Mason Heberling

 What you know as yams are most likely not really yams.  In fact, your “classic” potatoes, sweet potatoes, and yams are all in different plant families. However, they all are widely cultivated for their nutritious starchy belowground plant structures called “tubers.” Tubers function as storage organs for the plants, providing energy for regrowth (the “eyes” or sprouting buds of your potatoes when they sit in your kitchen for too long).  Potatoes and yams technically have modified belowground stems (“stem tubers”) while sweet potatoes have “root tubers.”
 
Yam is a common name for several vine species in the genus Dioscorea (plant family: Dioscoreaceae).  They are monocots (related to grasses and lilies). Yams are widely cultivated worldwide, especially in West Africa, where 95% of the crop is harvested.  Yams can be stored for very long periods of time, making them an important crop for seasons when food is in short supply.  Yam tubers can be as large as five feet long!
 
Sweet potatoes refer to a vine species (Ipomoea batatas) in the morning glory family (Convolvulaceae).  This species is likely what is on your Thanksgiving dinner table.  In the United States and Canada, sweet potatoes are often (confusingly) referred to as “yams.”  But sweet potatoes are not even closely related to yams.  As such, the USDA requires any label with “yam” to also include “sweet potato.”  So why are sweet potatoes sometimes confusingly called yams?!  Well, this naming probably dates back to colonial times when slaves from Africa noted the similarities between some varieties of sweet potatoes to yams in Africa.
 
 And last - the “classic” potato, Solanum tuberosum.  Potatoes belong to the nightshade family (Solanaceace), which also includes many other important crops like peppers, tomatoes, tomatillos, eggplant, tobacco, and more.  Critical to the world’s food supply, potatoes are the fourth most farmed crop.  Potatoes are only distantly related to sweet potatoes.  They are also called “spuds,” which probably originated centuries ago from a term for a spade used to dig holes to plant potatoes. Having been cultivated for centuries, there are thousands of potato varieties worldwide.  The cultivated species was domesticated from wild relative potato species in South America (Peru) 7,000 – 10,000 years ago.  Important discoveries on the origin of potatoes were based on DNA from 200 year old herbarium specimens!  Similarly, the origin of the Irish Potato Famine (caused by potato late blight from a fungal pathogen) was also discovered using fungal DNA extracted from 160+ year old herbarium specimens! 
 
For more on cool new Irish potato famine research:  http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168381
 
For more on origins of European potato: https://www.ncbi.nlm.nih.gov/pubmed/21632349
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Specimen above: "Yam" species (Dioscorea schimperiana) collected in 1960 by A.C. Twomey in Kenya.  Yams are an important food crop across Africa.

Specimen below: "Sweet potato" (Ipomoea batatas 'Georgia Jet') collected in 2001 by Bonnie and Joe Isaac in a garden in Pennsylvania.

Specimen below:  Your "classic" potato (Solanum tuberosum) collected in 1982 from a farm in Peru.  Research suggests Peru to be the site of early domestication over 7,000 years ago.

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.

This isn’t your typical herbarium specimen of Sassafras (Sassafras albidum). On November 4, 1933, this piece of Sassafras wood was collected by Otto Jennings at Linn Run/Rock Run, about 5 miles south of Ligonier, PA.  It is unclear what motivated this collection, since Jennings did not normally collect wood like this.  Given its bulky size, it is stored with the fruit collection in the herbarium, separate from the typical pressed specimens. 
 
Sassafras is a medium-sized deciduous tree, native across Eastern North America. It is easily recognized by its uniquely mitten shaped leaves.  The leaves are very aromatic when crushed in your hand, like many other species in the Laurel family (Lauraceae).  They also turn a beautiful red in fall.
 
Sassafras has long been used by humans for medicine and food, both by Native Americans and later Europeans.  Ever wonder where the “root” in root beer comes from?  Root beer was traditionally made from sassafras roots or bark.  But, since 1960, sassafras is no longer used in commercially made root beers. The FDA has shown safrole (the aromatic oil in sassafras roots and bark) to cause liver damage and/or cancer in high doses to laboratory animals.  Many commercial root beers nowadays use artificial flavors.

Above: Specimen showing leaf shapes of Sassafras, collected by Hanne F. von Fuehrer,.  She was instrumental in preparing many of the plants in Botany Hall at the Carnegie Museum of Natural History.  Her work was often based on museum specimens.
Below: Sassafras in Fall.