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Edwin & Frances Hunter Arboretum Images 4: Conifers #1

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Araucaria Family (Araucariaceae)

The araucaria family (Araucariaceae) includes some of the most remarkable conifers on earth. They are tall trees native to forested regions of South America and Australia. In majestic size and beauty, they certainly rival the coniferous forests of North America and Eurasia. In fact, they are considered the southern counterpart of our northern pine forests. Fossil evidence indicates that ancestral araucaria forests date back to the age of dinosaurs. In fact, the magnificant trees of Petrified Forest National Park in Arizona came from ancient forests of this plant family that lived more than 200 million years ago. It has been suggested that Baltic amber and the European gemstone called jet originated from ancient araucarian forests, but there is also evidence that other conifer families may have been involved in the formation of these vast deposits.

The Araucariaceae contains three remarkable genera of cone-bearing trees: Araucaria, Agathis and Wollemia. The type genus Araucaria is derived from "Arauco," a region in central Chile where the Araucani Indians live. This is also the land of the "monkey puzzle" tree (A. araucana), so named because the prickly, tangled branches would be difficult for a monkey to climb. Fossil evidence indicates that ancestral araucaria forests resembling the present-day monkey puzzle date back to the age of dinosaurs. In fact, it has been suggested that the tree's armor of daggerlike leaves was designed to discourage enormous South American herbivorous dinosaurs, such as Argentinosaurus weighing an estimated 80 to 100 tons! Another ancient South American species called pino paraná or paraná pine (A. angustifolia) grows in southern Brazil and Argentina. Three species of Arucaria are shown in the image to the right.

A South American monkey puzzle tree (Araucaria araucana). The prickly, tangled branches would probably be difficult (and painful) for a monkey to climb. Fossil evidence indicates that ancestral araucaria forests resembling the present-day monkey puzzle date back to the age of dinosaurs.

Close-up view of the dense, sharp-pointed leaves of the monkey puzzle tree (Araucaria araucana). This species does not grow well in southern California, but forms beautiful specimen trees in the Pacific northwest and England. An ancestral species formed extensive forests in Europe during the Jurassic Period, about 150 million years ago.

Left: The Australian Bunya-Bunya tree (Arauacaria bidwillii). Right: Cook Pine (A. columnaris) or possibly a hybrid with the Norfolk Island pine (A. heterophylla). The Cook Pine is naturalized throughout the Hawaiian Islands and has a slender, spirelike crown. The name A. excelsa has been used incorrectly for the Cook Pine and Norfolk Island pine.

There appears to be some disagreement whether we have both Norfolk Island and Cook pines in southern California. In fact, many older references list only the Norfolk Island pine. The Norfolk Island pine typically has well-spaced, tiered, horizontal limbs and a distinctive silouette that is easy to spot from a distance; however, there are also trees with more closely-spaced limbs and a columnar, slender crown resembling the Cook pine. According to Trees of Hawaii by Angela Kepler (1990), most of the trees called Norfolk Island pine in Hawaii are actually Cook pines. They are naturalized throughout the Hawaiian Islands and have been exported as container-grown "Christmas trees" to the U.S. mainland. So it looks like some our southern California Norfolk Island pines are actually Cook pines, particularly if they were imported from Hawaii.

Cook and Norfolk Island Pines in the Palomar College Arboretum

Norfolk Island Pine (Araucaria heterophylla)

Norfolk Island Pine (Araucaria heterophylla)

The Norfolk Island pine (Araucaria heterophylla) has a distinctive profile with characteristic spacing between the horizontal branches. Bark of the Norfolk Island pine typically peels into slender rolls, unlike bark of the Cook pine that exfoliates into larger flakes.

In general, the interval between tiers of limbs is greater on the Norfolk Island pine, particularly on younger trees. In addition, the horizonal limbs are longer than those of the Cook pine. The Cook pine has a slender, spire-like crown with shorter, more closely-spaced horizontal branches. Throughout southern California, there are trees with branching intermediate between the two previous species. The leaf shape and size is variable and not very useful in separating these two species. Some authors have suggested that the bark of cook pine exfoliates into larger flakes. This appears to hold true in the Palomar College Arboretum; however, I have seen trees with intermediate bark flakes. In fact, trees in southern California with intermediate characteristics between the two species may be hybrids.

