Chamaecyparis thyoides (Atlantic white-cedar) description

Conservation Status

(both subsp.)

Chamaecyparis thyoides

(L.) Britton, Sterns & Poggenb. (1888)

Common names

Atlantic white-cedar, southern white-cedar (Michener 1993), white cypress (Dallimore et al. 1967), swamp cedar.

Taxonomic notes

Two subspecies:

Chamaecyparis thyoides subsp. henryae (H.L.Li) A.E.Murray. Syn. C. henryae H.L.Li (1962), C. thyoides var. henryae (H.L.Li) Little, Cupressus thyoides subsp. henryae Silba.
Chamaecyparis thyoides subsp. thyoides. Syn. Cupressus thyoides L. and 27 other obsolete synonyms; see POWO for the full list.

You will sometimes see subsp. henryae treated at varietal rank but as it has a distinct distribution, morphology, and ecological associations, it clearly warrants subspecies rank. Based on morphology, Li (1962) proposed a relationship to Callitropsis nootkatensis (which at the time was generally assigned to Chamaecyparis) rather than to Ch. thyoides, but fossil evidence and molecular taxonomy have not supported that idea. Chloroplast markers place C. thyoides sister to C. formosensis and C. pisifera, which is likely a result of incomplete lineage sorting in late Cretaceous time (Wang et al. 2003, 2022). Both fossil and molecular evidence indicate Chamaecyparis was widespread in the late Cretaceous, but the K-Pg mass extinction eliminated all taxa except the C. thyoides ancestor and the most recent common ancestor of all the other extant species. Nuclear DNA gives similar evidence, placing C. thyoides sister to all other species of Chamaecyparis, with a most recent common ancestor in the late Cretaceous (Wang et al. 2022).

Description

Trees to 40 m tall and 200 cm dbh, typically with a single trunk and a conical crown of ascending branches that with age becomes broad and open. Bark flaky, with age becoming thick (to 5 cm), deeply fissured, reddish brown weathering to gray-brown, exfoliating in long strips. Foliar units deciduous after 4-5 years. Leaves scale-like, decussate, imbricate, decurrent, coriaceous, 1.5-2.5 × 1-1.5 mm on terminal twigs but up to 10 mm long on leading shoots, dimorphic but facial leaves only slightly shorter than laterals, rhombic to oblong, sometimes keeled, obtuse to acuminate, with or without a central raised abaxial gland, laterals with an incurved apex, margins entire, stomata on both surfaces but inconspicuous, mostly at leaf base and margins; yellow-green to gray-green. Pollen cones terminal, numerous, solitary, ovoid, 1.5-3 × 1-2 mm, yellowish turning light to dark brown, with 8-12 subcordate microsporophylls and 2(-3) large yellow pollen sacs. Seed cones terminal, solitary, maturing in 1 year, subglobose, 4-7 mm diameter when opened, glaucous purple ripening brown, usually with 6 opposite pairs of bract-scale complexes, peltate, irregularly angular, up to 3-5 mm wide, surface depressed and rugose with a curved spiny umbo; 2 seeds at the base of each scale, usually 8-12 developing in each cone, each seed 2-2.5 mm across, slightly flattened, ovoid, shallowly grooved, dark brown, surrounded by 2 lateral wings ca. 1 mm wide (Farjon 2010). See García Esteban et al. (2004) for a detailed characterization of the wood anatomy.

Subsp. thyoides has conspicuously glandular scale leaves, especially the facials, and these are not keeled. The pollen cones mature very dark brown. Subsp. henryae has nonglandular or inconspicuously glandular facial leaves, which are often distinctly keeled; the pollen cones mature light brown (Farjon 2010). Subsp. henryae also has smoother bark, less flattened branchlets, lighter yellowish green foliage, a steeper angle of leaf appression to the stem, and slightly larger cones, seeds, and seed wings (Li 1962), and it has more open growth with less congested foliar units; it also can potentially become a larger tree (M.P. Frankis pers. obs. 1999.02.03).

