Conifers

Conifers are a large group of resinous, cone-bearing TREES and shrubs with 7 or 8 families, about 67 genera and over 600 species having a worldwide distribution primarily in the Northern Hemisphere. Their range is extensive, from close to the ARCTIC CIRCLE in the north and into Central America and South America. Conifers are widespread in Europe and across Asia and a few extend south into Africa. Few are tropical.

Conifers comprise the order Coniferales of the gymnosperms (nonflowering, naked seeded, woody plants). The group contains the oldest (bristlecone pines, over 4000 years old) and the tallest (Sequiodendron, interior redwood, over 100 metres tall), both of which grow in California. Conifer importance, both economically and ecologically worldwide, is far greater than their limited species diversity suggests. Exploitation, forest degradation and habitat destruction have brought about 25% of the number of species under threat of extinction.

Today 35 species of conifers are native to Canada, including Douglas fir, pine, spruce, larch, true fir, hemlock, cedar, cypress, juniper and yew. The greatest diversity of conifers occurs in the western provinces with British Columbia having 25 native species. The second greatest diversity is in the eastern and Atlantic Provinces, with relatively few species in the central provinces. The distribution of most species is limited to certain geographical regions but the distributions of 2 spruce species (black and white spruce) extend from coastal British Columbia to the Atlantic Ocean.

Anatomical Features
Leaves

Most species are evergreen, meaning that they retain their leaves throughout the year. However, a few genera, such as LARCH, are deciduous, meaning they shed all of their leaves every fall. The term evergreen does not mean that leaves are not shed, they are just not all shed each autumn. Most evergreens shed the leaves (or branches as in cedars) that were formed 2 or more years earlier so that newer branches are never bare of leaves. Most conifers have needlelike leaves as in fir, pine, spruce and larch, while others, such as cedar, cypress and juniper have scalelike leaves.

Seeds

Most conifers have seeds borne on the surface of scales, forming the seed cones, and for this reason are called gymnosperms (naked seeded plants). Seed cones also have smaller, often leaflike bracts, one positioned below each scale. They may be small and entirely hidden under the scale as in true firs or partially hidden as in hemlock or in some conifers such as Douglas fir or larch they are long and leaflike and extend beyond the scales. In these examples, the bracts are not attached to the scale. In other conifers, such as pines, the bract and scale may be partly fused forming a bract-scale complex. In still others, such as cedar and cypress, the bracts and scales are totally fused into a single structure.

Mature seed cones are commonly large and woody as in pines, spruce, larch and firs. In others, mature seed cones are small and woody as in cedar and cypress or non-woody and soft as in junipers. In a few conifers, seeds are borne singly, occasionally with a berrylike covering as in Podocarpus and yew.

Resin Ducts

Resin ducts are found in all conifers and conifer structures including roots, stems, leaves, cones and even some seeds. Resin ducts consist of tiny tubes lined with secretory cells that secrete the sticky resin (pitch) into the ducts and often to the surfaces of the tree. It serves as a protection mechanism to seal wounds or areas where leaves, cones, branches or bark have been naturally shed. Some conifers, especially pines, have been used to harvest the resin, which has several commercial uses. The earliest use was the calking for wooden sailing ships but it is still used for extraction of terpenes, a group of chemicals used for the extraction of turpentine and related oils and compounds.

Winter Strategies
During late summer and early fall, when days become shorter and temperatures decrease, temperate conifers go through several complex processes in the living tissues of leaves, stems and roots. Cell divisions and cell growth stop so there is no active growth forming new tissues or organs such as wood or leaves, respectively. Many complex chemical changes also occur, ranging from increased amounts of soluble salts and sugars and, in some, the production of anti-freeze compounds all of which increase the cold resistance of the living tissues. These complex physiological changes lower the ice-forming temperature by several degrees allowing the living tissues to survive long periods of sub-freezing temperatures.

