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Flowering Trees

Focus your eyes above the woodland floor and examine the underappreciated flowers of spring.
A stroll through the woodland this month seems almost deafening in comparison to the muted undertones encountered for the past few months. From a barren branch overhead, a male cardinal proudly proclaims to all interested females that he’s staked out prime territory for this year’s nest. A shy Carolina wren loudly announces his presence with his rolling ‘teakettle, teakettle, teakettle” song. The melodious whistles of a pair of bluebirds announce that the pair has returned to nest in the box along the woodland edge.  

It slowly dawns on us that there is a faint greenish-yellow tint to the canopy. The stately sentinels of the forest are, too, proclaiming their reproductive exuberance. What were barren branches a mere week ago have awakened from their winter dormancy as succulent buds swell with emerging leaves and flowers.  

Some tree species—dogwoods, yellow-poplar and hawthorns—showily announce their presence, their unexpected splashes of colors seemingly gaudy in comparison to their many understated woodland counterparts. Here are a few examples of the variety of flowers found above the woodland floor. How many can you identify? 

Flowers on the white ash (Fraxinus alba) appear early in the spring, before the leaves emerge. White ash is dioecious, with individual trees being either male or female. Male trees typically bloom annually, but females bloom heavily only every few years. Both male and female flowers are approximately 1/8 inch across and yellowish green to greenish purple in color. Ash flowers are cross-pollinated by the wind, with one study citing pollen dispersal as much as 328 feet from the flower.  

A dioecious tree, drooping clusters of greenish yellow flowers appear on male and female boxelder (Acer negundo) trees before their leaves unfold. The flowers are wind-pollinated.

Flowers of the sassafras (Sassafras albidum) appear shortly before leaves develop, with male and female flowers borne on separate trees. Both sexes produce small, tightly clustered groups of greenish yellow to yellow flowers at the tips of twigs. Small bees and a variety of flies are responsible for pollination.
Fragrant yellow flowers—earning it the title the “forsythia of the wild”—emerge on both male and female spicebush (Lindera benzoin) plants in mid-spring. The ¼ inch flowers are pollinated by a variety of insects, including small bees and flies. 

Willows (Salix sp.) are dioecious, and the sex of a tree is known only by examining the structure of the flower, or by the seeds which will develop on a female plant. Flowers bloom in mid-spring, about the same time that leaves begin to develop. Both male and female flowers, called catkins, are 1-3 inches in length, narrow and cylindrical in shape and greenish in color. Insect pollinators include bees and flies. Wind pollination also may be possible. 

The Ohio buckeye (Aesculus glabra) is monoecious, meaning that male and female flowers occur separately on the same plant. Large, showy clusters of yellow-green flowers, sometimes nearly a foot in length, appear in April and May. In addition to a variety of bees, these flowers are pollinated by the ruby-throated hummingbird.

Yellowish male flowers of members of the oak (Quercus sp.) family appear first as a 2-3 inch long catkins, followed a few days later by the emergence of minute, reddish female flowers in the axils of the leaves. Flowers are wind-pollinated.
The monoecious sweetgum (Liquidambar styraciflua) produces both male and female flowers on the same tree. Male flowers are about 1-2½ inches long, greenish yellow in color and present in ascending clusters. Female flowers occur as a green, globe-like head that droops from a stalk. The flowers are pollinated by the wind.

One of the first trees to flower each year is the silver maple (Acer saccharinum), whose pendulous, wind-pollinated red flowers appear before leaves begin to emerge. Silver maple trees may be monoecious or dioecious, and some trees are able to change their gender from year to year.

Fragrant flower clusters appear on the black locust (Robinia pseudoacacia) from late spring to early summer, after the leaves have fully developed. Individual pea-like flowers occur along a 4-6 inch long dropping cluster and are white with a small, yellow spot. Bumblebees are the primary pollinator for locusts, although flowers also are visited by honeybees, butterflies, moths and ruby-throated hummingbirds.
Rose-purple clusters of flowers appearing on the red bud (Cercis canadensis) tree mark the start of spring for many people. The ½-inch long, pea-like flowers grow not only on the branches of the tree, but also on the trunk, and appear before the leaves unfold. Numerous species of bees are responsible for pollination of the red bud.

The largest solitary flower of trees native to Illinois belongs to the yellow-poplar (Lirodendron tulipifera), perhaps better known by alternative common names, the tulip-poplar or tuliptree. The showy, cup-shaped flowers open in April and May after the leaves unfold. About 2 inches in length, each flower possesses a cone-shaped cluster of pistils (the female structure) surrounded by six petals, yellow-green in color except for a band of orange at the base. Nectar-laden flowers attract numerous insect pollinators, including flies, bees and beetles. 

A perennial favorite of many, dogwoods (Cornus sp.) punctuate the woodland with flowers from April to June—but what many call the flower really isn’t. The actual flower is a small cluster surrounded by what many mistake for petals, but actually are called bracts. The short-tongued bee (Andrena fragilis) is a specialist pollinator of dogwood flowers. Also attracted to the nectar and pollen are numerous other types of bees, as well as several species of flies, butterflies and beetles.  

The early profusion of blossoms on the white-flowered serviceberry (Amelanchier sp.) is a welcome sign of spring. Groups of 6-14 five-petaled flowers hang from the tips of branches. These mildly fragrant flowers are pollinated by bees, flies, beetles and other insects.         

Hanging pendulously from branches in mid- to late-spring are the reddish-purple flowers of (Asimina triloba), or the paw paw. Composed of three sepals, three inner petals and three outer petals (hence the species epithet triloba), the flowers have a slightly offensive odor that attracts a number of flies, included flesh and blow flies.


By: Kathy Andrews
Red bud flowers