The Tulip Tree,(Liriodendron tulipifera), one of our largest native trees, is a member of the magnolia family. There may not be a more appropriately-named tree in all the land, for the likeness of its orange and yellow goblet-like flowers and the shape of its leaves to that of tulips is undeniable. Although large in size (2” in length) the flowers can go unnoticed because they are usually found high up on the 60 – 90-foot tree, and they don’t appear until the leaves are fully developed.
Tulip Trees flower for only two to six weeks. Pollination must occur when the flowers are young, and they are often receptive only for 12 to 24 hours. The flowers produce large quantities of nectar for pollinating insects such as flies, beetles, honey bees and bumblebees, but they are not very efficient pollinators and many seeds do not develop. Those that do form cone-shaped seed heads that may remain on the tree after the leaves have fallen.
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Nothing announces the arrival of spring more than willow flowers peeking their silver heads out of the bud scales which have surrounded and protected them all winter. What we call pussy willows are, in fact, the soft, silvery hairs that insulate the emerging spike of flowers, or catkin, within a willow flower bud. Pussy willows are dioecious, meaning there are both male plants and female plants. A male willow has only male catkins; female willows have only female catkins.
An individual willow catkin consists of all male or all female flowers. The first catkins to emerge in the spring are usually males. The hairs, or “pussies,” that emerge when willow buds first open trap the heat from the sun and help warm the center of the catkins, where the flowers’ reproductive parts are located. This trapped heat promotes the development of the pollen (or in female flowers, the ovules) of the flowers deep within the hairs. Eventually the reproductive parts of the willow flowers – the stamens and pistils – emerge, but until they do, we get to enjoy their silvery fur coats.
Early in spring, often in March, long before trees begin to leaf out, the swollen red buds of Silver Maple (Acer saccharinum) begin to open, revealing the flowers within. Typically, most of the buds on a given tree bloom at the same time; in fact, if there are several Silver Maples in an area, they will usually all flower within days of each other. Most of the flowers on any given tree are of the same gender, so there are male and female trees.
The flowers of maples are wind-pollinated and lack petals (which would hinder dissemination of the pollen). Therefore, the flowers are not large and flashy, and often escape notice. Flowering before leaves emerge also enhances pollen dispersal. The flowers are generally either male or female. If you look closely at the male flowers, what you will see are bundles of stamens, sometimes red and sometimes yellowish-green, tipped with yellow pollen. Female flowers have reddish clusters of pistils forming clumps of bristly little balls along the branches. The pistils develop petal-like extensions at the tips called stigmas, which are receptors for the pollen. (Photo: Silver Maple buds opening; inset = male Silver Maple flowers)
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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.)
Even though it snowed in Vermont this weekend, there is something else white and fluffy that is also being blown about, and it doesn’t melt when it hits the ground. The tiny white bits of fluff that are floating in the air are the seeds of aspens (also referred to as poplars), primarily Bigtooth Aspen (Populus grandidentata), that are borne in capsules that develop along a 3 to 6-inch dangling stem. These former flower clusters, and the capsules and seeds they developed into, are referred to as catkins. The capsules split apart when the seeds are mature, releasing the cottony-tufted seeds that are well-designed for dispersal by the wind. Looking into the fluff-filled sky, it’s not hard to believe that a single Bigtooth Aspen tree can produce over a million seeds.
Silver maple (Acer saccharinum) is second only to skunk cabbage when it comes to early spring flowering. Even with our nights still well below freezing, silver maple trees are bursting with blossoms. This close relative of red maple bears its male (pictured) and female flowers separately, sometimes on the same tree and sometimes not. Silver maple’s sap can be tapped and boiled into syrup, but the yield is much less, and it’s only about half as sweet as that of sugar maple.
Witch Hazel (Hamamelis virginiana) is in flower, one to two weeks early this year, just as last year’s fruit is mature and ready to explode, sending seeds flying. This shrub may have gotten its name from its association with dowsing, which was once thought to be a form of witchcraft. (Witch hazel’s branches were once the wood of choice for dowsing rods, whose purpose is to locate water, or “witch” a well.) The bark, leaves, and twigs of witch hazel are all high in tannins, giving this plant astringent properties. It has also been used for any number of medicinal purposes, from treating hemorrhoids to laryngitis.