Distribution and Ecology

The subspecies have disjunct ranges within the United States. Subsp. thyoides occurs on the Atlantic Coastal Plain in Maine, New Hampshire, Massachusetts, Rhode Island, Connecticut, New York, New Jersey, Delaware, Pennsylvania, Maryland, Virginia, North Carolina, South Carolina, and Georgia at elevations of up 0-100(-500) m, chiefly in bogs and swamps. Precipitation is 1020-1630 mm, distributed throughout the year. Temperatures vary widely, with a frost-free season ranging from 140 days in the north to 305 days in the south (Little and Garrett 1990, Michener 1993). Soils tend to be acidic, organic or sandy, nonsaline, with prolonged inundation. C. thyoides mainly occurs in isolated, fairly pure stands within a matrix of the regionally dominant forest type, which varies widely across the latitudinal range of the subspecies but is usually dominated by deciduous hardwood trees with some Pinus spp. and, in the south, Taxodium distichum (Farjon 2010). Besides occurring in pure stands, it is also associated with Acer rubrum, Nyssa sylvatica, Betula alleghaniensis, Pinus strobus, Betula populifolia, Pinus serotina, Tsuga canadensis, and Gordonia lasianthus. It is an early-successional species, having lower shade tolerance than common associated angiosperms such as Acer rubrum and Nyssa sylvatica (Little and Garrett 1990).

Distribution data from USGS (1999). Subsp. thyoides shown in red, subsp. henryi in purple. Points plotted as tree icons represent isolated or approximate locations.

In New Jersey, pollen is shed in April and seed is dispersed in October-November; timing may be expected to vary by latitude. Specimens as young as 3 years have been observed to bear seed cones. Cone production is greatest in mature, open-grown, forest dominant trees, which typically produce substantial seed crops every year, commonly producing about 20 million seeds/ha (seed weigh about 1 mg). The seed floats and is presumably dispersed primarily by wind and by water transport. Seeds may remain viable for years after seedfall, and will germinate readily at 16% of full sunlight, so germination will occur under a forest canopy. Seedling taproots are very short, so any moisture stress is likely to be lethal. Microrelief seems to greatly influence successful establishment, with inundated areas and elevated hummocks having no establishment due to flooding or drought stress, respectively. Under optimal conditions seedlings can grow 0.3 m/year for 50 years, while a suppressed seedling may show as little as 1 cm/year growth. Vegetative reproduction through layering or basal sprouting can occur, and is commonly seen in response to herbivory by rodents and deer (Little and Garrett 1990).

Most stands have regenerated after severe disturbance, typically, severe fire or windthrow. Windthrow often seems to be associated with hurricanes, and the accompanying storm surge can also kill the forest due to salt water exposure. These highly destructive disturbances can be followed by regeneration of a pure Chamaecyparis stand derived from the soil seed-bank. Alternatively, if other species are also residual from the disturbance, then a mixed stand may regenerate (Little and Garrett 1990). Fire can be remarkably destructive if it also results in combustion of the peat substrate, causing the site to be converted to unsuitable habitat (New Jersey Forest Service 2020).

As for pests and pathogens, there are no insect pests of concern. There are many fungal associates, some harmful, some innocuous, some beneficial. The pathogens include Keithia chamaecyparissi and Lophodermium juniperinum, which attack white-cedar foliage; Gymnosporangium ellisii, which causes a broom-like development of branches; G. biseptatum, which occasionally causes a spindle-shaped swelling of stems or branches; Armillaria mellea, Heterobasidion annosum, and Phaeolus schweinitzii, which are root rots; and the heartwood rot Fomitopsis cajanderi, although the heartwood is very resistant to decay (Little and Garrett 1990). Innocuous or potentially beneficial fungi include a large number of foliar endophytes; at least 88 species are known, typically with 10 different taxa present in a tree; the most common of these are Nodulisporium sp. and Mycoleptodiscus atromaculans (Bills and Polishook 1992). Beneficial fungi are primarily vesicular-arbuscular mycorrhizae (Cantelmo and Ehrenfeld 1999).

