Two conifers turn up in almost every biology course, and students often assume they are the same kind of tree. They are not. Pinus is the pine genus, and Thuja is a genus of scale-leaved evergreens.
Both are gymnosperms, so both bear cones instead of flowers and both keep their seeds in the open. Everything after that differs. This guide compares the two genera, shows how to tell them apart in the field, and explains why the word cedar causes so much confusion.
Two Genera, Two Families
Pines and Cypresses Are Not Close Cousins
Pinus belongs to the family Pinaceae, the pine family. Thuja belongs to Cupressaceae, the cypress family. The two sit in the same broad group of conifers, but they are not the same genus or the same family.
That matters for identification. A Thuja is not a pine, and treating the two as interchangeable will lead you to the wrong name for both.
Common Names Are the Problem
True cedars are species of the genus Cedrus, which sits in Pinaceae. The trouble is that many unrelated conifers also carry cedar in their common names.
Thuja plicata is called western redcedar, yet it is a Thuja, not a Cedrus. Thuja occidentalis is known as arborvitae, eastern white-cedar, or northern white-cedar. Field guides live with these names, but they are habits of speech rather than statements about relationships.
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| Eastern white pine needles. They grow in a bundle rather than singly along the twig, which is the pine signature. Image: Chris Light, CC BY-SA 4.0, via Wikimedia Commons |
Pinus: Needles in Bundles
Fascicles and Their Sheaths
Pine needles grow in clusters called fascicles. A sheath wraps the base of each bundle, and in some species the sheath falls away as the needles age.
The number of needles per bundle varies by species. Scots pine carries two, ponderosa pine carries three, and eastern white pine carries five. Do not turn those three numbers into a rule. The genus covers a wider range, and there are exceptions on both sides.
Cone Timings and Resin
Pines are monoecious, which means one tree carries both pollen cones and seed cones. On an eastern white pine the smaller male cones tend to sit lower in the crown, with the female cones higher up.
A pine seed cone is a slow project. In familiar temperate pines it usually takes about two years to mature, and the genus range runs from roughly one and a half to three years. Scots pine cones mature about twenty months after pollination, while eastern white pine cones ripen in their second year.
Most pine seeds have a wing that helps them spin away on the wind. The pinyon pines are the exception that gets eaten: Pinus edulis produces large wingless seeds that people harvest as pine nuts.
Pines also make resin and store it in resin canals. The wood is a major timber and pulp crop, and the resin has long been collected for resin-based products such as turpentine.
Familiar pines include eastern white pine (Pinus strobus) from eastern North America and Scots pine (Pinus sylvestris) from Europe and northern Asia. Ponderosa pine (Pinus ponderosa) is widespread in the western United States.
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| A mature eastern white pine cone. It took about two growing seasons to reach this size, with the seeds sitting between the scales. Image: Keith Kanoti, Maine Forest Service, CC BY 3.0 US, via Wikimedia Commons |
Thuja: Scale Leaves and Small Cones
Five Species, Two Familiar Ones
Thuja has five living species in the usual treatment. Thuja occidentalis grows in eastern North America, Thuja plicata in western North America, and the other three in Japan, Korea and China.
Two of them are household names. Thuja occidentalis is the arborvitae sold for hedges, and Thuja plicata is western redcedar, one of the most important timber trees of the Pacific Northwest.
How the Foliage Is Built
Adult Thuja foliage is made of tiny scale-like leaves pressed close to the shoot. They sit in opposite pairs and run along the branchlet in four ranks, and the branchlets form flattened sprays that look like fans.
That is a completely different arrangement from a pine bundle. The scales are so small that the shoot itself looks like the leaf, which is why these trees read as feathery at a distance.
Cones, Seeds and Aromatic Wood
Thuja is monoecious as well, with pollen cones and seed cones on the same tree but usually on different branches.
Its seed cones are small. They carry four to six pairs of overlapping scales, mature and open within the first year, and measure roughly one centimeter across. Each seed has two narrow wings.
The foliage holds aromatic oils, and the wood of western redcedar is strongly fragrant. That fragrance, plus the wood's natural durability, made it a traditional material for shingles, siding, fences, poles and small boats.
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| Thuja plicata foliage. The leaves are scales pressed against the shoot, arranged to form flat sprays rather than bundles of needles. Image: Crusier, CC BY-SA 3.0, via Wikimedia Commons |
Telling Them Apart
The One-Second Field Check
Look at the foliage. If the leaves are needles gathered in a bundle with a sheath at the base, you are looking at a pine. If the leaves are tiny scales lying flat along a shoot that forms fans, you are looking at a Thuja.
Cone shape adds a second clue. Pine cones are larger and their scales are stiff and woody, and they take more than a year to ripen. Thuja cones are small, thin-scaled and finished in a single season.
