Deer don’t just eat your garden, they eat native wildflowers too. That in of itself is not a problem.  After all, white tailed deer (Odocoileus virginianus) are native to Pennsylvania.  Deer in PA were once hunted to local extinction, having to be reintroduced.  But deer are now well beyond historic densities.  There are many reasons for this, including land use change (deer do well in forest margins resulting from forest fragmentation), absence of major predators (like the mountain lion, which is now extinct in PA), abundant food sources (like your garden and farms), and hunting management practices.  Deer management is a controversial topic, both for ethical reasons and for competing interests (e.g., managing deer herds for trophy hunting vs. maintaining historic levels for forest management).  The high densities of deer in PA has many consequences ranging from public health (disease carriers esp. tick-borne diseases), car accidents that result in human injury (and higher in car insurance rates), as well as the many ecological consequences (declines in native wildflowers, changes in forest tree composition and forest regeneration, and facilitation of non-native, invasive plants, to name a few).
 
But how do we really know the effects of deer overabundance?  Some impacts are quick, but many others result from chronic deer overabundance.  Long term deer exclosures provide one method to study the effects of deer on the landscape (monitoring fenced forest plots paired with unfenced plots).  These studies are important, but require maintenance and few date to more than a few decades.
 
A recent study introduced a method to measure the effects of deer overabundance using herbarium specimens in Quebec (Canada).  Marie-Pierre Beauvais and others paired historic herbarium specimens (dating back to 1848!) of the large flowered, white trillium (Trillium grandiflorum) with recent observations to find that plants in sites today (with deer) have significantly smaller leaves than those of herbarium specimens.

Read the abstract of the study here:  http://www.nrcresearchpress.com/doi/abs/10.1139/cjb-2016-0206#.WwLeZakh3OQ
 
This study shows the potential of herbaria as time capsules to understand the direct and indirect effects of human activities on our environment.  There is so much knowledge in these specimens waiting to provide insights into the Anthropocene.
 
The specimen of White trillium (Trillium grandiflorum) below (left) was collected on May 21, 1908 by Carnegie Museum of Natural History Botany curator Otto Jennings in Washington County, PA. 
 
Note the specimen on the left, collected in 2005.  I admit this particular comparison only shows two specimens at two time points (too small a sample size to be meaningful on its own) and is cherry picked, but I show these just to illustrate the immense potential to measure hypothesized changes in our plants as a result of human induced environmental changes.  I hope someday to follow up on the cool 2017 study by Beauvais and others using specimens to study changes in the flora western Pennsylvania as a result of historic and recent changes in our deer populations. 

​Keep an eye out for these bright yellow flowers blooming now along creeks across southwestern Pennsylvania. This specimen of lesser celandine (Ficaria verna, formerly known as Ranunculus ficaria) was collected in Edgeworth, Pennsylvania along Little Sewickley Creek by Myrta Macdonald and Jane Konrad in April 18, 1986. Native to Europe, lesser celandine was likely first introduced to the United States into gardens for ornamental purposes.  It is a spring ephemeral, meaning it blooms early in the spring and goes dormant by summer. Lesser celandine is among the earliest species to bloom in the spring, with bright yellow flowers.  In the past several decades, this species has become more and more common in southwestern Pennsylvania.  It grows in open woods, especially in moist soils along streams.  It forms dense mats that carpet the ground, capable of choking out native plants. 

Specimen below: Lesser celandine specimen from its native range in England, collected on April 13, 1826.

​Invasive lesser celandine is easily confused with the native wetland plant, marsh marigold (Caltha palustris).  Marsh marigold is found in somewhat similar habitats and has a similar appearance as lesser celandine.  However, there are several major differences.  Most notable, marsh marigold does not form dense, continuous mats along the ground, but instead plants are distinctly separate (although can be large and robust).  Also, lesser celandine has tuberous roots, while marsh marigold does not.  Compared to lesser celandine, marsh marigold is found in wetter habitats, has fewer flower petals (5-9 in marsh marigold vs. >8 in lesser celandine), and has larger leaves that are more rounded.

Specimen below: Be careful not to confuse lesser celandine (Ficaria verna) with the Pennsylvania native wetland species, marsh marigold (Caltha palustris).  This marsh marigold specimen was collected on April 28, 1887 in Westmoreland county, PA by P.E. Pierron.  The herbarium of St. Vincent College (Latrobe, Pennsylvania) became a part of the Carnegie Museum herbarium in 1991. 

