Purple Leaf Plum

Prunus cerasifera

There is one purple leaf plum in the Park in the northeast triangle. See Wikipedia entry here.
Purple leaf plum in northeast triangle in June
Purple leaf plum factoids:
  • The scientific binomial name Prunus cerasifera means "cherry-bearing plum," since the fruit, when present, is small and resembles a cherry 
  • The plum tree blossoms very early in the Spring, and in this growth zone the blossoms precede the pollinators. If there is no pollination of the flowers, there is no fruit, so our tree will rarely bear fruit.
  • The genus Prunus includes about 430 species, including plums, cherries, peaches, nectarines, apricots, and almonds. Compare the plum flowers and leaves to those of the very similar cherries in the Park
  • Below are pictures of the leaves, bark, and flowers of our tree, plus a sketch of these components of the purple leaf plum
Flowers in early March
One of the few plums to fall off the tree, this one on June 12. Apparently, some of the flowers are pollinated. This plum variety is chosen more for looks than for fruit, and as the species name cerasifera suggests, this plum looks like a cherry (but tastes like a plum).
Botany 101 Bonus
Why are most trees, in fact most plants, green? Ask this of a random sample of people and you will get first a look of disbelief at the stupidity of the question, and then a look of puzzlement as to the answer. Almost all plants are autotrophs, meaning they can make their own food using carbon dioxide in the air, water in the soil, and the energy of sunlight. This sunlight comes in different wavelengths, which when combined give us the white light of the sun, but when separated by a prism or by raindrops, give us the separate colors of the rainbow.
This process of photosynthesis occurs in the leaves of a tree. The pigment in green leaves that is most prominent is chlorophyll. As the diagram below shows, the two chlorophylls, A and B, absorb mostly blue and red light and absorb little green light. This green light that is not absorbed is reflected, giving the green color.
There are accessory pigments called carotenoids that absorb some of the blue light that chlorophyll misses, which give them the colors yellow, red, or orange. These carotenoids give us the fall colors when the chlorophyll is broken down by the tree. Another pigment called anthocyanin is not involved in photosynthesis but gives stems, leaves, and fruits a red color. You would think that a red-leafed tree would be at a significant disadvantage in competition with green-leafed trees, but as it turns out, at high light levels there is not much of a difference in photosynthesis rates since the red-leafed trees do contain chlorophyll. At high light levels, the red anthocyanins may even offer some protection from harsh ultraviolet light. At low light levels, however, red-leafed trees are at a disadvantage. In fact, when purple leaf plum trees are planted in the shade, the leaves will be green rather than purple.
There is another reason red-leafed trees stick around despite a competitive disadvantage: humans like them! Humans select red-leafed trees as ornamentals and ensure their continued spread. A more familiar analogy would be asking why poodles and other domestic dog breeds persist in a world where there are wolves. Humans select for dogs, and up until recently, even tried to exterminate wolves. In nature, however, competition between wolves and poodles would be a bit one-sided.

Matthias Baldwin Park 

423 N 19th St 

Philadelphia, PA 19130

Friends of Matthias Baldwin Park is a 501(c)(3) nonprofit organization that works to preserve the Matthias Baldwin Park

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