Bracts are specialized plant structures that serve varied functions such as attracting pollinators and protecting inflorescences (flower structures). Often leaflike, bracts range from the inconspicuous to the wildly showy. Perhaps the best example of the latter is poinsettia (Euphorbia pulcherrima), whose bright red bracts surround the inconspicuous yellow-green flowers and are often mistaken for petals. And, in fact, the bracts serve the same purpose that petals often do: attracting pollinators.
Several popular dogwood (Cornus) species also have prominent bracts that look quite petal-like and serve to attract pollinators. Flowering dogwood (C. florida), a North American native tree, blooms in early to mid spring with showy white or pink, notch-tipped bracts surrounding a tight cluster of tiny yellow flowers. Kousa dogwood (C. kousa), an Asian counterpart [pdf] to C. florida, has an extended bloom period from late spring into early summer. This species also has large white bracts but they have long pointed tips, giving the inflorescences a starry look. (Read this [pdf] for the interesting story of how monkeys may have affected fruit evolution in Asian large-bracted dogwoods!)
Lindens [pdf] (Tilia) have very distinctive narrow, leaflike bracts that are adnate to (merged with) the end of the flower cluster stalk. A stroll through the Arboretum’s linden collection over the coming weeks will provide not only the delightful scent of their flowers but also a good view of the bracts, which may serve as pollinator attractors (especially for nocturnal insects) and provide some winglike help in distributing the small nutlets in autumn.
And one more prized species at the Arboretum that’s noted for its bracts is the dove tree [pdf] (Davidia involucrata). The specimens in the Explorers Garden (5159-A, 14473-A) are real showstoppers when they bloom, with their ping-pong ball sized inflorescence cloaked by two large white bracts that account for the species’ common names “dove tree” and “handkerchief tree.” Research [pdf] has shown that the dove tree’s bracts have multiple functions, including attracting pollinators, especially bees, and acting as an umbrella that protects pollen from rain.
Nancy Rose, editor of Arnoldia