Mason Heberling

This specimen of Callery pear (Pyrus calleryana) was collected on October 11, 1979 by W.Z. Fang in Jiangsu, China. Callery pear is native to East Asia (China, Vietnam).
 
But...Callery pear can be found in the United States. It was (and is) widely planted as an ornamental landscape tree.  Along streets, in residential yards, in parking lots  - it was a prized plant for well-groomed anthropogenic landscapes. It uniformly grows in low resource conditions, explodes with many beautiful blossoms each spring, provides shade, and has a decent foliage display in the autumn. As many introduced plants go, it went from prized ornamental to an unwanted “invasive species,” spreading across the landscape and affecting the environment. It is now widely recognized invasive species in many states or closely watched as a species likely to become invasive. That said, beyond the legacy of over half a century of mass plantings across the country, it is still common planted and old and new cultivars are commercially available.  USDA estimated over $23 million in sales in the US in 2009 alone.
 
How’d Callery pear get to the US? The story behind the introduction of Callery pear is a fascinating one.  Like many of our cultivated plants, seeds were collected on special expeditions in search of plants useful to horticulture, agriculture, or just because. Pyrus calleryana was first introduced to the US in the early 1900s, though not for its attractive blossoms as you might expect. Instead, it was first introduced for its disease resistance. It was successfully used in horticulture as a root stock for European pear fruit production. At the time, European pears in the Pacific northwestern US were being hit hard, grafting to a Callery pear rootstock dramatically decreased crop losses to disease. Callery pear does not produce edible fruit.

​The tree was widely planted starting in the 1960s, when it became commercially available and promoted by the nursery industry as a hardy ornamental tree.  Before that, it was planted by the US Department of Agriculture (USDA) for testing at Plant Introduction Stations in Corvallis, Oregon, and Glenn Dale, Maryland. One of these Maryland planted trees was targeted for its special traits and became the source of the hugely popular ‘Bradford’ cultivar (“Bradford pear”). In 1952, one tree was used to graft to rootstock, a plant propagation method making all plants genetically identical.  Other cultivars have since been commercialized, but ‘Bradford’ were/are exceptionally popular. Though intended to be sterile (non-reproducing), it turned out the trees were capable of setting viable seed.   The cultivars themselves are not invasive, but because multiple cultivars exist, together they can cross-pollinate to become invasive.

Herbarium specimens have been critical to understanding the spread of this species.  In a 2005 study, Dr. Michael Vincent (Miami University in Ohio) found that 50% all specimens examined over the range of 39 years were collected between 2000-2003.  Though some specimens  were collected in the 1960s in natural areas, it became widely “escaped” from cultivation in many natural  areas in the 1990s.
 
You may have noticed that most of our specimen images to date are those collected in Pennsylvania and surrounding states.  That’s because these specimens are being digitized as part of a multi-institutional project, the Mid-Atlantic Megalopolis Project, with the overarching goal to mobilize herbarium specimens across the region  to understand the effects of urbanization on plant life.  However, this project is a step towards digitizing the entire Carnegie Museum Herbarium.  The herbarium is worldwide in scope, and specimens in the Mid-Atlantic region accounting for only 35% of the 540,000 specimens.
 
As more specimens become digitized as part of the Mid-Atlantic Megalopolis Project, we’ll have a more complete understanding of the introduction and spread of Callery pear in the region.
 
Herbarium specimens are collected in the native range too! We’ll be able to compare specimens collected in the invaded range to those in its native China. The use of cultivated specimens and those collected in the native range are underutilized  but can provide critical information.

Escaped from cultivation. This specimen  (above) from Muhlenberg College Herbarium (MCA) was collected along the roadway in Montgomery county, Pennsylvania by Bayard Long in 1962. This specimen is probably the earliest specimen collected in the wild in Pennsylvania.

Many more specimens like this will be brought to light through the Mid-Atlantic Megalopolis Project.
 
Read more about this species introduction history in the popular press, published in the Washington Post  last year, and in an excellent overview by Dr. Theresa Culley (University of Cinncinati) in Arnoldia and another in BioScience.
 
See all the Pyrus calleryana specimens being made available online from the Mid-Atlantic Megalopolis project here: http://midatlanticherbaria.org/portal/collections/list.php?db=277%2C328%2C334%2C329%2C333%2C320%2C330%2C40%2C410%2C316%2C335%2C331%2C332%3B11&includecult=1&taxa=Pyrus+calleryana&usethes=1&taxontype=2
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​Many invasive species in our region were ironically first introduced intentionally.  The tree-of-heaven (Ailanthus altissima) is one such example, originally praised with enthusiasm as a lovely garden tree, fast growing, well behaved, resistant to pests and pollution – therefore an excellent urban street tree.  Tree-of-heaven was introduced first to Europe from northern China, then to North America in the 1780s to a garden in Philadelphia.  Decades later (and several additional introductions), it grew in popularity to become widely available and adopted for use in town and city plantings through the mid-1800s, including New York City.  By the 1900s, it was widely naturalized in both urban and rural areas across much of the United States.  It is now recognized by most states as an invasive species.  Tree-of-heaven was the namesake tree in Betty Smith’s 1943 classic novel, A Tree Grows in Brooklyn.
 
