May 032019

The flowers of our common trees are an under-appreciated element of spring’s beauty

A beautiful spectacle unfolds above our heads each spring. The lengthening days and increasing warmth are stirring flower buds that have lain dormant through the long winter months. Where only weeks ago there were just bare branches, the flowers of many of our most common trees now punctuating the landscape and offering up a gentle array of colours and shapes. As the flowers open, tree crowns take on a hazy, pastel appearance, announcing the long-awaited change of season. Make a point this spring of looking up and appreciating this blossom parade that can easily go unnoticed.

Flower parts 101

Like the annuals and perennials in our gardens, all trees produce flowers. Their raison d’etre, of course, is to produce seed to assure future generations. Flowers, however, vary in their configuration and can’t be fully appreciated without knowing the various parts. This might require reacquainting yourself with some special vocabulary. Let’s start with a typical or “perfect” (hermaphroditic) flower, such as those of a cherry or apple tree. A typical flower has both male and female reproductive organs together in the same structure. The female part is the pistil, which is usually located in the center of the flower and rises above the male parts. The pistil consists of the stigma (the sticky, widened top), the style (the long tube holding up the stigma) and the ovary, which is hidden at the base of the style. The ovary contains the female egg cells called ovules.

The male parts are called stamens and usually surround the pistil on all sides. The stamen is made up of the anther (the widened, pollen-producing top) and the filament, which is the stem of the anther. When a flower is pollinated (fertilized), pollen adheres to the stigma, and a tube grows down the style and enters the ovary. Male reproductive cells travel down the tube and fertilize the ovule, which then becomes a seed. The ovary becomes a fleshy fruit. Remember this the next time you eat an apple, because you are actually eating an apple flower’s enlarged ovary. Because insect activity is so unpredictable during the often-cool days of April and early May, most early‑flowering trees depend primarily on the wind to spread their pollen.

Not all flowers are “perfect”, however. Flowers may also be unisexually male and only bear pollen-producing stamens (staminate flowers) or unisexually female and only bear seed-producing pistils (pistillate flowers). Unisexual flowers often appear in long, caterpillar‑like structures called catkins. Each catkin contains dozens of individual flowers – all male or all female. Think of a cob of corn and each tiny flower as one kernel on the cob. Some common trees with catkins include willows, poplars, aspens, alders, and oaks.

The parts of a flower (Drawing by Judy Hyland)

Male catkins of Speckled Alder – Drew Monkman









Because catkins are easily jostled by the breeze, they are a superb adaptation to wind pollination. Let’s take the example of the Speckled Alder, whose catkins light up local wetlands. In the warm April sunshine, they swell into eight-centimetre-long purple, red and yellow garlands, releasing their pollen in golden puffs when disturbed. The female flowers are nestled in small, erect catkins that become cone‑like in appearance when the seeds are ripe.

One house or two?

Like human sexuality, the sex of trees – male, female or both – is complicated. Some species have separate male and female flowers on each individual tree. That is, one branch or twig might male flowers and another have female flowers. These species, along with species possessing the more typical “male and female together” flowers (a.k.a. perfect flowers) are referred to as monoecious (from the Greek, in one house).

However, there are also plants like willows, poplars, aspens, hollies, and Manitoba Maples that have separate sexes, just as animals do. They have male flowers on male plants and female flowers on female plants. These species are called dioecious (in two houses). This means that female trees can only produce fertile seeds if there is a male nearby. Hollies are an example that gardeners are familiar with. An individual holly is either male or female and produces either functionally male flowers or functionally female flowers. The word “functional” is important here, because sterile, reduced-in-size, non-functional flower parts of the opposite sex are present in both the male and female flowers of hollies.

Even within the monoecious/dioecious framework, there are exceptions. In the case of Red Maples, for example, some individual trees are monoecious, and others are dioecious. Under certain conditions an individual Red Maple can even switch from male to female, male to hermaphroditic (perfect flowers), and hermaphroditic to female.

The flowering calendar

Trees and shrubs flower in reliable order each spring. With climate change, however, the dates have tended to become earlier on average.

Late March: Silver Maple, poplars, aspens; Early April: Red Maple, Speckled Alder, Pussy Willow;

Mid-April: American Elm; Late-April: Manitoba Maple, White Birch; Early May: Serviceberry (Juneberry); Mid-May: Sugar Maple, Norway Maple, Common Lilac, Pin Cherry, apples;  Late May: Striped Maple, White Ash, Chokecherry; Early June: Bur Oak, Red Oak, American Beech; Mid-June: Black Locust, Black Cherry, Black Walnut; Late June: Catalpa, Small-leaved Linden; Early July: American Basswood

The maples

Each spring, I like to pay special attention to the flowers on maples. The Silver Maple is the first of this genus to blossom, with flowers often appearing as early as March. The fat, bright clusters of red flower buds produce either male flowers with dainty yellow stamens or female flowers with reddish pistils. When the male flowers are ripe with pollen, the whole twig looks yellow. Twigs with female flowers appear all red when the pistils appear.