Cook pines (Araucaria columnaris) in Encinitas, California

Strikingly Different Cook & Norfolk Island Pines in San Marcos

Left: Cook pine (Araucaria columnaris). Right: Norfolk island pine (A. heterophylla). Photo taken in residential neighborhood west of Palomar College. Note Owens Peak (Palomar "P" Mountain) in the distance. It would be difficult to classify these as the same species.

The Leaning Of Cook Pines (Araucaria columnaris)
Cook pines (Araucaria columnaris) in the northern hemisphere exhibit the peculiar habit of leaning in a southerly direction. In the southern hemisphere the trees commonly lean in a northerly direction. Matt Ritter of California Polytechnic State University, San Luis Obispo and a team of coauthors including Jason W. Johns , Jennifer M. Yost , Dean Nicolle and Boris Igic published an article in Ecology Volume 98 (September 2017) entitled "Worldwide Hemisphere-Dependent Lean In Cook Pines." They studied 256 Cook pines scattered across five continents and collected tree data at 18 locations between latitudes of 7°- 35°north, and 12°- 42°south. The median lean for all trees measured is 2.42 m away from the base, and the median tree height is 18 m, resulting in an 8.05° lean angle. The Leaning Tower of Pisa has a lean angle of 3.99 degrees. Unlike other species of Araucaria, and other conifers in general, their data showed that Cook pines in both hemispheres lean toward the equator. The Ritter team offered several plausible hypotheses for this unusual leaning habit.

Cook pines originally come from New Caledonia, a tropical archipelago in the southwest Pacific Ocean. The trees were first classified during Captain James Cook's second voyage to circumnavigate the globe. The leaning habit in cultivated trees is so pronounced that it is often used to separate Cook pines from other similar species of Araucaria.

Plant stems exhibit positive phototropism & negative geotropism and tend to grow toward light and away from gravity, while roots exhibit positive geotropism & negative phototropism and grow toward gravity and away from light; however, there are exceptions, such as parasitic mistletoes. Non-vertical shoot growth can be caused by mechanical force from wind or snow.

Latitude appears to be a factor in the leaning of Cook pines, the further away the trees grow from the equator, the greater the slant. So possibly leaning has something to do with sunlight. Even if young trees of most species develop a tilt towards the sun, as the tree matures, it tends to correct this asymmetry and grow upwards, unless there's an environmental force preventing this, such as strong prevailing winds in one direction. But for some reason, A. columnaris trees just keep on tilting, no matter how tall they grow. And they even appear to be unique in this regard, because other Araucaria species from New Caledonia can stand up straight no matter where in the world they are planted.

According to Ritter, et al (2017), studies on the research plant Arabidopsis thaliana have identified several gene families whose regulation effects phototropic and geotropic growth; however, the mechanisms controlling the expression of these genes are not well understood, especially for woody species. The mechanisms for directional lean in A. columnaris may be related to the incidence angles of annual sunlight, gravity, magnetism, or any combination of these. Another possibility is that the lean is non-adaptive, or even harmful, and may be caused by deleterious alleles in this species.

Continued research on this fascinating conifer species may reveal some answers to these perplexing hypotheses, possibly resulting in a new scientific theory on plant growth. Stay tuned!

 J.W. Johns, J.M. Yost, D.Nicolle, B. Igic and M.K. Ritter. 2017. Ecology 98 (9): 2482-2484.

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I don't need to go far to see leaning Cook pines. In fact, on a street near my home in Twin Oaks Valley there are two excellent examples. I did not take any detailed measurements, but they are definitely leaning in a southerly direction (i.e. toward San Diego).

Phylogenetic studies comparing chloroplast DNA in the Araucariaceae show that the Norfolk Island pine's closest relatives are a clade of 13 species of Araucaria endemic to New Caledonia, including the Cook pine (A. columnaris). See: American Journal of Botany Vol. 85 ( No. 11): 1507-1516, 1998. Although New Caledonia is a relatively small island of only 19,000 square kilometers, it contains a rich conifer flora of 43 endemic species. In fact, 13 of the 19 species of Araucaria and five of the 13 species of Agathis are endemic to this island. Other rich conifer areas include New Zealand and the Sichuan Province of Western China. California is also a rich conifer region with 33 species in the pine family (Pinaceae), 2 species in the yew family (Taxaceae), 2 species in the redwood family (Taxodiaceae), and 16 species in the cypress family (Cupressaceae). In fact, 20 of the more than 100 pine species (Pinus) on earth are native to California.