Reproduction
All conifers have separate seed cones and pollen cones. These may be borne either on the same tree (monoecious, one home) or on different trees (dioecious, 2 homes). Pollen cones produce abundant yellow pollen, which is dispersed by wind every spring and enters the seed cones (pollination) where fertilization, embryo and seed development occur.

In most conifers pollination, fertilization, and embryo and seed development occur in one growing season, from spring through autumn. However, in the pines and a few other genera there is a delay of one year between pollination and fertilization or fertilization and seed development, and the reproductive cycle is extended over 2 growing seasons. In both types of reproductive cycles, the seed cones mature in the autumn when seed cones dry and are shed or the dry cones open or disintegrate and the seeds are shed.

Most species have seeds with either one or 2 wings that slow the fall of the seeds aiding in seed dispersal. Seeds are commonly dispersed by wind, but some are dispersed by squirrels and other rodents, and in yew and a few species of pines, dispersal is by birds. In a few conifers, entire cones are shed (abscised) rather than the individual seeds.

Families
The classification and taxonomy of conifers has changed in recent years as a result of new molecular technologies and studies of reproductive biology. There are now considered to be 7 extant (living) families and one extinct family, the Lebachiaceae. It is believed that all modern conifers evolved from the extinct Lebachiaceae during the Mesozoic Era over 200 million years ago, at about the same time as the rise of the dinosaurs. Of the 7 extant families, Araucariaceae and Podocarpaceae are oldest families distributed primarily within the southern hemisphere; Sciadopityaceae has but one genus and one species (Sciadopitys verticillata), which is native to Japan; and the 15 species (in 2 genera) of Cephalotaxaceae are all native to eastern Asia. Three families have species native to Canada.

Pinaceae

The pine family (pine, firs, spruce, larch, etc) is the largest and most familiar and widely distributed family containing 10 genera and about 220 species. Most are large trees but some species are shrubs. The Pinaceae arose soon after the Podocarpaceae and Araucariaceae but are restricted to the northern hemisphere, mostly in temperate regions, with the exception of a species native to Indonesia. However, Pinaceae species encircle the globe in the northern hemisphere and are found along ocean shores to high alpine and dry desert regions. They are very diverse and widely distributed throughout most of North America, Europe and Asia.

They all have needlelike leaves and small to large woody cones with 2 seeds per cone scale. The largest genera are Pinus (pines) with 109 species; Abies (true firs) with 49 species; and Picea (spruce) with 34 species. Other genera have fewer species including: Larix (larch) with 10 species; Tsuga (hemlocks) with 9 species; Pseudotsuga (Douglas fir) with 4 species; Cedrus (true cedars) with 4 species; and Keteleeria with 3 species.

The Pinaceae are commercially the most important conifer family in Canada. Nine species of PINE, 5 species of SPRUCE, 3 species of HEMLOCK, 3 species of larch, 3 species of true FIRS and one species of DOUGLAS FIR occur in Canada. They are most abundant in western and eastern Canada but some species of pine, larch and spruce may be found almost coast to coast.

Cupressaceae

The Cypress family (cypresses, cedars and junipers) were recently combined with the former redwood family (Taxodiaceae) because of their similarity in cone structure and reproductive development plus new molecular evidence. The current Cupressaceae family consists of 28 genera and 118 species.

They are quite variable in leaf structure. Some have deciduous needlelike leaves. Most have small scalelike leaves and a few, like the junipers and interior redwood (Sequoiadendron), have short to awl-shaped leaves. The considerable variation in leaf form (morphology) was one of the main reasons for the original separation of the 2 original families. The new classification is based on more conservative reproductive and molecular information.

The Cupressaceae may be huge trees, as shown in the redwoods, or shrubs as shown in many junipers. Mature seed cones are usually small, woody, soft or berrylike and all have completely fused bracts and scales, each of which may bear several seeds. The seeds usually have 2 small wings or no wings.