This specimen was collected by Sue Thompson and Lawrence LaSpoda on September 28, 1983 in Panther Hollow, not far from the Carnegie Museum in Pittsburgh.
 
Keep an eye out for this weedy tree, which is common throughout the city and along highways.  Its seeds are especially noticeably this time of year and persist on the tree into the winter.

​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.  

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.

Did you know Queen Anne’s lace is closely related to the carrot in your garden?  In fact, it is also called wild carrot. This specimen of Queen Anne’s lace aka wild carrot (Daucus carota) was collected in Coudersport, Pennsylvania (Potter county) on July 28, 1944 by Thomas K. Barrie.
 
Queen Anne’s lace is a common weed throughout the temperate world.  Its blooms are a sign of summer in Pittsburgh.  Not only is it in the carrot family (Apiaceae), but in fact, domesticated carrots are a cultivar of a subspecies of Queen Anne’s lace – Daucus carota subsp. sativus. 
 
Carefully pull this species out of the ground and you’ll find a hefty, fleshy tap root that looks and smells like the carrots we all know. 

Its white umbrella like clusters of flowers (called "umbels") are characteristic of the carrot family (Apiaceae), which also includes other well know species in our area such as poison hemlock.
 
Queen Anne’s lace is native to temperate Europe/Asia and was introduced to North America.  It is now widely naturalized in fields and roadsides.

Herbarium specimens can provide insight into plant-insect interactions.  For instance, many specimens show obvious signs of insect damage to the leaves or flowers.  Many other specimens, upon closer inspection under magnification, show damage that is much subtler.  Sometimes, even the larvae or insects were also pressed with the plant!  Some of this damage may have happened from pests in the herbarium that occurred over decades of storage.  Damage from herbarium pests is a serious concern and collection managers are also conservators of these archives, keeping a vigilant eye out for damage from the elements (such as light, temperature, humidity, water, and other chemicals) and introduced pests (such as mold and insects).  However, damage that occurs in the herbarium is minimized for long term preservation and luckily, insect damage that occurs in the herbarium is often easily distinguished from herbivory that happened in the wild, before the plant was collected, dried, pressed, and added to the collection.
 
Few studies to date have used the herbarium record to understand the ecology and evolution of plant-insect interactions. However, there are several pioneering studies at the frontier of this novel use of these collections.
 
This specimen pictured above of wild parsnip (Pastinaca sativa) was collected by Leroy Henry on July 17, 1968 along the Pennsylvania Turnpike not far from Pittsburgh.  Leroy Henry was an influential Curator of Botany at the Carnegie Museum from 1937-1973, having collected thousands of specimens in the herbarium.
 
In addition to the “standard” herbarium label that gives information on what the specimen was first identified as, where it was collected, who collected it, etc., check out another typed label affixed to this sheet.  This annotation label indicates two seeds were removed from for chemical analysis in 2005.  Annotation labels are commonly added to specimens years to centuries later to note its use in a study, a new identification, and/or part of the specimen was removed.
 

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This specimen was one of many specimens included in a study on wild parsnip by Zangerl and Berenbaum published in 2005 in the high-profile journal Proceedings of the National Academy of Sciences (PNAS).  
 
Wild parsnip (Pastinaca sativa) was introduced to the United States from Europe centuries ago and has since spread to become invasive.  The species is a member of the carrot family (Apiaceae).  Like many other species in this plant family, wild parsnip produce phototoxic chemicals called furanocoumarins, which protect the plant from insect herbivory.  These compounds also cause major skin irritations in humans, reacting with sunlight to cause nasty rashes.  This group of chemicals is of the same fame of giant hogweed, poison hemlock, and other well-known toxic plants in the United States.
 
Zangerl and Berenbaum (2005) analyzed herbarium specimens collected over the past 150+ years.  These specimens were collected from before wild parsnip was widespread in the US and compared those to specimens collected more recently, after the species was widely established.  A major herbivore, the parsnip webworm (Depressaria pastinacella) was also accidentally introduced in the mid-late 1800s.  The authors found that as rates of webworm attack increased, so did the toxicity of wild parsnip.  Specimens from 1850-1889 (early stages of introduction) had lower levels of the toxic furanocoumarins than plants collected more recently, as well as than specimens collected in their native range (Europe), where the parsnip webworm is also native.
 