We humans have moved plant species around the world at unprecedented scales. Human-mediated species introductions are a signature of the Anthropocene. Some of these non-native plant introductions were intentional, in the case of ornamental or food plants.  And some of these plant introductions were accidental, often in the case of “weeds” associated with human disturbance, cities, and/or agriculture. When introduced plants can survive and sustain a population without human intervention, we call these species “naturalized.”  When naturalized species are capable of reproducing at high rates and spreading across the landscape, far from the point of introduction, we call these species “invasive.”  This process from introduction to naturalization to invasion can occur quickly, but in many cases, there is a lag such that species introduction to full blown invasion can take decades to realize.
 
Herbarium specimens play a critical role in understanding species invasions, serving as a valuable archive of introduced plants.  When were species first introduced? Were they first introduced accidentally or were they intentionally planted in gardens? Where were species first introduced? Were they introduced multiple times at multiple locations? How have these introduced species spread in the decades to centuries since introduction? Have their morphology or genetic makeup changed since introduction?  Which introduced species become naturalized, which become invasive, and which species fail to establish altogether? These are just a few of the many questions that can be answered using herbarium specimens. 

​Some species are well adapted for life in the Anthropocene, commonly found in novel, human-made habitats such as roadsides, sidewalk cracks, farm fields, dumps and industrial sites.  One such plant species that particularly well suited to city life is “quickweed” (Galinsoga quadriradiata). It has many common names, including “Peruvian daisy,” “shaggy soldier,” and “fringed quickweed.” In fact, the species was once known locally as “Pittsburgh weed.” To our knowledge, this is the only example of a non-native species that was first recorded in North America in Pittsburgh (or at least among the earliest). It was introduced here from South America sometime in the mid-1800s.  Pittsburgh weed was first discovered by the courthouse in Pittsburgh by Judge John D. Shafer (1848-1926), a prominent lawyer and dean of Law School of the Western University of Pennsylvania (now University of Pittsburgh). An avid botanist, Shafer was also a founding member of the Western Pennsylvania Botanical Society. The specimen pictured here is one of the earliest (if not the earliest) specimen collected in North America, well outside its native range. It was collected 1869 in along the “Ridge St” railroad tracks in Allegheny City, which has since been annexed by Pittsburgh (now the North Side).  Keep a look out for this interesting species throughout the city, especially along sidewalk cracks and at the base of street signs and electric line poles.  It is now a common weed, and can be found in nearly every major city all over the world.

Below: Close up of original specimen label from the earliest collection (that still exists) of the species in Pittsburgh, collected in 1869.

Below: "Pittsburgh weed" (aka "quickweed") taken on October 13, 2017 in the lawn near the Carnegie Museum of Natural History.

Even though it was collected in Japan, this specimen might look familiar in Pennsylvania. This specimen of wintercreeper (Euonymus fortunei) was collected by M. Togashi in Japan in 1985. Native to East Asia, wintercreeper (also called Fortune’s spindle or climbing euonymus) was introduced to North America in 1907 for use as a ground cover.  In fact, it can be found just outside the Carnegie Museum, around the parking garage.  It can escape cultivation, to establish and become naturalized (sometimes invasive) in the Eastern United States.  Wintercreeper is a fast-growing woody vine which has evergreen leaves.  Wintercreeper is recognized as invasive by the Pennsylvania Department of Conservation and Natural Resources (PA DCNR), with potential to cause ecological harm in natural areas (link).
 
Herbarium specimens are valuable resources to study invasive species -- not only to monitor changes through time (since introduction) and to track its spread across the US, but also to compare to populations growing in the native range.  Much untapped potential in herbaria worldwide for understanding species invasions.

Stumbled upon this neat little book from 100 years ago in the Botany library, which promotes the use of this plant as an ornamental.  The book was published in 1917, ten years after wintercreeper was introduced to the US.  Many states (including PA) now recognize this species as problematic or having the potential to become invasive.  [note: Evonymus radicans is a synonym for Euonymus fortunei var. radicans]

Below: Euonymus this morning outside the museum.  Probably not much photosynthesis happening this winter morning, given it is 0 °F (feels like -18°F​)!