Although C. thyoides was heavily exploited for timber during the 18th-20th centuries and large or old trees are now quite rare, both subspecies remain common and widespread, and are of "Least Concern" for conservation (Farjon 2013). However, of the 16 states that comprise its range, the species is now considered vulnerable in 6 (AL, DE, MD, NC, NH, VA), imperiled in 4 (GA, ME, MS, NY), and presumed extirpated in Pennsylvania. "It has declined since European settlement, as a result of drainage, conversion to drained farmland, logging, and incompatible forest management practices. Threats include development, logging and incompatible forest management, lack of fire, and invasive exotic plants, such as Chinese tallow-tree (Triadica sebifera)" (NatureServe 2025). Climate change, specifically sea level rise, has also been implicated as a factor of decline, converting cedar swamps to salt marsh (New Jersey Forest Service 2020).

Subsp. henryae occurs in Florida, Alabama and Mississippi at elevations up to 100 m in bogs and swamps of the Gulf Coastal Plain (USGS 1999). It experiences a warmer, wetter climate than subsp. thyoides, with about 1680 mm annual precipitation with a June-August maximum, an average January minimum temperature of 3.6°C, and an average July maximum of 32.4°C; vapor pressure deficits peak in June at 22.7 hPa, which is typical for mesic areas of the eastern U.S. (PRISM Climate Group 2025). Its ecology is generally similar to subsp. thyoides but it is mostly a larger tree with a primarily riparian distribution along low-lying sandy rivers, commonly in areas adjoined by upland forest dominated by native pines such as Pinus elliottii, P. palustris, and P. taeda; the usual substrate is sand, though occurrences on organic muck are also reported (Li 1962 and field observations in 2024).

Remarkable Specimens

The official "champion" tree, as measured in 2019, is 166 cm dbh and 19.2 m tall with a crown spread of 8.5 m; it grows in Muskingum County, Ohio, which means it is an ornamental specimen. Comparable in size is the largest recorded specimen of subsp. henryae, 150 cm dbh and 27 m tall with a 13.0 m crown spread, located in Brewton, Alabama (American Forests 1996). This is an older record and I don't know if this specimen survives. In 2024 I found one in Florida that was 106.4 cm dbh and 13.3 m tall. Trees up to 37 m tall have historically been recorded in Virginia and/or North Carolina (Little and Garrett 1990). Much larger specimens were recorded historically. Cook (1868) reported, based on interviews with local people, that "The average size of the old trees was from two to three feet in diameter; those of four, five, and six, and even seven feet, were found, but rarely." Seven feet is 213 cm.

The oldest crossdated living specimen, 254 years, is documented in a tree-ring chronology covering the period 1841-2016, collected at the Acushnet cedar swamp, Massachusetts by Jessie Pearl and colleagues (doi.org/10.25921/bx4r-gy67). The 254-year lifespan was shown in one living tree. The chronology was used in at least one paleoclimate study (Pearl et al. 2020). The greatest age that has been reliably attested comes from Cook (1868): "The swamps are now cut off when the timber is of about sixty years' growth. Formerly, trees of great age were found. Mr. Charles Ludlam counted seven hundred rings of annual growth in a tree which was alive when cut down. Dr. Beesley counted ten hundred and eighty in a stump; and Hon. J. Diverty found one thousand in a log dug up out of the swamp earth." Later he reports "Dr. Beesley, of Dennisville, some years since communicated to the newspapers an article on the age of the cedar swamps, in which Dr. B. says that he counted 1,080 rings of annual growth between the centre and outside of a large stump six feet in diameter."

Ethnobotany

Little aboriginal use of the species has been recorded. The South Ojibwa people used a decoction of the leaves as a herbal steam source for treating headache and backache, and a poultice of crushed leaves and bark would be applied for headache (Native American Ethnobotany DB 2025).

Historically and down to the present (2025), the species was harvested extensively for its wood; in southern New Jersey, for example, it has been the most valuable tree since the 17th century (New Jersey Forest Service 2020). Harvest of living stands and conversion of its wetland habitat have virtually eliminated all living large and old trees and extirpated the species in many areas, but the tree is still grown in managed plantations as a timber source, where it can typically be harvested in 60-70 year rotations. Little and Garrett (1990) explain "The lightweight, straight-grained wood of Atlantic white-cedar is easily worked, resistant to decay, and shrinks and warps very little during seasoning. These characteristics probably govern its use today as much as they did in colonial times. In those times it was used for shingles, barrels, tanks, and small boats. Today it is still used where durability, light weight, and resistance to weathering are important considerations: telephone poles, piling, ties, siding, boat railing, and ice cream tubs."