There is so much known and unrealized potential in herbarium specimens.  This particular specimen was not collected with the intention of studying the ecology and evolution of plant-insect interactions.   This study helped inform our current and future use of biological control agents to manage introduced species.
 
These unanticipated uses (often decades to over a century after a specimen was collected!) illustrate the incredible power of natural history collections.
 
See an excellent paper by Meineke et al. just published on this topic (including quantifying the effects of climate change on plant herbivory through herbarium specimens): https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecm.1307.
 
Check out the cool parsnip webworm study here: http://www.pnas.org/content/102/43/15529

Wild parsnip (Pastinaca sativa) in an unmowed roadside median next to Bloomfield Bridge, Pittsburgh PA on June 29, 2018.

​​“This is, perhaps, the most execrable weed that has yet invaded the farms of our country.” 
William Darlington (1859) American Weeds and Useful plants, 2nd ed. 
 
This “execrable weed” described in the quote above by Darlington over 150 years ago was Canada thistle, Cirsium arvense (sunflower family; Asteraceae).
 
This particular specimen of Canada thistle was collected by Walter Zanol on July 14, 1990 near Tarentum, Pennsylvania (Allegheny county). 
 
Canada thistle is a common weed in agricultural fields, disturbed areas, and roadsides in Pennsylvania and across the world.  Although the common name suggests it is from Canada, this is misleading, as the species is from southeastern Europe and eastern Mediterranean.
 
It was among the earliest introduced plant species in North America by European colonists, with records suggesting as early as the 1600s.  It was probably introduced accidentally as a contaminant in crop seed.  It has since spread and become invasive in many US states and Canadian provinces. It remains a major agricultural pest today.
 
By 1851, it was already regarded a “most troublesome [sic] weed, which is extremely difficult to eradicate” in Pennsylvania (Knoll, 1851).
 
It is a weed of many major crops, causing economic harm through reduction of crop yields.  It spreads both sexually (through seeds) and asexually (through underground rhizomes).  It is not uncommon to see many individuals of this species forming dense patches in fields or along the road.  These patches are likely connected belowground (or once were connected).  Because of this attribute of spreading via creeping lateral roots, it is also known as “creeping thistle.”
 
Its purple flowers and spiny stems/leaves are similar at first glance to many thistles, but its horizontal, creeping lateral roots make this species easily distinguishable from the many other non-native and native thistles in Pennsylvania.
 
Keep an eye out for this species.  It can be spotted throughout Pennsylvania this time of year, often forming dense stands that are going to seed.  Their seeds go airborne, looking almost like snow or cotton flying through the air.

 

​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. 

Spring leaf out is a bit “behind” in Pittsburgh this year.  Well, for Norway maple in Schenley Park compared to 1948.  Plant leaf out and flowering times is variable for many species each year due to differences in spring temperatures. This Norway maple specimen was collected by Botany curator Otto Jennings.  Norway maple (Acer platanoides) is commonly planted across our region, common as a street tree or park plantings.  Norway maple is invasive in Pennsylvania, spreading into natural habitats. Its leaves superficially resemble the well known sugar maple but has a different leaf shape. Norway maple has even been put on the Canadian 20 dollar bill instead of the native sugar maple (http://www.cbc.ca/news/canada/ottawa/canada-s-new-20-bill-at-centre-of-maple-leaf-flap-1.1343767). A good way to tell it is Norway maple is that exudes a white latex from the leaf when picked.

Keep an eye out for Norway maple over the next week!  That light yellow/green you see at the tips of trees (especially along highways) in early spring is not tree leaves, but flowers. And many of these trees in urban areas around Pittsburgh are Norway maple.  Many trees flower early in the spring, before they leaf out.  Many tree species are primarily wind pollinated, so flowering before most species leaf out facilitates pollen to blow around with fewer obstructions.
 
In a long-term project initiated last year, we are recollecting specimens on the same calendar date and in the same location as historic specimens in the herbarium.  These recollections will grow the herbarium with future use in mind – permitting comparisons across time, such as changes in leaf out dates, flowering, and genetic works.  Long term studies (and herbarium specimens) are important to understand the effects of climate change and other human activities because of yearly variation.  Check back for more on this project!
 
Image below: Norway maple buds today on a tree in Schenley Park, Pittsburgh (Apr 4, 2018).  It is not quite ready to go. Note the buds are swollen but are not yet burst.  Compare this to the specimen collected in 1948, in full flower and early stages of leaf expansion.

​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.