Striped Maple (Acer pensylvanicum), named after the vertical white streaks on its bark, is often associated with Moose and White-tailed Deer, both of which feed on its bark. In some places it goes by the name “Moosewood” for this very reason. The shape of its leaves give it another common name, “Goosefoot Maple.” In the spring when Striped Maples are nearly in full leaf, bright yellow bell-shaped flowers appear on long, pendulous strings, or racemes. (The flower stalks of the similar Mountain Maple also materialize after the leaves have matured, but these flower clusters are upright, held above the surrounding leaves.)
Striped Maples have the unusual ability to change sexes repeatedly over their lifetime (as does Jack-in-the-Pulpit), a phenomenon called gender diphasy. Among five study populations located in New Jersey, approximately one in four trees exhibited a change in the sex of its flowers between flowering seasons. The flowers of most Striped Maples are predominantly male. If changes occur in the canopy and new conditions seem favorable, a predominantly male tree can become predominantly female (and vice versa, if conditions deteriorate). Size, injury, and carbohydrate reserves are thought to impact the frequency and direction of gender change. Another unusual trait of Striped Maples is that the final sex of a flower is determined within one month of flowering, in contrast to most woody perennials which set buds the previous year.
In 1935 Walter Rogers wrote a book on tree flowers (Tree Flowers of Forest, Park and Street) in which he described White Ash (Fraxinus americana) in the following words. “The Ashes are important trees with interesting features of form and foliage, but their flowers are among the least interesting.” I am of a different opinion, at least regarding White Ash’s male, or staminate, flowers.
White Ash is dioecius – individual trees have all male or all female flowers. Just before and as the tree is leafing out, the flower buds, located on the shoots of the previous season, begin to open. Male flowers are more noticeable than female flowers, partly because of the size of their clusters — there are between 200 and 300 flowers in each cluster – and their vibrant color (which resembles the fall color of some White Ash leaves). Being wind-pollinated, White Ash’s flowers lack petals as they would impede pollination. The stamens are a purplish-red, raspberry-like color until they mature, at which time the pollen’s yellow color is predominant. The flowers are soon hidden by emerging leaves, so now is the time to see if you agree with Mr. Rogers!
Aspens, cottonwoods, poplars – all are names for certain species of trees in the genus Populus. These trees, as well as birch, hickory, oak and willow trees, produce their flowers on spikes called catkins. Telling the catkins of these trees from one another is challenging, to say the least, yet some of NC’s readers correctly identified the catkins in the photograph as those of Bigtooth Aspen, Populus grandidentata. This tree blooms for one to two weeks in the spring and its mature male catkins open and extend to two to four inches in length. The wind, as opposed to insects, disperses the light, fluffy yellow pollen as the catkins dangle in the breeze. Some of the pollen remains intact even after the tree has shed its spent catkins onto the ground.
Because Bigtooth Aspen, and most species of Populus, are dioecious (male and female flowers develop on separate trees), there are only male flowers in this photo and beneath this tree. After fertilization, female flowers remain on the tree and form capsules which contain several small seeds embedded in tufts of fine, white hair. They will fill the air in several weeks looking like bits of floating cotton.
Red Maples (Acer rubrum) are celebrated in the fall for their vibrant colors, but they produce equally vibrant reds and yellows in early spring when they are flowering. Most Red Maples have dense clusters of either male flowers or female flowers (dioecious), although some have both male and female flowers (monoecious). Under certain conditions, a Red Maple tree can sometimes switch from male to female, male to both male and female (hermaphroditic), and hermaphroditic to female.
The showier male, or staminate, flowers contain between four and twelve stamens, with long, slender filaments and red (young) or yellow (mature) anthers at their tips. Both red sepals and petals can be seen at the base of the stamens. A staminate Red Maple in full bloom is a blaze of gold and red. (Photo: mature staminate Red Maple flowers)
Witch Hazel (Hamamelis virginiana) is nature’s final fanfare of the fall. As colorful fall foliage begins to disappear, the yellow strap-like petals of Witch Hazel’s fragrant flowers brighten denuded woods. This year, with a somewhat late peak foliage, they are both providing brilliant colors to the landscape at the same time.
Witch Hazel flowers are pollinated by moths that are still active this late in the season, and develop into small, hard capsules that remain dormant throughout the winter. During the following summer, these capsules develop to the point where they expel two shiny black seeds 10 to 20 feet away from the tree. The seeds take another year to germinate, making the length of time from flowering to germination approximately two years.
Witch Hazel (Hamamelis virginiana) is nature’s final fanfare of the fall. As colorful fall foliage disappears, the yellow strap-like petals of Witch Hazel’s fragrant flowers brighten denuded woods. These flowers are pollinated by moths that are still active this late in the season, and develop into small, hard capsules that remain dormant throughout the winter. During the following summer, these capsules develop to the point where they expel two shiny black seeds 10 to 20 feet away from the tree. The seeds take another year to germinate, making the length of time from flowering to germination approximately two years. (In photo, the yellowish-tan capsules were formed this summer, and the one brown, year-old capsule has opened and dispersed its seeds.)