According to M.G. Buck and R.H. Imoto (1982), Norfolk Island and Cook Pines were introduced to Hawaii in 1860. The two species probably hybridized and were subsequently dispersed throughout the islands. All juvenile trees today show A. columnaris traits and should probably be labeled as A. heterophylla x columnaris. The trees are propagated by seedlings, and if these are exported to the mainland, it is possible that some of our cultivated specimens are hybrids. Research forester P.G. Scowcroft (1988) states that Araucaria columnaris is the most abundant Araucaria species in the Hawaiian Islands, and that A. heterophylla is sparsely represented in Hawaii. According to Elbert L. Little, Jr. and R.G. Scolmen (1989), some exported seeds may be hybrids; however, hybridization is unlikely because the two species shed pollen six months apart. in addition, seed and foliage samples sent to Kew Gardens were all identified as A. columnaris. Dr. Little also states that seeds of A. heterophylla are larger, with a "swollen body to one cm thick." The four cotyledons on seedlings are also wider, 3 to 5 mm compared with 1.5 for A. columnaris.

  • Buck, Michael G. and Roger H. Imotos. 1982. "Growth of 11 Introduced Tree Species on Selected Forest Sites in Hawaii." Pacific Southwest Forest & Range Experiment Station Research Paper PSW-169. Forest Service, U.S. Department of Agriculture. 12p.

  • Little, E.L., Jr., and R.G. Scolmen. 1989. Common Forest Trees of Hawaii. Agriculture Handbook No. 679. Forest Service, U.S. Department of Agriculture.

  • Scowcroft, Paul G. 1988. "Germinabiliy of Cook Pine (Araucaria columnaris) Seeds under Different Storage Conditions." USDA Forest Service, Pacific Southwest Forest and Range Experiment Station, Institute of Pacific Islands Forestry, Honolulu, Hi.

The slender, spirelike crowns of Cook pine (Araucaria columnaris) form a striking contrast with the rugged mountains of Kauai, Hawaii. Cook pines are native to New Caledonia and were introduced throughout the Hawaiian islands. They are also called the New Caledonian pines.

Branchlets of three South Pacific species of Araucaria native to Norfolk Island and Australia. Although they are called "pines," they do not belong to the pine family (Pinaceae). Unlike the long, slender needles of pines, araucarian leaves are usually short, overlapping and often prickly. Top: Norfolk Island pine (A. heterophylla) with dense, overlapping, awl-shaped leaves. Middle: Hoop pine (A. cunninghamii) with flattened, needlelike leaves. Bottom: Bunya-bunya pine (A. bidwillii) with broad, sharp-pointed leaves.

Hoop pine (Araucaria cunninghamii). The bark splits horizontally at regular intervals into rings or hoops. This is the derivation of the common name "hoop pine."

Hoop pine (Araucaria cunninghamii). The bark splits horizontally at regular intervals into rings or hoops. This is the derivation of the common name "hoop pine."

Left: A Brazilian or paraná pine (Araucaria angustifolia) with A. columnaris in the distance. Right: A green branchlet of A. bidwillii (left) compared with a dried branchlet and male cones of the Brazilian pine (A. angustifolia).

Left: A cone-bearing branch from the Norfolk Island pine (Araucaria heterophylla), a close relative of the Cook pine (A. columnaris). The branches of both species are densely clothed with small, overlapping, triangular leaves. Right: A cone-bearing branch from the dammar pine or Queensland kauri (Agathis robusta), another interesting Australian member of the Araucariaceae. The leaves of this species are unusual among conifers because they are broad-leaved rather than needlelike or scalelike.

Bunya-Bunya: One Of The Largest Seed Cones Produced By A Conifer

Bunya-bunya cone (Araucaria bidwilii) compared with a pineapple.

A petrified ovulate cone of Araucaria (probably A. mirabilis) from Patagonia, Argentina. This extinct species of Araucaria dates back to the Jurassic Period (135-180 million years ago), when giant dinosaurs ruled the earth. Although prickles on the cone scales have worn away after millions of years of erosion, the cone is remarkably preserved. The right view clearly shows one seed per scale (black arrow), typical of modern-day species of Araucaria, such as the Norfolk Island Pine.

