Mason Heberling

​We don’t always think of trees when we think spring wildflowers. But trees can have flowers too.  Many trees flower in early spring, before leafing out. Many of these flowers are small and inconspicuous, and wind pollinated. This specimen of sugar maple (Acer saccharum) was collected in April 1898 in Olena, Ohio. This specimen was collected by Otto Jennings, one of the first botany curators at the Carnegie Museum.  But this specimen is especially cool because it was one of his first collections, collected in his hometown, years before he became curator.
 
Jennings (1877-1964) was born on a farm in Olena, Ohio.  He collected this species in Olena when he was 21 years old, the year he started as a student at the Ohio State University.  Jennings started his 60-year tenure at the Carnegie Museum six years later, in 1904. He made many contributions throughout his career, serving as the Curator of Botany, Director of Education, and eventually Director of the Carnegie Museum of Natural History.  He also was Professor of Head of the Department of Biological Sciences at the University of Pittsburgh, having advised many students.  His legacy remains to this day for his influence on the museum, botany, conservation, and environmental education.

Spring leaf out is a bit “behind” in Pittsburgh this year.  Well, for Norway maple in Schenley Park compared to 1948.  Plant leaf out and flowering times is variable for many species each year due to differences in spring temperatures. This Norway maple specimen was collected by Botany curator Otto Jennings.  Norway maple (Acer platanoides) is commonly planted across our region, common as a street tree or park plantings.  Norway maple is invasive in Pennsylvania, spreading into natural habitats. Its leaves superficially resemble the well known sugar maple but has a different leaf shape. Norway maple has even been put on the Canadian 20 dollar bill instead of the native sugar maple (http://www.cbc.ca/news/canada/ottawa/canada-s-new-20-bill-at-centre-of-maple-leaf-flap-1.1343767). A good way to tell it is Norway maple is that exudes a white latex from the leaf when picked.

Keep an eye out for Norway maple over the next week!  That light yellow/green you see at the tips of trees (especially along highways) in early spring is not tree leaves, but flowers. And many of these trees in urban areas around Pittsburgh are Norway maple.  Many trees flower early in the spring, before they leaf out.  Many tree species are primarily wind pollinated, so flowering before most species leaf out facilitates pollen to blow around with fewer obstructions.
 
In a long-term project initiated last year, we are recollecting specimens on the same calendar date and in the same location as historic specimens in the herbarium.  These recollections will grow the herbarium with future use in mind – permitting comparisons across time, such as changes in leaf out dates, flowering, and genetic works.  Long term studies (and herbarium specimens) are important to understand the effects of climate change and other human activities because of yearly variation.  Check back for more on this project!
 
Image below: Norway maple buds today on a tree in Schenley Park, Pittsburgh (Apr 4, 2018).  It is not quite ready to go. Note the buds are swollen but are not yet burst.  Compare this to the specimen collected in 1948, in full flower and early stages of leaf expansion.

​Over 90 years old and still beautiful color!  This red maple specimen was collected on October 23, 1926 by Otto Jennings during a field trip of the Botanical Society of Western PA to Chestnut Ridge in the beautiful Laurel Highlands of Pennsylvania.  Red maple (Acer rubrum) is one of the most common trees in eastern North America.  You can find it from southern Canada down to Florida and Minnesota down to eastern Texas. And it is renowned for its beautiful scarlet red foliage in autumn.  Happy fall!  

Both of these specimens were collected on May 17 in Highland Park– but 50 years apart. John Bright collected the specimen on the left in 1952.  Fifty years later to the day, Bonnie Isaac unknowingly recollected the same species in the same location! 
 
If you look closely, you’ll notice the 1952 specimen did not yet produce seed by mid-May, while the 2002 specimen has already started developing the characteristic maple-like seeds.  Due to increasing spring temperatures in recent decades, many plants tend to flower earlier, as shown through herbarium specimens. Botanists at the museum are studying the impacts of human-caused environmental changes over the past century by following in the footsteps of past collectors.  We are revisiting field sites on the same day to compare modern day plants to specimens collected over 100 years ago.
 
Sycamore maple (Acer pseudoplatanus) is a common forest tree in Europe, where they simply call it “sycamore” but should not be confused with our native and introduced sycamores.  Sycamore maple has been intentionally introduced across temperate regions, including the US and New Zealand.  It has since become invasive, meaning it actively spreads across the landscape and can cause ecological damage. It is less common than other invasive maples (such as Norway maple) in this region, but is invasive in several sites in the Pittsburgh area.