The species has also found use as an ornamental conifer. Subsp. thyoides is hardy to Zone 5 (cold hardiness limit between -28.8°C and -23.3°C) and subsp. henryae to Zone 8 (Bannister and Neuner 2001). A. J. Rehder (1949) listed 30 published cultivars (Michener 1993), and the number has likely increased. It has also been used in dendrochronology; an absolutely dated 2500 year-long tree ring record has been assembled from living, archaeological, and subfossil C. thyoides found at varied sites in the northern half of its range (Pearl et al. 2019).

With regard to that subfossil wood, this is another species, like Agathis australis and Taxodium distichum, where the recovery of subfossil wood preserved in wetlands has amounted to a substantial industry. Today that industry appears to have disappeared, but Cook (1868) provided the following description based on observations he made in southern New Jersey; also see the drawing at right, from his account, showing the distribution of subfossil cedar.

White cedar logs of the common species are found fossil, in abundance in salt-marshes, in Cumberland and Cape May Counties. ... At several places in southern New Jersey, an enormous anount of white cedar tlmber is found buried in the salt marshes, sound and fit for use, and a considerable business is carried on in mining this timber and splitting it into shingles for market.

Mr. Charles Ludlam told me that he recently found a log in the swamps which, from its cut ends, he was satisfied had lain there ever since the timber was last cut off, which was sixty years ago. It was about a foot in diameter, and the accummulation of matter on the surface since that time was enough to entirely bury it. Timber which is buried in the swamp undergoes scarcely any change; trees which are found several feet under the surface, and which must have lain there for hundreds of years, are as sound as ever they were; and it would seem as if most of the timber which had ever grown in these swamps was still preserved in them. Trunks of trees are found buried at all depths beneath the surface, quite down to the gravel; and so thick, that in many places a number of trials will have to be made before a sounding-rod can be thrust down without striking against them. Tree after tree, from two hundred to one thousand years old, may be found lying crossed one under the other in every imaginable direction. Some of them are partly decayed, as if they had died and remained standing for a long time, and then been broken down. Others have been blown down, and their upturned roots are still to be seen. Some which have been blown down, have continued to grow for a long time afterwards, as is known by the heart being very much above the centre, and by the wood on the under side being hard and boxy. These trunks are found lying in every direction, as if they had fallen at different times, as trees would in a forest now.

The cedar logs which are buried in the swamps are mined, or raised and split into shingles; and this singular branch of industry furnishes profitable occupation to a considerable number of men. In conducting this latter business a great deal of skill and experience is requisite. As many of the trees were partly decayed and worthless when they fell, it becomes important to judge of the value of the timber before much labor is wasted upon it. With an iron rod the shingler sounds the swamp until he finds what he judges to be a good log; he tries its length and size with this rod; with a sharp-cutting spade he digs through the roots and down to it; he next manages to get a chip from it, by the smell of which he can tell whether it was a windfall or a breakdown, that is whether it was blown down or broken off. The former are the best, as they were probably sound when they fell. If he judges it worth working, he cuts out the matted roots and earth from over it, and saws it off at the ends. This latter operation is easily performed, as the mud is very soft and without any grit. By means of levers he then loosens it, when it at once rises and floats in the water, which is always very near the level of the swamp. The log is then cut into shingle lengths, and split into shingles. The logs are sometimes, though rarely, worked for thirty feet. It is very interesting to see one of these logs raised. It comes up with as much buoyancy as a freshly fallen cedar; not belng water-logged at all. The bark on the under side looks fresh, as if it had lain but a few days; and what is remarkable, the under side of the log is always the lightest; the workmen observe that when the logs floats in the water it always turns over, the side which was down coming uppermost.