In early April, Red Maples have their turn. The profusion of tiny, red flowers against the tree’s smooth gray bark is one of spring’s loveliest sights. The flowers have small, red petals, which hang in tassels. The Red Maple wears its name proudly, because all the tree’s interesting features are indeed red: the winter twigs and buds, the spring flowers, the leafstalk and, in male trees especially, the fall foliage. In the Kawarthas, Red Maples are primarily a Shield species. Both Red and Silver Maples attract bees on warm spring days, thanks to their offering of pollen and nectar. They are also pollinated by the wind, however.

A cluster of male flowers (L) from a Sugar Maple. Three female flowers, each with two long styles, can be seen at the bottom on the cluster on the right. (Drew Monkman)

Another member of the maple clan to flower in April is the Manitoba Maple, a somewhat aberrant member of the genus. Not only does it have ash‑like, compound leaves, but the seed flowers and pollen flowers appear on separate trees. This is a very common species of urban areas, taking root in some of the most inhospitable sites imaginable

In the next couple of weeks, Sugar Maples will be flowering. To the trained eye, blooming Sugar Maples are one of the most conspicuous trees in both the urban and rural landscape. The trees glow in a garb of pale yellow-green as countless, long-stalked clusters of flowers hang from the twigs. At a glance, the floral display might be mistaken for leaf-out, but the leaves have usually only begun to emerge when Sugar Maples are in full flower.

The male and female flowers of Sugar Maples can appear on separate trees, on separate branches of the same tree, or even on the same branch in the same tree in the same cluster. There are no petals on the flowers. Clusters of male flowers are 7-10 centimetres long with hairy stalks. Each cluster has 8-14 individual flowers. At the end of each stalk is a bell-shaped, yellow-green calyx. Six to eight stamens extend just beyond the calyx. Most of the flowers low on the tree are male.

Female flowers appear in shorter clusters, measuring only 2-5 centimetres in length. The pistil has two curved styles, which protrude from the calyx. Female flowers are most common higher up in the tree. Within a week or so, the male flowers fall to the ground, leaving a yellow confetti on sidewalks and roads. Female flowers, of course, develop into paired keys, which spin to the ground in late summer.

Norway Maples, which also bloom in mid-May on average, also deserve a close look. The flower clusters resemble giant, lime-green pompoms. The leaves and flowers emerge simultaneously. Unlike the Sugar Maple, the flower clusters are erect, and each flower has five petals. Male flowers are composed of eight fertile stamens, while female flowers have eight sterile stamens and a long green pistil, which splits into a pair of curved styles.

The flower clusters of Norway Maples, sometimes resemble giant, lime-green pompoms. Drew Monkman

I encourage readers to take some time this month to look more closely at tree flowers. It’s fun to try to see all the floral parts and to determine whether the flower is male, female or a perfect flower combining both. Try to follow the progression on female flowers from blossom all the way to seed, maybe capturing the development with your camera.  Nature reveals so much more when you take time to really pay attention.





Arguments for Climate Action

              When talking about climate change with friends and family, remind them that a majority of Canadians in every province, except for Alberta and Saskatchewan, are in favour of a carbon tax.  A majority also believes that government must lead the climate effort and that individual action won’t be enough. When people say, “Well, what can I do?”, the answer is simple: support strong government action. In addition to a carbon tax, this includes phasing out coal and implementing stronger regulations like more aggressive clean fuel standards. Point out that 70 percent of Canada’s emissions are industry-related. All these initiatives, of course, involve costs to taxpayers – either transparent at the gas pump or hidden when it comes to regulations affecting industry – so paying these costs is “what you can do”. 






May 012014
Serviceberry (Drew Monkman)

Serviceberry (Drew Monkman)

Although the flamboyant reds, yellows and oranges of fall always receive the most attention, there is an equally beautiful showing of colour in May. From the radiant white blossoms of serviceberries and trilliums to the fresh, lime‑green leaves of sugar maples, May paints the landscape with a gentle warmth all its own. And, unlike many phenomena in nature, the transformation of the landscape from grays and browns to greens, whites, yellows, purples and pinks, is easily observed by all.

The order in which the various species of plants bloom and come into leaf is the same each year. Although variations in weather conditions may accelerate or slow down the process, the general sequence does not change. The first herbaceous plant to flower in spring in the Kawarthas is Coltsfoot, a yellow‑blossomed, dandelion-like denizen of roadsides. Usually by mid‑April – but only just starting this year -, the first true woodland flowers appear, beginning with Hepatica and followed shortly after by Bloodroot, Blue Cohosh, Trailing Arbutus and Marsh Marigold. As we move into early May, dozens of other species join the blossom parade including Common Dandelion, Spring Beauty, Trout Lily, Large-flowered Bellwort and various species of serviceberry (Juneberry). By the middle of the month, we can expect to find Common Lilac, White Trillium, Red Trillium and Pin Cherry all in bloom. And, by late May, Mayapple, Jack‑in‑the‑Pulpit, Wild Columbine, Choke Cherry, Red‑osier Dogwood, the various hawthorns and the first orchids will be flowering.