The Cupressaceae is the most widely distributed family of conifers found throughout the northern hemisphere from arctic TUNDRA to high mountains and desert areas and south into equatorial regions and then into the southern hemisphere where there they occur in South America, Africa and Australia. A few species also grow in tropical regions of Southeast Asia. Two species of CEDARS western red cedar (Thuja plicata) and eastern white cedar (T. occidentalis); one species of CYPRESS, yellow cypress (Chamaecyparis nootkatensis); and 3 species of JUNIPERS (Juniperus communis, J. horizontalis and J. virginiana) occur in Canada.

Taxaceae

The YEW family is represented by 5 genera and about 22 species. Four of the genera, including the largest and most familiar, Taxus, are distributed predominantly in the Northern Hemisphere and one genus, Austrotaxus, extends into the southern hemisphere.

The Taxaceae was previously considered to be a separate order, the Taxales, comparable to the order Coniferales because of their single-seeded berrylike seed-cone structure. But they are now included as a family within the Coniferales based on new molecular evidence showing a close genetic relationship with other conifers. Also, new reproductive evidence shows that the seed, which is enclosed by a fleshy aril, actually begins development within a reduced compound seed-cone structure. The seed-cone structure is similar to that of other conifer families, but in yew, the cone has become reduced to a single small scale and a fleshy red aril that encloses most of the seed.

The wood of Taxus is very hard and beautiful, and is used for furniture, wood carvings and archery bows. Most importantly, a chemical, taxol, can be extracted from the bark or leaves for use in medicines to treat some cancers. This chemical was synthesized in the laboratory in the early 1990s, saving Taxus species from the rapid harvest that began in the late 1980s. Two species are native to Canada: ground hemlock (T. canadensis) and western yew (T. brevifolia).

Author JOHN N. OWENS

Suggested Reading
Aljos Farjon, Conifers: World Checklist and Bibliography of Conifers (1989), A Natural History of Conifers (2008) and A Handbook of the World's Conifers (2010); John L. Farrar, Trees in Canada (1995); Robert C. Hosie, Native Trees of Canada (1979).

Links to Other Sites
Tree Canada
The website for Tree Canada. Promotes public involvement in planting and caring for trees in communities across the country. See their extensively illustrated online guide to Canadian trees.

The Plant List
Search this online database for information about one million plant species from around the world. Also, click on "major plant groups" at the bottom of the page to browse descriptions of species of interest. Fungi and algae are excluded. From the Royal Botanic Gardens, Kew, in the UK and the Missouri Botanical Garden in the US.

Flora of North America
The FNA website features information on the names, taxonomic relationships, continent-wide distributions, and morphological characteristics of all plants native and naturalized found in North America north of Mexico.

Wollemi Pine
This site describes the natural history of the Wollemi Pine (Wollemia nobilis), also referred to as the "Dinosaur tree". Discovered in Australia in 1994. From Australia's Royal Botanic Gardens & Domain Trust.

Ontario Trees & Shrubs
An illustrated searchable guide to trees and shrubs that grow in Ontario. From ontariotrees.com.

Types of Trees
Trees come in all sorts of different shapes and sizes. Find out what trees are and why healthy trees are so important to the environment. From ecokids.ca.

Field Guide: Native Trees of Manitoba
An online guide to Manitoba’s ecozones and native coniferous and deciduous trees in Manitoba. With photographs showing identifying features of various species and biological keys. A Government of Manitoba website.

Tree Book
View online book that describes tree species and ecosystems found in British Columbia. With photos and illustrations to assist species identification. From the Government of British Columbia.

Tree World
A students' guide to trees and their role in the environment. Find out about a year in the life of a tree and much more. Includes an illustrated tree guide. From the Domtar Corporation.

Native Trees of New Brunswick
Learn how to identify the native trees of New Brunswick at this website from the Canadian Forestry Association of New Brunswick.

The conifer database
A comprehensive online database about coniferous trees. Search for species by scientific name, then highlight a species listed in search results and click on the icons at the top of the table for more information.

Conifers
See an illustrated guide to conifer species from the website for the Royal Botanic Gardens, Kew.