HEBERLING LAB

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.

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​)!

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.