Eastern Redbud

Cercis canadensis

There are six redbuds in the Park, most easily identified in April. See Wikipedia entry here.
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Redbud in the southeast triangle, looking northward.
Redbud factoids:
  • Easily identified in the spring by its exuberant red buds, and in the summer by its heart-shaped leaves and flat seed pods. See the article on the katsura tree for comparison here.
  • Deciduous, often multitrunked
  • Commonly called eastern redbud
  • The genus name comes from the greek work kerkis meaning weaver's shuttle, for the seedpod's resemblance to the shuttle
  • There are many different cultivars within the species. Cultivars are interbreeding varieties within a plant species, analogous to breeds in dogs.
  • The reddish-purple leaves change to dark green in summer, and then to yellow in the fall.
  • Flowers and seed pods are edible.
  • The species of redbud in the Mediterranean, called Cercis siliquastrum, is commonly called the Judas tree because legend has it that Judas hung himself from a redbud after his betrayal
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The same redbud as seen in the prior photo, at its planting in 2008.
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Pair of multitrunked redbuds in the southwest triangle, looking southward in June.
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Copious seedpods on redbud in southwest triangle in late June.
The seed pods look like weaver's shuttles.
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Flowers very close to branches and trunk in April, before leaves appear, from tree in west triangle
The botanical term "cauliflory" refers to flowers and fruits growing directly out of the old growth branches, and not on new buds at the end of the stem. The redbud is one of the few temperate region trees that displays cauliflory. Note the seed pods hanging directly off the branches in the photo above.
 With close inspection you may notice cauliflory on the female katsura, with fruits on mid-branch. See outside link here for more on cauliflory.
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Redbud in northwest triangle, in July, looking northward
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Redbud in west triangle, looking east, in April
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Redbud in northeast triangle, looking north, in July.
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Reddish tint to inner bark on a redbud in July
Botany 101 Bonus
 
As noted, the redbud flowers in late March before the leaves appear. But how does it know to break bud at this particular time? Is it temperature? Is it light? If it flowered during a warm spell in January, the February cold would kill the new flowers.
Just as you have photoreceptors (light detectors) in your eyes, so too do plants have light detectors called phytochromes. Most plants detect seasonal changes via these light receptors that detect the day length. Once the daylight extends for 12 hours, for example, some species will flower. What the plants are really responding to is not a longer day, but a shorter night. In experiments, if you shine a light on plants for even a brief period during the night, they will not flower no matter how long the day. So a short night is one factor. 
Another factor for many plants is temperature. When the temperatures warm, and only after a cold spell, then the buds will break. This cold spell might be three weeks below just 42 degrees F, so somehow the plant knows how to sum up accumulated cold days. This combination of shorter nights and warmer temperatures after a cold spell triggers even the bulbs planted underground in the autumn.