HEBERLING LAB

Why do some deciduous species still have leaves in the winter?  This specimen of American beech (Fagus grandifolia) was collected by Bayard Long in Philadelphia 67 years ago.  Surprised to see leaves in February?  Signaled by shortening days, most deciduous trees in our region drop their leaves in the fall when a layer of cells form at the base of the leaf, forming an “abscission zone.”  This abscission zone is formed by weakening cell walls, thereby separating the leaf from the stem.  However, this doesn’t happen in all deciduous plants.  The retention of these leaves is called “marcescence.”
 
In our area, some species keep their dead leaves through the winter, and it can be quite beautiful on a snowy day.  In particular, beech and oak species retain their dead, brown leaves through the winter, especially on lower branches and in small plants. Why?  Well, I’m not convinced we really know.  There are a few reasons that have been suggested.   
 
Some of these ideas include:
1) serves no adaptive function, but just a byproduct of evolution,
2) deters animals (like deer) from eating stems in the winter,
3) facilitates better nutrient absorption and/or ensures leaf litter mulch layer in the spring when the leaves fall to ground (leaves decays faster once on the ground),
4) protect the leaf buds for next year from drying out or frost damage in the winter. 
 
I’m sure there are other hypotheses too.  Species differ in their leaf out times, leaf drop times, leaf lifespans.  The who, what, when, where, and why of evergreen and deciduous leafing strategies is fascinating.  And much remains unknown.
 

The persisting, dead leaves that remain on American beech can make for quite a scene in the winter. 

Specimen with no leaves! These twigs of white ash (Fraxinus americana) were collected in 1926 by J.K. Doutt along Squaw Run, PA.  Many specimens in the herbarium were collected from Squaw Run, especially in the late 1800s/early 1900s. Squaw Run is a tributary of the Allegheny River, that runs through Fox Chapel and O'hara Townships. Specimens without leaves are not common, and it is unclear what the exact motivations behind this collection was.

White ash (Fraxinus americana) is a common tree in forests across the Eastern US.  They are currently threatened by the Emerald Ash Borer (Agrilus planipennis), an invasive beetle that was accidentally introduced from Asia.  It was only detected in North America in 2002, and not in Pennsylvania until 2007!  It has the potential to cause our native ash trees (all native species in the genus Fraxinus) to extinction, rivaling the impacts of the Chestnut Blight on American chestnuts in the early 1900s.

​Does this heart-shaped leaf look familiar?  22 years ago, this specimen of heartleaf philodendron (Philodendron hederaceum) was collected on Valentine’s Day in Peru.  Almost certainly you have seen this species, but probably not in the wild.  Heart leaf philodendron is a very popular houseplant. This huge leaf on this specimen may look a bit different than those in your home, as the species rarely reaches maturity as a houseplant.  Philodendrons have both juvenile and adult forms of their leaves, changing their form and size as they climb up a tree.   
 
The name Philodendron comes from the Greek philo meaning “love” and dendron meaning “tree.”  The name doesn’t refer to the heart shaped leaves, but rather to its growth habit as a vine that climbs trees.  It is native to tropical Mexico, the Caribbean, and regions in South America.
 
Happy Valentine’s Day from this loving plant!

In honor of the cool, new Tropical Forest Cuba that opened yesterday at Phipps Conservatory and Botanical Gardens, here’s a specimen collected in Cuba 115 years ago today.  This pine specimen of Pinus elliottii, known as slash pine or Cuban pine, was collected by George Russell Shaw in the Isles of Pines, Cuba (now known as Isla de la Juventud).  Shaw was an influential botanist working at the Arnold Arboretum (Harvard) who specialized in pines.   
 
The Carnegie Museum of Natural History has many specimens from Cuba.  Curator of Botany Otto Jennings and others went on expeditions to Cuba in the early 1900s, and many specimens are now preserved at the Carnegie Museum and elsewhere.  The Carnegie Museum herbarium includes 4,068 specimens from Cuba, of which 54 are type specimens (meaning they are associated with the description of a species new to science). 
 
Learn more about the plants and culture of Cuba at Tropical Forest Cuba at Phipps Conservatory and Botanical Gardens!

Above: Publication resulting from expeditions to the Isles of Pines, written by one the first curators of botany Otto Jennings, who researched the plants of Cuba. 631 specimens from Cuba collected by Jennings reside in the Carnegie Museum herbarium today. 

​Don’t grab on to this tree to catch your fall!  Aptly named “devil’s walking stick,” this species (Aralia spinosa) was collected on February 9, 1935 by John F. Lewis near Connellsville, PA.  The herbarium at the California University of Pennsylvania is named after John Lewis.  Many of his specimens in the herbarium are twigs collected in winter, without any leaves. 
 
Devil’s walking stick, also called “Hercules’ club” is a small shrub/tree native to forest understories, ravines, and forest edges across the Eastern United States.  It has huge leaves comprised of many leaflets, and as can be seen from this specimen – impressive, sharp spines along the stem (technically called “prickles” in botanical speak).  The prickles are so large that the specimen was too thick to image with our scanner used for other specimens.
 
This plant is often grown in cultivation due to its unique look, as is the closely related (and very similarly looking) Japanese angelica-tree (Aralia elata), which is native to East Asia. Japanese angelica-tree is listed as an invasive species under the highest rank (“Severe Threat”) by the Pennsylvania Department of Conservation and Natural Resources due to its ability to spread into wild habitats and displace native plants.

Above: Uniquely huge compound leaves and fierce stems of Devil’s walking stick in a forest near Salisbury, PA (Somerset county; May 8, 2017).

Below: Striking similarities to the closely related East Asian species Aralia elata.  (Mt. Pidan, Russian Far East; September 30, 2012).

Collected on February 2, 1899, this specimen was found by Cyrus Pringle in lava fields near Cuernavaca, Mexico.  Pringle is a well-known American botanist and prolific plant collector, with over 500,000 specimens distributed in herbaria across the world!  To give this enormous number some context, his collections alone are nearly the size of the entire Carnegie Museum herbarium.  The herbarium at the University of Vermont is named after him.  The Carnegie Museum herbarium includes 5,378 specimens he collected.  During his life (1838-1911), Pringle discovered approximately 1,200 new species. 
 
In addition to the Northeastern US, many of Pringle’s specimens are from Mexico.  In 1885, Pringle was funded by Harvard to document the flora of Mexico.
 
This particular specimen is a type specimen of Agave hispida, meaning this particular specimen was used in the naming and description of this species as new to science.  There are many different categories of type specimens. More specifically, this specimen is considered an isoneotype: “iso-“ because it is a duplicate of the “neotype” (collected from the same plant).  The “neotype” is “neo-” (or new) because it was designated as the type after the original publication that first described the species.  The neotype of this species (pictured below) is in the United States National Herbarium (Smithsonian).