Cook also observes that "when the cedar grows so that its roots can reach hard ground, as they can when the swamp is shallow, that then the timber is worthless on account of the fibres interlocking so that it cannot be split into shingles."

Observations

Blackwater River State Park in Florida has abundant trees of subsp. henryae growing along the river and easily accessed by a good trail system. The park also has the largest known specimen in Florida.

Wellfleet, MA has an Atlantic White Cedar Swamp interpretive trail.

Apart from these, I know of no especially good locations, but iNaturalist shows a large number of sites where the species can be found on public lands. I suspect a small boat is frequently useful.

Remarks

The epithet thyoides indicates a similarity to Tetraclinis, using its classical Greek name. The epithet henryae honors the collector, Mary G. Henry (Li 1962).

Citations

American Forests 1996. The 1996-1997 National Register of Big Trees. Washington, DC: American Forests.

Bills, G. F. and J. D. Polishook. 1992. Recovery of endophytic fungi from Chamaecyparis thyoides. Sydowia 44(1):1-12.

Cook, G. H. 1868. Geology of New Jersey. New Jersey Geological Survey. 900 p. Available: New Jersey Dept. of Environmental Protection, accessed 2025.03.03.

Farjon, Aljos. 2013. Chamaecyparis thyoides. The IUCN Red List of Threatened Species 2013: e.T42214A2962150. https://dx.doi.org/10.2305/IUCN.UK.2013-1.RLTS.T42214A2962150.en, accessed 2025.03.03.

Li, Hui-Lin. 1962. A new species of Chameaecyparis. Morris Arboretum Bulletin 13:43. Available: Biodiversity Heritage Library, accessed 2025.02.24.

Little, S. and P. W. Garrett. 1990. Chamaecyparis thyoides (L.) B.S. P. Atlantic White-Cedar. Pp. 103-108 in Burns, R.M. and B.H. Honkala (eds.), Silvics of North America, Vol. 1, Conifers. Washington DC: USDA Forest Service Agriculture Handbook 654. Available: https://www.srs.fs.usda.gov/pubs/misc/ag_654/volume_1/chamaecyparis/thyoides.htm, accessed 2025.03.03.

Native American Ethnobotany DB. 2025. Cupressaceae Chamaecyparis thyoides (L.) B.S.P. http://naeb.brit.org/uses/species/861/, accessed 2025.03.03.

NatureServe. 2025. Chamaecyparis thyoides. https://explorer.natureserve.org/Taxon/ELEMENT_GLOBAL.2.139336/Chamaecyparis_thyoides, accessed 2025.03.03.

New Jersey Forest Service. 2020. Atlantic White Cedar Wetland Ecosystem Restoration Strategy. State of New Jersey Department of Environmental Protection. Available: https://www.nj.gov/dep/parksandforests/forest/atlanticwhitecedar/docs/2020-09-25_AWCstrategy-final.pdf, accessed 2025.03.03.

Pearl, Jessie K., Kevin J. Anchukaitis, Neil Pederson, and Jeffrey P. Donnelly. 2020. Multivariate climate field reconstructions using tree rings for the northeastern United States. Journal of Geophysical Research: Atmospheres 125(1), e2019JD031619. doi.org/10.1029/2019JD031619.

PRISM Climate Group. 2025. 30-Year Normals (1991-2020) for 30.8961°N, 87.6238° W. https://prism.oregonstate.edu/normals/, accessed 2025.03.03.

Wang, W. P., Hwang, C. Y., Lin, T. P., and Hwang, S. Y. 2003. Historical biogeography and phylogenetic relationships of the genus Chamaecyparis (Cupressaceae) inferred from chloroplast DNA polymorphism. Plant Systematics and Evolution 241(1):13–28. https://doi.org/10.1007/s00606-003-0031-0.

Wang, Y., Ruhsam, M., Milne, R., et al. 2022. Incomplete lineage sorting and local extinction shaped the complex evolutionary history of the Paleogene relict conifer genus, Chamaecyparis (Cupressaceae). Molecular Phylogenetics and Evolution 172:107485. https://doi.org/10.1016/j.ympev.2022.107485.