A modern representation of the phylogeny of gymnosperms based on chloroplast DNA. Dichotomous (paired) sister branches (clades) with a common ancestor are said to be monophyletic and are more closely related. For example, the conifer division Pinophyta (Coniferophyta) and ginkgo division (Ginkgophyta) have a common ancestor in the cycad division (Cycadophyta). The pine family (Pinaceae) and a sister branch leading to six additional families have a common ancestor within the division Pinophyta. In other words, the seven major families of cone-bearing trees and shrubs all evolved from the division Pinophyta. The araucaria and podocarpus families (Araucariaceae and Podocarpaceae), which have their greatest diversity in the southern hemisphere, are monophyletic and occur side-by-side on sister clades. Chart by E.M. Armstrong (2008).

  More Information & Images About The Araucaria Family  

An Insect Pest On Araucaria Trees In San Diego County

Larvae of mealybug destroyer (Cryptolaemus montrouzieri), a beetle related to ladybugs in the family Coccinellidae. This insect is used for biological control of mealybugs, such as the Araucaria mealybug (Eriococcus araucariae). Photographed on the trunk of an Araucaria tree at the San Diego Wild Animal Park.

Cypress Family (Cupressaceae)

Update On The Taxonomy Of Cypresses (Cupressus)

Just when I think I have a handle on the taxonomy of cypresses (Cupressaceae), new research emerges from the amazing field of DNA phylogeny and cladistic analysis. In October 1999, a new cypress species was discovered in northern Vietnam. It was named Xanthocyparis vietamensis. [The name Cupressus vietnamensis also appears in some garden references.] Surprisingly enough, its closest relative was found to be the Alaska cedar (Chamaecyparis nootkatensis syn. Cupressus nootkatensis), separated by thousands of miles and on opposite sides of the Pacific Ocean. The two species were so similar that the authors (Farjon et al 2002), working in Kew, England, combined them generically, and the Alaska cedar became Xanthocyparis nootkatensis. Port Orford cedar (Chamaecyparis lawsoniana) resembles other North American and Asian species of Chamaecyparis in both morphology and DNA, so its scientific name remains unchanged.

The Alaska cedar is the only Chamaecyparis species that forms spontaneous, fertile hybrids with Cupressus species when these are grown together in botanical gardens. Evidence from DNA and morphology indicates that it and the Vietnam cypress are closely related phylogenetically to the New World species of Cupressus (Little et al, 2004). The Old World species of Cupressus, however, are a separate evolutionay line, as is the large genus Juniperus. True Chamaecyparis species are only distantly related to the cluster genera that includes Old World Cupressus, Juniperus, Xanthocyparis, and New World Cupressus. In a comprehensive study, Little, D.P. (2006) proved that the Alaska Cedar and its Vietnam relative should be placed in the same genus as the New World Cupressus, but that the correct generic name for this group is Callitropsis. His study incorporated 88 morphological and wood-chemistry characteristics in 56 species of Cupressaceae, combined with sequence analysis of three chloroplast genes and two nuclear genes. The name Cupressus technically only applies to the Old World species in this genus. It turns out that Callitropsis nootkatensis was used for the Alaska cedar in 1864, long predating the name Xanthocyparis. In accordance with the Botanical Rule of Priority, the older name must be used. Therefore, Alaska cedar becomes Callitropsis nootkatensis, Vietnam cypress becomes Callitropsis vietnamensis, and the Alaska cedar-Monterey cypress hybrid becomes Callitropsis x leylandii. Damon Little (2006) also proposed that all of the New World Cupressus be placed in the genus Callitropsis. The latter genus superficially resembles the Australian genus Callitris. In the revised Jepson Manual: Vascular Plants of California, Jim Bartel changed the genus Cupressus to Hesperocyparis (western cypress). In Jim Bartel's treatment of the cypress family (Cupressaceae) in The Jepson Manual 2nd Edition (2012), the Alaska cedar is placed in the genus Callitropsis. It was moved into Xanthocyparis at the 2011 Botanical Congress in Melbourne. It is interesting to note that the Kew Index (as of 10 Nov 2017) assigns three star Convidence Levels (their highest rating) to both Cupressus and Hesperocyparis!

Based on their general morphological appearance, the New World Cupressus (Hesperocyparis) certainly resemble Old World Cupressus species; however, this similarity may be due to parallel evolution (homoplasy) in similar warm, dry climates. Just because these two groups of cypress appear similar doesn't necessarily mean that they are all closely related members of the same genus. DNA comparisons appear to reflect their true genetic affinities and differences. Groupings of species, such as Xanthocyparis, Chamaecyparis, Juniperus, Hesperocyparis and Old World Cupressus represent separate branches (clades) in computer-generated phylogenetic trees.

