Flowering of the Dogwood

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Image credit: Curious Sengi.

Blooming of the dogwood trees is a portentious sign that spring, at long last, is finally here to stay.

The tetrad of creamy white or pink-petaled flowers are not actually flowers at all, but specialized leaves called bracts.  Bracts are usually found as associated supports to flowers and other reproductive structures.  The true flowers are at the center of this arrangement and unfurl as a cluster of tiny yellow blossoms.  In the early autumn, these clusters transform into bright red drupe fruit.

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Image credit: Curious Sengi.

Within the United States, you are most likely to see a cultivar of Cornus florida.  This popular ornamental tree has a native distribution throughout the eastern part of the country from Maine to Florida.  Dogwoods are shade-tolerant denizens of the understory that grow interspersed with other trees forming the canopy above them.  Despite this modest standing, dogwoods are an important component of the local ecosystem.  Their leaves decompose rapidly, releasing mineral nutrients and improving the neighboring soil.  Dogwood fruits, flowers, leaves, and bark are all particularly rich in calcium and fat for the animals that feed on them.  The fruit alone are known to feed over 30 bird species and many mammals.  The wood is hard and smooth-grained, making it desireable as a fine craft wood and for making tool parts subject to heavy usage.

Cedar Waxwing (Bombycilla cedrorum) enjoying some fruit of the Flowering Dogwood (Cornus florida). Image credit: Gypsy Flores via Birds & Blooms.

Cedar Waxwing (Bombycilla cedrorum) enjoying some fruit of the Flowering Dogwood (Cornus florida). Image credit: Gypsy Flores via Birds & Blooms.

The evolutionary history of the whole dogwood clade was a biogeographical mystery, an unknown saga of worldwide meanderings now reconstructed from molecular, morphological, and fossil data.  There are about 58 species in the genus Cornus today and they are distributed in temperate and subtropical regions of North America, Europe, Africa, East Asia, and a sole species outposted in South America.  Earlier studies had suggested an Asian origin for dogwoods, but a recent study incorporating fossil material point towards a European birthplace.  Dogwoods arose in Europe during the Early Paleocene or Late Cretaceous, around 65 million years ago, and within a span of about 10 to 20 million years, the trees made multiple trans-Atlantic dispersals to North America.  The lone South American species was a result of migration from original colonizations in the north.  Though Europe and North America were much closer together during the Paleocene, when the young Atlantic ocean had yet to push the two continents away as distant as they are now, the exact mechanism of how dogwoods could travel over the salt waters has yet to be explained.

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Image credit: Curious Sengi.

 

References

McLemore, B.F.  1990.  “Cornus florida L.  Flowering Dogwood.”  In Silvics of North America:  Volume 2, Hardwoods.  United States Department of Agriculture.  Pp. 278 – 283.

Xiang, Q.-Y. et al.  2006.  “Species level phylogeny of the genus Cornus (Cornaceae) based on molecular and morphological evidence — implications for taxonomy and Tertiary intercontinental migration.”  Taxon 55 (1):  9 – 30.

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