Exploring Conifers

By Jon Peter, Curator & Plant Records Manager, Royal Botanical Gardens.

As we approach the holiday season and winter ahead, there is one division of plants which gets a little more attention at this time of year — conifers.

Conifers are a group of seed plants with descendants from more than 300 million years ago, much older than the descendants of flowering plants (and before dinosaurs roamed the earth). Conifers are found on every continent except Antarctica and there are approximately 550 species globally. They are very common especially in the northern hemisphere

The name conifer means ‘cone-bearer’. Conifers are distinct from other seed-bearing plants by their needle- or scale-like leaves, compound seed cones, wood, and pollen grains. Often conifers are generalized as “evergreens”, “pines”, or “Christmas trees” but none of those are sufficient to describe all conifers since there is no single feature which sets them apart from other plants.

Photo: Mature seed cones of Picea abies ‘Acrocona’ – RBG accession 780126*A – growing in the Pinetum of the Arboretum.

Conifers are some of the oldest (Pinus longaeva), the tallest (Sequoia sempervirens), the widest (Taxodium mucronatum), the largest (Sequoiadendron giganteum), and the rarest (Wollemia nobilis) species on the planet. They are a fascinating group of plants who are adaptable to a wide variety of locations and conditions. Although these are often conspicuous species, they are an economically important part of both the natural and cultivated landscapes throughout the world.

Photo: “General Sherman”, an impressive Sequoiadendron giganteum, grows in Sequoia National Park, California. This is amongst the oldest, tallest, and largest trees on earth with an estimated age of 2,300–2,700 years, a height of 83.8 metres (275 ft), a diameter of 7.7 m (25 ft), and is officially recognized as the largest tree by volume with an estimated bole volume of 1,487 m³ (52,513 cu ft).

Many conifers have become staples in cultivation, usually in the form of hedges, windbreaks, or screens but some gardeners include conifers in their gardens for their diversity of growth forms, textures, colours, and shapes. There are now thousands of cultivars of conifers which have been selected from wild and cultivated populations, asexually propagated, and named over the past two centuries.

Photo: Various conifers including new and historical cultivars of Juniperus, Thuja, Abies, Cupressus, Pinus, Picea, Larix, Sciaopitys, and many more provide stunning structural companions for many of the flowering plants growing throughout Rock Garden.

Although conifers are some of the most dominant plants on the planet, there are many that are just hanging on and could become extinct in our lifetimes, with one-third of all species threatened or vulnerable. Their populations are threatened by land conversion, resource exploitation, climate change, and human induced environmental changes like pollution and fire (or fire suppression).

In Ontario, we have 12 native species of conifers, with the White Spruce (Picea glauca) and Balsam Fir (Abies balsamea) being two of the most popular for holiday decorating.

Other native species to look for include the Eastern White Pine (Pinus strobus), Ontario’s provincial tree. It can live over 250 years and is known as “the Tree of Great Peace” by the Haudenosaunee First Nations of southern Ontario

Photo: The seed cones and delicate needles of the provincial tree of Ontario, Pinus strobus.

One of the longest-lived here is the Eastern White Cedar (Thuja occidentalis). It tolerates poor soils and difficult growing conditions. It can live over a thousand years even in the harsh conditions on the cliffs of the Niagara Escarpment. This is the most frequently cultivated conifer and has given rise to hundreds of diverse cultivars.

Jack Pine (Pinus banksiana) is the most northerly pine in North America and features tightly closed seed cones which can remain on the tree for many years until exposed to fire. The heat opens the resin sealed cone scales to release the seeds once fire has suppressed competing plants and provided ideal conditions for germination.

Black Spruce (Picea mariana) is transcontinental and is the most abundant species in Ontario. The seed cones can remain closed for up to 20 years until the seeds are released once exposed to fire. This is one of the most important sources of wood pulp for paper in North America.

At Royal Botanical Gardens, we feature more than 3,550 individual conifers representing 9 families, 30 genera, 136 species and over 460 unique taxa. Concentrations of conifers can be found throughout Rock Garden, in the Pinetum (a hidden gem) of the Arboretum, surrounding Laking Garden, and dispersed throughout Hendrie Park and RBG Centre. We grow conifers which are not “pines” or “Christmas trees” and we even grow conifers which are not “evergreen”, like our beloved Dawn-redwood (Metasequoia glyptostroboides), Tamarack (Larix laricina), and Bald-cypress (Taxodium distichum). Inside, you can explore conifers that are not hardy in this region within the Mediterranean Garden and the containerized collections.

Photo: This Dawn-redwood in Hendrie Park is one of the first planted in Canada. This deciduous conifer is beautiful through every season. RBG accession 52098*A – Metasequoia glyptostroboides

Conifers are one of the most exciting and diverse groups in the plant kingdom and throughout RBG. From the native and non-native species to the diverse cultivated selections, there is a conifer for every space, garden, and landscape. They add a range of colours, textures, and structures and provide the much-needed year-round interest to the garden. Visit our gardens to explore and learn more about this amazing group of plants