HEBERLING LAB

 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.

There’s a deeper evolutionary history behind jack-o-lanterns and pumpkin spice lattes than you might think.  Recent research from Penn State indicates the plant lineage might have went extinct had it not been for humans.  Species in the genus Cucurbita (including pumpkins, gourds, squashes) were domesticated by humans in eastern North America about 10,000 years ago.  That is, they were cultivated in gardens, likely first selected for the use of their durable rinds (anthropological evidence for gourds used as containers for drinking) and later as a food source.  Most Cucurbita species went extinct around this time, coinciding with the extinction of large mammals that these species relied upon to spread their seeds.  Their fruits were unpalatable to the smaller herbivores that did not go extinct. Ironically, it is human hunters, paired with climate change, that led to the extinction of large herbivores in North America.  Modern day pumpkins have adapted to the Anthropocene.

​Collected near Freedom (Beaver county, PA), this pumpkin specimen (Cucurbita pepo) was collected from Dun’s Farm in 1884 by John A. Shafer, who became the first Curator of Botany at the Carnegie Museum of Natural History a decade later.

Collected in 1908 (the first year Mother’s Day was celebrated!), this specimen was grown in cultivation at the former western headquarters for the Ferry-Morse Seed Company in Mountain View, California.  The white carnation was chosen as a Mother’s Day symbol by Anna Jarvis, the holiday’s founder, because they were her mother’s favorite.  Carnations remain closely associated with Mother’s Day in the United States, with white carnations traditionally as symbols in memory of mothers who have died and colored carnations to honor living mothers. The carnation, or Dianthus caryophyllus, is probably native to the Mediterranean, but its native range is obscured by at least 2,000 years of cultivation.  There are over 27,000 named cultivars of Dianthus species.

Collected in Ireland in 1891, this specimen (above) was found by Susan and Edward Harper, who were plant collectors from the Field Museum in Chicago.  This specimen is a clover species (Trifolium campestre), known as hop trefoil or field clover.  Clovers are a group of species that usually refers to those belonging to the genus Trifolium, meaning “three-leafed.”  For next year’s post, I'll look for that mystical 4-leaf clover among the 1,877 clover specimens in the Carnegie Museum’s Herbarium.

So what exactly is a shamrock? There is no overwhelming scientific consensus on which species is the well-known Irish national emblem.  There was survey of Irish botanists in the early 1890s asking which species was the “true” shamrock.  A similar survey was repeated in 1988.  The results suggest the shamrock is either Trifolium dubium (aka “lesser trefoil”) or Trifolium repens (aka “white clover”).  But there are no official rules for common names.  The plants commonly sold around St. Patrick’s Day as “shamrocks” or “4-leaf clovers” are in the plant genus Oxalis (“wood sorrel”), which belong to different plant family than true clovers.
 
Top left: Trifolium repens (collected 1974 in Louisiana), “white clover” likely seen in your backyard
Top right: Trifolium  dubium (collected 1961 in Pennsylvania), aka “lesser trefoil”
Bottom left: Oxalis tetraphylla (collected 1981 in India), aka “lucky clover,” although not a true clover
Bottom right: Oxalis debilis (collected 1989 in cultivation), aka “pink woodsorrel”

Collected on February 14, 2005, this specimen was found in Costa Rica by John Paul as part of his graduate research at the University of Pittsburgh.

This species is particularly appropriate for Valentine’s Day because before it flowers, it produces deep red, petal-like leaves called bracts that resemble human lips. Psychotria elata (also known as  “hot lips” or "hooker's lips") is part of an important group of plants in the coffee family, native to tropical forests across the world.