Mason Heberling

​​“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.

 

Plants are an important part of the urban landscape – both those planted species and those that are wild. There are more to “weeds” than you might think.  From sidewalk cracks downtown to city parks, plants are important to the ecological, economic, and human health of our city.  Understanding what plants thrive (or not) and their roles in a healthy, functional ecosystem in cities and human dominated environments that define the Anthropocene. With a recent award from the National Science Foundation (starting this September and running for 3 years ), we will be digitizing all specimens in the Carnegie Museum’s herbarium from the Mid-Atlantic Region (PA, MD, NY, NJ, DE & Washington, DC).  That is a total of nearly 190,000 specimens!  We are partnering with an ongoing herbarium digitization initiative, the Mid-Atlantic Megalopolis Project, which includes 11 other institutions in an effort to document and understand the past, present, and future plants in urban environments.
 
This specimen of Bellis perennis, also called “lawn daisy,” was collected just outside the museum in front of the Carnegie Library by former botany curator Otto Jennings on May 26, 1909.  This member of the sunflower family (Asteraceae) is native to Europe but has since been transported across the world and has become naturalized in many areas, joining the urban flora.
 
This project will facilitate a better understanding of the often-overlooked biodiversity in the city and the plants that make up Pittsburgh, both today and 150+ years ago.
 
Expect more posts in the coming months that highlight the Plants of Pittsburgh!  

​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.

​Nancy Hanks Lincoln (mother of Abraham Lincoln) died on Oct. 5, 1818 from “milk sickness.”  Milk sickness is caused by poisoning after drinking milk from cows that have eaten the plant white snakeroot (Ageratina altissima).  Also known as “puking fever” or simply “the trembles,” early European-American settlers in the Midwest initially thought milk sickness was an infectious disease.  It was soon realized that the unidentified illnesses were caused by drinking milk from cows that ate white snakeroot, which contains the chemical tremetol, a toxin which causes weakness, pain, vomiting, abdominal pain, and can lead to coma and death.  The cattle of these early settlers often wandered into the forest to graze, seeking additional forage outside limited pastures.  However, milk sickness is very uncommon today due to modern farming practices and cows rarely have access to eat this plant.
 
White snakeroot is a fall blooming, shade-tolerant species found in forests across the Eastern US, and commonly found throughout southwestern PA.  This specimen pictured was collected in 1998 in southwestern Indiana, about 90 miles north of the Little Pigeon Creek Community, where Abraham Lincoln’s family lived.

Another fall blooming aster!  ​Collected on October 6, 1896 (same year Carnegie Museum was founded!), this specimen was found by early museum botanist John Shafer on Jack’s Island, a small island on the Allegheny River (between Harrison Twp and city of Lower Burrell).   Despite the name, New England aster can be found across eastern North America.  Along with many other species in the genus Aster, this species was recently reclassified in the Symphyotrichum genus.  Symphyotrichum novae-angliae is a perennial (lives for several years) with beautiful deep blue-purple flowers.  Like other plants in the sunflower family (Asteraceae), the “flowers” are actually a cluster of flowers (heads) composed of many flowers, with “ray” and/or “disk” flowers.  

North America used to have over 150 species in the genus, Aster.  But now only one species remains.  That isn’t because they went extinct, but instead, they were re-named.  Many of these species are still referred in general as “asters.”  Collected on September 22, 1900, this specimen was found in Fern Hollow, Frick Park, Pittsburgh by early museum botanist John Shafer. Eurybia divaricata (formerly Aster divaricatus) is commonly known as “white wood aster.”  This beautiful fall blooming plant (like many asters) is a common native in eastern US forests.  So why the new name?  Taxonomy (the science of classifying organisms) is an ever-changing science, subject to revision as more research is done, especially at the molecular (DNA) level.  As we understand how organisms are related, we can better understand the history of life on earth.  Taxonomic studies of plants often lead to splitting of one species into many or the lumping of many species into one. In some cases, a “new” rare species may be have been hiding under our noses, previously grouped with another species. These studies are important for the conservation and protection of vulnerable species. We must know what these species are to actually protect them!
 
Like most herbaria (plural for herbarium), the Carnegie Museum herbarium is organized by genus within families.  Earlier this year, collections manager Bonnie Isaac and a team of interns and volunteers reorganized the sunflower family (Asteraceae), one of the largest families of flowering plants.  After a month of reorganizing and renaming folders, the work is still ongoing.  No surprise, as this family is represented by over 51,000 specimens (or about 10% of the entire collection)!  Ongoing taxonomic rearrangements like these are just one reason why the work of herbarium staff is never done.

​It is that time of year when old fields across western PA are painted yellow.  Collected on September 15, 1946, this specimen was found in New Baltimore, Somerset county, PA by an influential Curator of Botany at the museum, Otto Jennings. There are many species of goldenrod (in the genus Solidago) in our region.  They are often associated with runny noses and sneezing from fall allergies (hay fever), but don’t blame the goldenrods! Their relatively heavy pollen rarely becomes air-borne, but rather these plants are insect-pollinated.  Wind-pollinated species, like ragweed, are more likely your culprit.
 
This specimen pictured here (split between two herbarium sheets) is Canada goldenrod (Solidago canadensis).  Canada goldenrod is a fall blooming native species common throughout western PA.  However, it was introduced to Europe and Asia for use in floral arrangements and gardens, and has since become an invasive weed in other parts of the world.

​Collected on September 1, 2005, this specimen was found in a floodplain forest near the Monongahela River in New Eagle, PA (Washington county).  Ironweed (which includes many species in the genus Vernonia) is a great plant for native pollinators.  Consider adding it to your garden!  This species of ironweed, known as “tall ironweed” (Vernonia gigantea), can be 2-7 feet tall (or sometimes more than 10 feet!) with beautiful purple flower heads from mid-late summer.  Learn more about ironweed (and see it all year long) in Botany Hall at the Carnegie Museum of Natural History.

​Collected on August 26, 1998, this specimen was found along a gravel road not far from Settlers Cabin County Park.  Ragweed is a plant many people are (all too) familiar with.  Or at least their bodies are.  Common ragweed (Ambrosia artemisiifolia) is native to North America, but has been introduced across the world.  In many cases, this plant (or other ragweed species) are to blame for seasonal pollen allergies known as “hay fever.”  In summer and early fall, ragweed plants produce copious numbers of pollen grains, which are dispersed in the wind.
 
Although ragweed is native in the US, historical records (pollen deposited in sediment cores) suggest that this species was far less common in North America before European colonization.  This is perhaps not too surprising considering the species thrives in disturbed habitats that came with European colonization and urbanization.  A study published in 2014 by Martin and colleagues in the journal Molecular Ecology extracted DNA from nearly 500 historic herbarium specimens dating back to the 1800s to measure the genetic makeup prior widespread changes to the landscape in the late 19th century. Combined with data from recent collections, they found shifts in the genetic makeup of ragweed populations as the species was expanding in the United States.  

​Collected on August 18, 1941, this specimen was found just outside of Philipsburg, PA (Centre county) by Leroy Henry.  Bull thistle (Cirsium vulgare) is a European plant introduced in PA, commonly found in disturbed sites, roadsides, and fields.  As the species is unpalatable to most grazing livestock, bull thistle is often in abundance in grazed fields.  It is not uncommon to find American goldfinch pecking at thistle flowerheads, eating the seeds. Recognizable by their spiny stems and flowers (usually purple), thistles are in the sunflower family (Asteraceae), many of which are native to the US.