Mason Heberling

Redbud is sure to catch your eye in the spring!  The picture above of redbud (Cercis canadensis)  in bloom was taken yesterday at Schenley Park.  Below illustrates how advanced leaf out was last spring (specimen on right), compared to 1915 (specimen on left: flowers, no leaves yet).  

Kudzu is one of the more well-known weeds, at least by name, sometimes known as “the vine that ate the South.”  Collected on October 13, 1997, this specimen was found by Sue Thompson and Bonnie Isaac near the I-376 Squirrel Hill tunnel, Pittsburgh. Kudzu (Pueraria lobata) was introduced to the US as an ornamental in 1876 at the Centennial International Exhibition in Philadelphia.  The vine was initially prized in the South to provide shade.  The vine was later promoted for use in erosion control.  Although listed as a noxious weed in PA, it is more invasive in southern states.  There, it has been estimated to spread at a rate of 2,500 acres per year (some say up to 150,000 acres per year, although this estimate has been questioned).  Infestations of this plant undoubtedly causes ecological and economic damage.
 
Below is another specimen of kudzu, collected in its native range in Japan in 2002.  Although plants are collected in both native and invasive ranges, few studies have compared specimens of the invasive species across continents.

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”