HEBERLING LAB

​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. 

Collected on August 8, 1901, this American chestnut (Castanea dentata) specimen was found near Blairsville, PA by John Shafer (Carnegie Museum's first botany curator).  America chestnut was once a major player in eastern US forests, especially Pennsylvania and the Appalachian Mountains.  American chestnut provided many ecological functions, including an important food source for wildlife and was prized by humans for its wood. Some estimated that one in four trees in some forests were American chestnut. But no longer due to chestnut blight, a disease caused by a pathogenic fungus (Cryphonectria parasitica) introduced in the early 1900s from Japan. The species went from an important component of many forests to being functionally extinct.  The species can still be found in some places as resprouted shoots from existing stumps, but they do not reach reproductive maturity.  Breeding efforts are underway to restore the American chestnut through creating blight resistant chestnuts by cross-breeding with Chinese chestnuts, which are blight resistant.  There are 264 American chestnut specimens in the Carnegie Museum’s herbarium, which document the distribution and biology of this important species before and after the blight.  This specimen picture here was collected before chestnut blight was known in the US.