All of our trees produce flowers, too, even though they often go unnoticed and unappreciated. Red and Silver maples, which have been in flower for several weeks now, have been joined in recent days by White Birch and American Elm. Take a moment to look closely at the flowers on low-hanging branches and you will see dainty floral parts tinged with pastel reds, yellows, browns and greens. In the next couple of weeks, Sugar Maple will be flowering, as well. This is a spectacle not to missed. These trees literally glow in a garb of pale yellow as tens of thousands of tassel-like flowers hang from the twigs. Within a week or so, the male flowers fall to the ground, leaving a yellow confetti on sidewalks and roads. Norway Maples, which bloom at about the same time, look like giant, lime-green pompoms. Their leaves and flowers emerge simultaneously. Soon after the maples, the oaks, too, will be in flower. The caterpillar-like male flowers (catkins) are as long as the emerging leaves. Mid-May also sees the appearance of flowers cones on pines, spruces and larches. The purple-pink female cones of the American Larch (Tamarack) are especially beautiful.

The leaf‑out of trees and shrubs follows a predictable sequence, too. Red‑berried Elder is the first species to come into leaf, usually in late April. Early May brings us the leaves of Manitoba Maple, Norway Maple, Trembling Aspen, Common Lilac, willows and both Pin and Choke Cherry. Sugar Maple, Bigtooth aspen and Tamarack leaf out in mid‑May, while Red Maple, American Basswood, oaks, elms and ashes wait until later in the month to produce their leaves. As the trees leaf out, take time to appreciate all of the different shades of green that grace the landscape. Among my favourites are the shiny, light greens of aspens and the gentle, pastel tones of new Tamarack needles.

Coltsfoot - Drew Monkman

Coltsfoot – Drew Monkman

In addition to the spectrum of greens, white is another signature colour of May. Early in the month, serviceberries stand out like white beacons against the slowly greening landscape. These small trees grow in clumps and are common along roadsides and field edges. We tend to notice them only in the spring, however, when their beautiful masses of white, five‑petal flowers burst forth. Belonging to the genus Amelanchier, they also go by the name of Juneberry, because their fruits ripen in June. Later in the month, Pin Cherries and Choke Cherries add their own splashes of white. They tend to grow in the same habitat as serviceberries. Cherry leaves are unique in that they are tinged with bronze‑orange when they emerge. Hawthorns, a species of old fields, and Red‑osier Dogwoods, a shrub of wetland edges, complete the white blossom parade. Many of our wildflowers also have white blossoms. The White Trillium is certainly the best known. Standing nearly a foot tall and flaunting flowers three or four inches across, trilliums form a carpet of white over the forest floor, that is hard not to notice. This species is well‑named with its three leaves, three petals and three sepals.

Yellow is another common colour this month. And, any discussion of yellow leads directly to the Common Dandelion. Introduced from Europe, dandelions provide copious amounts of pollen and nectar to insect visitors. Insects see the flowers as shining points of ultraviolet light set against a green background, which they perceive as grey. Dandelions are largely responsible for the first honey of the season, thanks to their attractiveness to honey bees.

Yellow flowers also turn up in wet habitats in early spring, thanks mostly to Marsh Marigolds, also known as cowslips. In the unblocked sunlight, they grow up to 18 inches tall and have huge, heart‑shaped leaves. The flowers usually have five petals. The swampy woods along University Road, just south of Nassau Mills Road, is a great place to see them.

It is believed that white and yellow are particularly efficient colours at reflecting sunlight from a plant’s petals onto the central reproductive parts of the flower. This helps to accelerate the development of pollen and seed in the cool spring weather. The heat that accumulates in this manner may actually raise the temperature inside a trillium or marigold several degrees above the surrounding air. Insect pollinators probably find the slightly warmer temperatures of the flowers very much to their liking, as well.

For many of us, May is also synonymous with the purple blossoms of lilacs. Lilac bloom times and leaf emergence have long been monitored in both Canada and the United States, since they are examples of natural events whose timing can be influenced by climate change. On average, lilac leaves now emerge in the northern hemisphere about five days earlier than they did 50 years ago.

In order to see the whole flower show, you will need to be out looking at least once a week. Woodland plants in particular have a very short blooming period. Their life cycle is attuned to the rhythms of the forest canopy. Once the leaves have fully emerged, most flowers quickly disappear. The light available on the forest floor for photosynthesis quickly falls to 1% of the level at the top of the canopy. In the deep shade of the inner forest, plants struggle to produce enough food even for their own needs, let alone having food left over for the purpose of flowering and seed maturation. Species like trilliums are therefore engaged in a veritable race against the clock to bloom, attract pollinators and build food reserves through photosynthesis before the canopy closes.

Young female flower cones of Tamarack - Drew Monkman

Young female flower cones of Tamarack – Drew Monkman

Two of the better places to see woodland plants include Mark S. Burnham Provincial Park on Highway 7, just east of Peterborough, and the Emily Tract forest, located in the City of Kawartha Lakes on Victoria County Road 14, west of County Road 10.