Scale-like foliage by itself does not prove Thuja, though. Several other members of Cupressaceae wear the same kind of leaves, including junipers and false cypresses.
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| Unripe Thuja plicata cones. They are small and thin-scaled, and they finish in the same year they start. Image: S. Rae, CC BY 2.0, via Wikimedia Commons |
The Comparison, Row by Row
| Feature | Pinus (pine) | Thuja (arborvitae, redcedar) |
| Family | Pinaceae, the pine family | Cupressaceae, the cypress family |
| Leaves | Long needles grouped in fascicles | Tiny scale leaves in four ranks |
| Arrangement | Bundles with a basal sheath | Flattened sprays on the branchlet |
| Cone sexes | Both cone types on one tree | Both cone types on one tree |
| Seed cone timing | Usually about two years, range 1.5 to 3 | Within the first year |
| Seed cone size | Conspicuous, with stiff woody scales | Small, near 1 cm, thin scales |
| Seeds | Often winged; pinyon seeds are large and wingless | Two narrow lateral wings on each seed |
| Wood and aroma | Resinous; big timber and pulp crop | Fragrant oils; durable shingles and siding |
| Species count | About 110 to 130, counts vary | Five in the usual treatment |
| Familiar example | Eastern white pine, Pinus strobus | Western redcedar, Thuja plicata |
What They Share, and the Cedar Trap
Shared Gymnosperm Ground
Strip away the differences and the two genera share the basics. Neither has flowers. Both bear seeds on the scales of cones rather than inside a fruit. Both are evergreen conifers, and both build wood from tracheids.
Wind carries pine pollen, as it does for most conifers, so neither tree needs an insect to reproduce. That is a quiet advantage in a cold climate with few active pollinators.
Why Cedar Names Mislead
The cedar confusion is worth learning early, because it repeats across the conifers. Eastern redcedar is a juniper. Port-Orford cedar is a false cypress. Incense cedar is a Calocedrus.
None of those three is a true cedar either, and the same goes for western redcedar. Real cedars belong to Cedrus. When a common name and a genus name disagree, the scientific name is the one that settles it.
Key Terms in Plain English
| Term | What it means here |
| Pinus | The pine genus, in the family Pinaceae. |
| Thuja | A genus of scale-leaved evergreens in Cupressaceae. |
| Pinaceae | The pine family, which also holds firs, spruces and cedars. |
| Cupressaceae | The cypress family, which holds Thuja and junipers. |
| Fascicle | A bundle of pine needles with a sheath at the base. |
| Scale leaf | A tiny leaf pressed against the shoot, as in Thuja. |
| Monoecious | Bearing male and female cones on the same plant. |
| Pollen cone | The male cone, which releases pollen. |
| Seed cone | The female cone, which carries the ovules and seeds. |
| Tracheid | A long water-carrying wood cell typical of conifers. |
| Resin canal | A passage in pine wood and bark that carries resin. |
| Arborvitae | A common name for Thuja occidentalis. |
| Western redcedar | The common name for Thuja plicata. |
| Cedrus | The genus of the true cedars. |
| Serotinous cone | A cone that stays closed until heat opens it; not all pines. |
| Pinyon | A group of pines with large, edible, wingless seeds. |
Key Takeaways
- Pinus is in Pinaceae and Thuja is in Cupressaceae; a Thuja is not a pine.
- Pine needles grow in fascicles, or bundles, with a sheath at the base.
- Thuja leaves are tiny scales pressed to the shoot in four ranks.
- Pine seed cones usually need about two years; Thuja cones finish in one.
- Both genera are monoecious, with pollen and seed cones on the same tree.
- Names like western redcedar are common names, not signs of true cedar kinship.
Frequently Asked Questions
Is a Thuja a kind of pine?
No. Pinus is in Pinaceae and Thuja is in Cupressaceae. They are both conifers, but they are different genera in different families.
Is western redcedar a true cedar?
No. True cedars belong to the genus Cedrus. Western redcedar is Thuja plicata, a member of the cypress family.
Do all conifers have needle leaves?
No. Pines have needles, but Thuja and many other Cupressaceae have scale-like leaves instead.
Why do pine cones take so long to mature?
A pine seed cone develops through more than one growing season, usually about two years, while a Thuja cone ripens and opens within a single year.
Key references
• Gymnosperm Database: Pinus
• Gymnosperm Database: Thuja
• USDA Forest Service: Eastern white pine
• USDA Forest Service: Western redcedar
• Gymnosperm Database: Thuja plicata
• Duke Gardens: True cedars and cedar confusion
Images: Wikimedia Commons, with the author and license named in each caption. This article is general science education.
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