Mason Heberling

What are those yellow flowers?
A common roadside plant.
 
This specimen of yellow rocketcress (Barbarea vulgaris) was collected in Lower Burrell, Pennsylvania on May 28, 1993 by Fred Utech.  Utech (1943-2021) was a curator at the museum from 1976 until 1999.  More than 23 thousand specimens in the Carnegie Museum herbarium were collected by him.
 
Yellow rocketcress (or simply “yellow rocket” among many other common names) is a plant in the mustard family (Brassicaceae) with yellow flowers that bloom in mid to late spring.  Introduced from Europe/Asia/North Africa, it is now very common in Pennsylvania and many parts of North America. It is a common site along roads, especially ditches along highways.
 
Find this specimen (and 474 more!) of yellow rocket here: https://midatlanticherbaria.org/portal/collections/list.php?db=328&taxa=Barbarea+vulgaris&usethes=1&taxontype=2
 

Collected on June 2, 1994, this specimen was found along Neshannock Creek in Mercer County, PA by Bonnie and Joe Isaac.  Bonnie is the collection manager in Botany at the museum.  She and her husband, Joe, are both professional botanists and active collectors.  Over 20,000 specimens in the Carnegie Museum herbarium have been collected by them.
 
Garlic mustard (Alliaria petiolata) is a non-native species from Europe that invades roadsides and forest understories across the eastern US, often displacing native species.  Garlic mustard has also been shown to produce chemicals that inhibit the growth of fungi in the soil that form a symbiotic relationship with the roots of many native forest species.  It has also been shown to be facilitated by overabundant deer.  Garlic mustard was introduced from Europe and first reported in Long Island in 1868.  However, it was not widely recognized as a widespread invasive species until the early 1980s. Scientists are using herbarium specimens to study the introduction and map the spread of this invasive species through time.

Collected on June 3, 1937 by J. Churchill in a vacant lot in Mt. Lebanon, this specimen is the oldest garlic mustard voucher for Allegheny county, Pennsylvania.  Introduced to the U.S. in the late 1860s, garlic mustard (Alliaria petiolata) was a kitchen herb, but escaped gardens and is now a problematic weed in forests and roadsides across the eastern US.

Collected on April 28, 1845, this specimen was found in Mercersburg, PA (Franklin County) by Thomas Conrad Porter.  Porter (1822-1901) was a botanist associated with the herbarium at what is now the Academy of Natural Sciences of Drexel University in Philadelphia.
 
This puny plant might not seem like anything to write home about, but is well known by most scientists.  Arabidopsis thaliana (mouse-ear cress) has played and continues to play a huge role in plant biology research.  This weed in the mustard family (Brassicaceae) is native to Europe and Asia and widely introduced to the US.  Because of its small genome (fully sequenced 16 years ago), rapid life cycle (germination to reproducing adult takes only 6 weeks!), mutant genotypes, and a long history of genetic research, this species has become an important model organism for cellular, molecular, evolutionary, agricultural and even ecological studies. It is the international “lab rat” for plant science.  It was discovered in Germany in the 1500s, but did not really become famous as a model organism for research until 1943 – nearly 100 years after this specimen was collected!