Late fall is a great time to get to know these enigmatic structures
I’ve always loved November. Maybe it’s the change of pace and the sense of nature slowing down. Yet, we do notice changes. As deciduous trees shed their leaves, our eyes are drawn to the conifers like at no other time of year. They stand out in all their green splendor and beautiful shapes. And, if you look closely, you’ll notice something special this year: they are laden with a huge crop of cones.
You’ve probably held them, maybe used them to make a holiday wreath, but how many of us really know what cones are? The short answer is that cones – named after their shape – are the reproductive parts of an ancient branch of plants known as gymnosperms. Conifers form the largest group of living gymnosperms, but gingko trees also belong to this class of plants. About 300 million years ago, the gymnosperms became the dominant trees on the planet. They continued their dominance throughout the Triassic and Jurassic periods – the age of the dinosaurs. Their cones were even a favourite food of species like duckbill dinosaurs. The gymnosperms reigned supreme until the rise of the angiosperms – the flowering plants – during the Cretaceous period.
The arrival of gymnosperms was revolutionary, because it heralded the advent of the seed. This was as profound an evolutionary event as the development of the shelled egg in reptiles. Just as the egg allowed reptiles to become the first truly terrestrial vertebrates – and break nearly all aquatic ties – the evolution of the seed meant that plants no longer had to grow in moist environments like their fern and moss ancestors did. They could therefore colonize upland habitats. The gymnosperms protected their embryos from drying out by encasing them in a tough waterproof seed coat.
A closer look
All conifers produce cones. In fact, this is where the name “conifer” comes from. It is not accurate to call these trees evergreens, because some species, the tamarack for example, actually shed all of their needles in the fall, just like a maple or an oak. And not all cones are pine cones. This term only describes the cones of the pine tree. The cones of the other conifers should be named according to their parent tree.
Gymnosperms are different from angiosperms in that they lack true flowers. There are no petals, stamens, pistils or ovaries. In fact, the word gymnosperm actually means “naked seed”, because the seeds are not enclosed in an ovary. They simply develop from an ovule (egg) located on the inner surface of each of scales. Flowers, on the other hand, are produced by angiosperms, which include everything from oaks and maples to grasses and daisies. Angiosperm seeds develop when a pollen grain adheres to the stigma at the top of the pistil, travels down through the style and fertilizes an ovule located in the ovary. When you eat an apple and spit out the seeds, you are eating the enlarged ovary.
Male vs. female
As is the case with many flowers, cones can be either male or female. Both usually occur on the same tree. Junipers are an exception, having separate male and female trees. Let’s look at the female cone first. These are the typical hard, brown, woody cones. They consist of a central stalk surrounded by stiff, overlapping scales, reminiscent of wooden shingles. The ovules, which when pollinated become seeds, are located at the base on the inner surface of the scale. If you pry open the scales of a mature cone before it falls from the tree, you can often see the seeds inside. In white pine and balsam fir, the female cones are located high up in the tree at the tips of the branches. In most other species, they are found lower down, as well.
The male cones, also known as pollen cones, are much smaller (often only a centimetre or two in size) and far less conspicuous structures. Usually located on the lower branches, they are most often brown or reddish and resemble little spikes or buttons. They have a central axis, which bears pollen-producing structures. You’ve probably brushed up against them, causing a smoke-like cloud of pollen. Soon after the pollen is released, the male cones whither and drop from the tree. You will often see piles of male cones under pine trees in early summer.
Each conifer species follows its own reproduction timetable. In the case of the white pine, Ontario’s provincial tree, clusters of male cones first appear in the spring at the base of new twig growth. A few weeks later, the soft, green and purplish female cones emerge. At the time of pollination, they are about two centimetres long. Towards the middle of June, the male cones release their pollen grains. The grains are so well adapted to wind pollination that they actually contain two air bubbles. Only an infinitesimally small amount of pollen ever makes it to the female cones, however. Most of it simply descends from the sky turning cottage decks, shorelines and puddles a lemon yellow.
At the same time as the pollen is released, the female cones become receptive to receiving the airborne sex cells. The tiny cone scales open slightly and a small amount of fluid is secreted which serves to “trap” the pollen and draw it in towards the two ovules at the base of each scale.
Having secured pollen, the scales begin to thicken and to press tightly together. The cone continues to grow, hardens and turns from green to brown. Strangely enough, the actual fertilization of the ovules by the pollen only occurs 13 months later. It then takes an additional 13 months or so for the seeds to mature. In late summer, the scales dry out, flex backwards and open up one final time. This allows the seeds inside to simply escape to the wind. Each seed has a tiny wing, which helps it to float on the air, travelling up to 200 metres from the parent tree. In all, the process of reproduction will have taken over two years. The cones themselves drop off the tree during the late fall or winter, a few months after seed release. You can find them on the ground right now under almost any white pine.
Cone and seed development in all of the other conifers requires less than one year. In the case of white spruce and eastern hemlock, for example, the cones open and shed their seeds during their first fall or winter. The seeds often litter the snow. Spruce cones drop from the trees during this same period, but the cones of the hemlock remain on the branches until spring. White cedar cones also open in the fall and shed their seeds over several months.
With balsam fir – the best choice for a Christmas tree – the process is quite different. The scales themselves drop off the cone while it is still on the tree, thus liberating the seeds to the wind. All that is left is the bare, stick-like core of the cone. It can remain on the tree for several years. Balsam fir cones grow in dense groups near the top of the tree and stand straight up like candles.
In some conifers like junipers and yews, the scales on the female cone swell up and fuse together after pollination. This leads to the formation of a small, soft, fleshy cone, which superficially looks like a berry. You may have noticed the huge number of blue, berry-like cones on junipers (e.g., eastern red cedar) this year. Each contains one to four brownish seeds. Red cedar “berries” are very popular with birds like waxwings and robins.
Cones are a testament to the wonder of evolution. The arrangement of the spirals of scales, for example, is anything but random. They follow nature’s numbering system, known as the Fibonacci pattern. It goes like this: 1, 2, 3, 5, 8, 13, 21, 34… (each subsequent number being the sum of the two preceding ones). If you look closely at a pine cone, you’ll see a double set of spirals, each going in a different direction. When these spirals are counted, the two sets are found to be adjacent Fibonacci numbers. For example, you might see eight spiraling counterclockwise and 13 spiraling clockwise. Larger or smaller cones can have different pairs of numbers. No, trees are not mathematicians. This arrangement is simply the best use of space, so it has been favoured by evolution.
For a great holiday activity, you might want to try making a cone wreath. Going out to gather the cones themselves is half the fun. Try to find cones from different species. You’ll also need to make a cardboard base. The base can be cut into any shape you like – maybe a snowflake. Paint the cardboard or glue on a piece of felt. Then, using a glue gun, attach the cones to the base. If you spray the cones with water several hours before you begin, the scales will usually close and be easier to work with. Glue on the larger cones first, and then fill in the remaining spaces with the smaller ones. You can also add accents such as acorns and sumac berries. After the cones have fully dried and the scales reopened, spray the wreath with a clear lacquer. Handled with care, it will last for years and be a beautiful holiday reminder of the fascinating biology of cones.