HEBERLING LAB

Some dogwoods for the dog days of summer
 
Who doesn’t love a good dogwood? Perhaps you are most familiar with flowering dogwood (Cornus florida), with the beautiful showy white flowers in woods and wooded roadsides across Pennsylvania in the spring.  Or perhaps, the commonly planted Japanese dogwood (Cornus kousa) from...you guessed it...East Asia.  But there are many different dogwood species, all in the genus Cornus.  Species in the genus are distributed across much of the temperate world in the Northern Hemisphere.  Rhoads & Block Plants of Pennsylvania list nine species found in the wild in our state.  They are trees or shrubs (with one exception). The veins on their leaves are quite distinctive, as is their bark and flower structures.
 
Why are these shrubs called dogwood?  There are several stories behind the unique common name. One is that the name was derived from the Celtic word “dag”, referring to its use of its nice wood as a dagger like tools or skewers. Another explanation is that the bard was once used as a treatment of mange for dogs.
 
Four dogwood species were collected on June 28 in Pennsylvania: 69,  37,  26, and 23  years ago:
 
Red-osier dogwood, Cornus sericea (aka Cornus stolonifera) June 28, 1950 in Erie County. Beautiful bright red stems.
 
Gray dogwood, Cornus racemosa June 28, 1982 in Blair County.
 
Cornus ammonum June 28, 1993 in Clarion County.
 
Cornus florida June 28, 1996.  White flowers from the spring are long gone.  (Well, the white structures aren’t actually petals, but modified leaves called bracts that surround a cluster of small yellowish flowers).
 
Over 2,600 dogwood (Cornus) specimens in the Carnegie Museum herbarium from across the world are available online, many with high resolution images: http://midatlanticherbaria.org/portal/collections/list.php?db=328&taxa=cornus&usethes=1&taxontype=2

Whoa, this plant will catch your attention!  Although towering in at up to 8 feet tall with leaves 2 feet wide, Cow parsnip (Heracleum maximum, aka Heracleum lanatum) is not a tree, but herbaceous (non-woody). This species is the largest member of the carrot family (Apiaceae) native to North America. It can be found along shaded roadsides, waterways, and edge of woods. Its flower structure consists of many small white flowers on short stalks connected at a single point – an umbrella of flowers - botanically known as an “umbel.” Umbels are characteristic of the carrot family (think of the perhaps better recognized Queen Anne’s lace, Daucus carota, which is also known as “wild carrot”).
 
These specimens were all collected on June 21– but years apart - on 1907 (Westmoreland county, PA), 1934 (Pittsburgh), and 1960 (Beaver county, PA).   
 
This species is often confused with giant hogweed. Cow parsnip is often confused for the non-native plant called giant hogweed (Heracleum mantegazzianum). Giant hogweed has hit the news media in past few years and on many people’s radar, as it is considered a significant public human health concern. This plant is highly poisonous and designated as a federal noxious weed.  The sap of giant hogweed causes “phytophotodermatitis,” meaning serious skin inflammation occurs when contacted skin is exposed to sunlight.  Skin rashes can be very severe.  The sap can cause temporary or permanent blindness. Cow parsnip has a similar set of chemicals in its sap, and although not as poisonous, be  careful around these plants.
 
Giant hogweed can be 8-20 feet tall with leaves up to 5 feet wide!  It is thought to be eradicated in Pennsylvania. Although similar to the Pennsylvania native species cow parsnip, giant hogweed is noticeably larger in height and flower size. (see herbarium specimen here – it took 6 sheets!)
 
See here for a nice comparison between these similar species. https://www.maine.gov/dacf/php/horticulture/hogweedlookalikes.shtml
 
Given the size of members of the genus, the name Heracleum (derivative of Hercules) is quite fitting.
 
Specimen records and images for this species in the CM herbarium are now publicly available online:
http://midatlanticherbaria.org/portal/collections/list.php?db=328&taxa=Heracleum+lanatum&usethes=1&taxontype=2

Not all bittersweet vines are invasive to Pennsylvania. This specimen was collected on June 14, 1965 by botany curator Leroy  Henry  in Clearfield county,  along  Rt 969. American bittersweet (Celastrus scandens) is a woody vine that  blooms in June, which turn to beautiful clusters of orange/red fruit in late summer/fall.  The species is native to eastern USA, found along open thickets/edge of woods.

American bittersweet (Celastrus scandens) might be easily  confused with the much more common Asian bittersweet (Celastrus orbiculatus).  There are two major visual  differences between the species: 1) flower/fruit --  native species has single terminal cluster of many flowers/fruits at tips of branches, whereas the invasive has flowers/fruits at axils of leaves (where leaves connect to stem; and 2) leaves -- native  species' leaves are more elongate, whereas the invasive species' leaves are more round, often even circular ('orbiculate').

American  bittersweet is no longer common in Pennsylvania, most likely taken over by the closely  related Asian bittersweet.   Asian bittersweet  is a relatively newer addition to the  flora of Pennsylvania, not showing  up  in  western PA and  the  Pittsburgh region until  the 1980s.  Given its abundance and distribution throughout the region  now,  it is hard to fathom it was not present only several decades ago.

Research over the past decade has shown that the invasive species hybridizes with the native, likely contributing to  the decline  of the native American bittersweet.

Keep a look out for American bittersweet in our region.  (I have  not  seen it in Allegheny county, although we have historic  records)

This specimen image is now publicly available online:
http://midatlanticherbaria.org/portal/collections/individual/index.php?occid=12131436&clid=0

This is a special specimen.  The Carnegie Museum herbarium is full of specimens of scientific and historical importance.  And this is a notable one, collected in June 1830 by William Darlington in West Chester, Pennsylvania.  William Darlington (1782-1863) was an important figure in the history of Pennsylvania botany. Darlington was a physician, politician (US House of Representatives 1815-1823),  and as  you might guess – a botanist!  At the University of Pennsylvania, Darlington studied botany under Benjamin Smith Barton, a well-known botanist who also trained Meriwether Lewis (of the Lewis & Clark Expedition). Darlington wrote several He spent most of his life in West Chester, PA. He wrote some of the earliest botanical works, including a flora of Chester County in 1826 and others on agriculture.  Many of his specimens are among the earliest documentation of Pennsylvania’s flora and are preserved in the William Darlington herbarium at West Chester University.
 
This particular specimen is of the native shrub Euonymus americanus, commonly called “strawberry  bush.”  Despite the name, it is not related to strawberries, but in the bittersweet/spindle family, Celastraceae.  You may recognize some similarities with the related species from East Asia, burning bush  (Euonymus alatus), which is commonly planted for its bright red fall color (around Cathedral of Learning in Pittsburgh, and many other places).  However, burning bush should not be planted, as it is invasive, spreading into natural areas.
 
In the Carnegie Museum herbarium, there are 62 specimens collected by Darlington between 1828 and 1840, mostly from Chester County, PA. 
 
How’d some of Darlington’s specimens end up at the Carnegie Museum?  This specimen was part of Jacob Wolle’s personal collection, who was the grandfather of William Holland, the first director of the museum.
 
This specimen image is now publicly available online: http://midatlanticherbaria.org/portal/collections/individual/index.php?occid=12131484&clid=0
 
Read more about  Darlington and other influential figures in the history of Pennsylvania botany at Herbarium World: https://herbariumworld.wordpress.com/2017/07/10/william-darlington-and-the-pennsylvanica-botanical-circle/