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Classifying Conifers

Conifer needles

With so many varieties of conifer trees, have you ever wondered how people tell them apart? Understanding how the characteristics of trees affect their classification can help you identify different types. Today on the blog, we have an excerpt from Growing Conifers: The Complete Illustrated Gardening and Landscaping Guide on conifer classification. Next time you walk through a forest with conifers, see how many you can classify.

Excerpt from the Book

Classifying Conifers

Most plants are given a common name in the language where they are native, and a scientific name that is Latinized. For most people, common names are easier to remember and pronounce, but using common names can lead to confusion or be misleading. Common names contain two or more words; the last word generally denotes the genus or plant group the plant belongs to, and the first word(s) describe the plant. In some cases, however, the common name does not denote the proper plant group, such as the conifers western red-cedar or Douglas-fir. The western red-cedar is not a true cedar, and the Douglas-fir is not a true fir. To alert the reader to those instances where the conifer’s common name does not denote the correct genus, a hyphen has been added between the words of the common name.

Plants often have more than one name, even in a single region, and common names, such as cedar, are applied to many genera other than Cedrus, the true genus for cedars. To avoid this problem, botanists unambiguously give each plant a binomial (two-term) name: the genus followed by the species. The genus and species are always italicized; the genus is capitalized, and the species is lowercase. Garden conifers often have a cultivar name, which is not italicized but is capitalized and enclosed in single quotation marks. For example, in the binomial Pinus contorta var. latifolia ‘Chief Joseph’, the genus is Pinus, the species is contorta, and ‘Chief Joseph’ is the cultivar of the tree commonly known as lodgepole pine ‘Chief Joseph’. Compare how different the cultivar ‘Chief Joseph’ is from the common lodgepole pine. The common lodgepole has year-round dark-green foliage, and the ‘Chief Joseph’ has green foliage that becomes brilliant golden in autumn and winter.

Botanists often change conifer classification, and sometimes their names, as new knowledge improves our understanding of conifer genetic relationships and evolution. For this book’s purposes, we will use the current classifications and the more-obvious physical traits that you can use to identify conifers in your yard and community. The following section gives you the main identifying characteristics to use in identifying conifers.

Leaves

Shape

  • Narrow needle-shaped leaves, as in the pines (genus Pinus).
  • Flattened blades, as in redwood (Sequoia), yew (Taxus), and hemlock (Tsuga).
  • Flat scale-like leaves, as in the genera false-cypress (Chamaecyparis), arborvitae (Thuja), and true cypress (Cupressus).
  • Awl-shaped leaves tapering to a slender, stiff point, as in the juvenile foliage of many junipers (Juniperus).
  • Flat strap-like leaves, as in plum-pines (Podocarpus), which also have other common names.

Flat, scale-like leaves in false-cypress (Chamaecyparis obtusa) (left), and in arborvitae (Thuja plicata) (right).

Cross-section: For example, spruce (Picea) needles have a quadrangular cross-section, and firs have a flat cross-section.

Attachment: Where the leaves attach to stems, twigs, and branchlets (small branches or divisions of small branches, especially terminal divisions; the term is usually applied to branches of current or preceding year):

  • Needles fastened in tight bundles at the base by a sheath, or fascicle, as in pines.
  • Needle clusters radiating out from a peg-like bud without a basal sheath, as on the short shoots of larch (Larix) and true cedar (Cedrus).
  • Single needles spread along the branch from a peg-like stalk, as in spruce (Picea).
  • Single needles attached directly to the twigs and branchlets, as in true fir (Abies), Douglas-fir (Pseudotsuga menziesii), and hemlock (Tsuga).

Needles attached directly to the stem in the Min fir Abies recurvata var. ernestii.

Arrangement:

  • Opposite, as in dawn redwood (Metasequoia glyptostroboides).
  • Alternate, as in bald-cypress (Taxodium distichum).
  • Spiral, as in true firs and Douglas-fir, but twisted at the base to appear two-ranked.
  • Whorled, as in juniper.
  • Spiral, as in Japanese-cedar (Cryptomeria) and giant sequoia (Sequoiadendron).

The spiral needles of Douglas-fir are twisted at their base and therefore appear two-ranked.

Number in a cluster:

  • Two, three, or five needles per cluster, as in pine.
  • Greater than five, as in larch or cedar.
  • Markings: White bands caused by a waxy coating, or white bloom, around the tiny stomata.
  • Two white stomata bands on the lower surface, as in grand fir (Abies grandis), Pacific silver fir, and western hemlock.
  • Two stomata bands evident on the lower surface and one on the upper surface, as in subalpine fir (Abies lasiocarpa).
  • Two stomata bands evident on the upper and lower surface, as in noble fir.
  • No distinct stomata bands, as in yew.
  • On lower surface, in the shape of a butterfly, as in western red-cedar.
  • On lower surface, in the shape of an “x,” as in Port Orford-cedar.

Pine needles have two, three, or five in a cluster.

Timespan: Deciduous conifers, such as species of larch at high altitudes or in subalpine regions, retain their leaves for as little as five months. Other deciduous conifers, including Taxodium, Metasequoia, and Pseudolarix, retain their leaves from spring to fall. Most evergreen conifers retain their leaves for two to six years before dropping them. However, some evergreen conifers are exceptions to this rule. The Pacific silver fir retains its foliage for up to 22 years, and the Great Basin bristlecone pine (Pinus longaeva) and some Araucaria species can retain their leaves for up to 50 years. Because evergreen conifers lose a small proportion of their leaves annually, they don’t need to produce a complete set of leaves each year, helping them succeed on nutrient-limited soils. The oldest interior needles on most evergreen conifers—such as those of pine, spruce, fir, and arborvitae—turn yellow or brown and drop off in the fall, while the remaining leaves at the tips of the branches stay green. The change in needle color and needle drop is a normal physiological response to cooler nights and shorter days. In contrast, some needles on evergreen yews turn yellow and drop in late spring and early summer, when the temperature warms. Old interior needles can also shed because of damage by pests, such as spider mites, which cause yellowish spots or stippling; pathogenic fungi, such as Rhizosphaera needle cast disease; or environmental factors, such as drought and nutrient deficiency.

Fragrance: Many conifers have a distinctive scent when the foliage is crushed.

Branching

  • Conifers with whorled branches that form a circular pattern around the central leader or central portion of the tree, such as pines, spruces, true firs, true cedars, and Douglas-firs, have one growth spurt each spring at branch tips and the top of the central leader, from buds formed the previous year. These conifers don’t have latent buds on old wood.
  • Conifers with a random branching habit, including arborvitae, false-cypress, yew, juniper, and hemlock, have multiple growth spurts throughout the growing season and have many latent buds along their stems.

There are many other ways to classify trees that are discussed in Growing Conifers. This book is an essential, comprehensive resource for gardeners and landscape professionals looking to develop beautiful, sustainable landscapes.

About the Author

Author John J. Albers

John J. Albers is an educator for the Washington State Nursery and Landscape Association, a certified sustainable landscape professional, a former Master Gardener, and the creator of Albers Vista Gardens, which contains 1,200 different plants. Author of The Northwest Garden Manifesto, he lives in Bremerton, Washington.

About the Photographer

Photographer David E. Perry

Author David E Perry

David E. Perry is a professional photographer who has photographed for books, including The Northwest Garden Manifesto, magazines, Fortune 500 reports, and national ad campaigns for over 35 years. He lives in Seattle, Washington.

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