Using DNA to Compare Genera & Species
Homoplasy: Parallel and Convergent Evolution
  Representatives of the Taxodium Family (Taxodiaceae)  

Barcode Chloroplast Genes: matK & rbcL.  Intergenic Spacer: trnL.  Nuclear Ribosomal DNA: nrDNA

Adams, R.P., Bartel, J.A., anf R.A. Price. 2009. "A New Genus, Hesperocyparis For The Cypresses Of
      The Western Hemisphere (Cupressaceae)." Phytologia 91 (1): 160-185.

Seed cones from cypress & allies in California, Arizona and outside the U.S.

A - J: California Cypress (Hesperocyparis)
formerly placed in the genus Cupressus.
Isolated groves throughout California.
K - N: Outside California (Hesperocyparis)
formerly placed in the genus Cupressus.
Isolated groves in Arizona & Mexico.
O - R: Old World Cypress (Cupressus).
Including commonly cultivated Italian
Cypress (Cupressus sempervirens).
S: False Cypress (Chamaecyparis)
Including the Port Orford Cedar
Chamaecyparis lawsoniana.
T: Vietnamise Cypress (Xanthocyparis).
Includes Alaska cedar (X. nootkatensis).
Formerly placed in genus Callitropsis.
U: Hybrid Cypress (Xanthocyparis x leylandii).
Alaska Cedar x Monterey cypress. Also
named Cupressocyparis & Cuprocyparis.

A. Tecate cypress (Hesperocyparis forbesii), B. Sargent cypress (H. sargentii), C. Piute cypress (H. nevadensis), D. Cuyamaca cypress (H. stephensonii), E. Santa Cruz cypress (H. abramsiana, F. Monterey cypress (H. macrocarpa), G. Gowen cypress (H. goveniana), H. Mendocino cypress (H. pygmaea), I. Macnab cypress (H. macnabiana), J. Modoc cypress (H. bakeri), K. Smooth-bark Arizona cypress (H. glabra), L. Rough-bark Arizona cypress (H. arizonica), M. San Pedro Martir cypress (H. montana), N. Mexican cypress (H. lusitanica), O. Italian cypress (Cupressus. sempervirens), P. Sahara cypress (C. dupreziana), Q. Kashmir cypress (C. cashmeriana), R. Mourning cypress (C. funebris), S. Port Orford cedar (Chamaecyparis lawsoniana), T. Nootka cypress or Alaska cedar (Xanthocyparis nootkatensis), U. Leyland cypress (Xanthocyparis x leylandii) also listed as Cupressocyparis leylandii and Cuprocyparis leylandii) in nursery trade.

Note: The Port Orford cedar (S) remains in the genus Chamaecyparis, while the and Alaska cedar (T) is now placed in the genus Xanthocyparis, while the Leyland cypress (U) becomes Xanthocyparis x leylandii or Cuprocyparis leylandii in some references. Groupings of species, such as Hesperocyparis, Xanthocyparis, Chamaecyparis, Juniperus and Old World Cupressus represent separate branches (clades) in computer-generated phylogenetic trees.

Yours truly high in the Sierra de San Pedro Mártir, Baja Calif. in search of the rare, endemic San Pedro Martir Cypress, Hesperocyparis (Cupresssus) montana. This isolated species on the Baja California peninsula has also been listed as a subspecies of the Arizona cypress (Cupressus arizonica).

  Cupressus: Remarkable Conifers Native To California
   Selection & Genetic Drift In Cypresses (Cupressus)

This appears to be Hinoki cypress (Chamecyparis obtusa) native to Japan. One specimen is located on the main campus. A larger female (seed) cone is shown. The smaller male (pollen) cones are produced at the branchlet tips (black arrow). Some botanists have merged the genus Chamaecyparis with the genus Cupressus, although it is still commonly listed under Chamaecyparis in the nursery trade. There are several named cultivars of this species.

Oriental arborvitae (Platycladus orientalis), formerly Thuja orientalis.

Two species of Australian cypress pines (Callitris): A. Callitris preissii (C. robusta) and B. Callitris columellaris. Their foliage and seed cones greatly resemble our North American cypress (Cupressus). The large boulders contain colonies of the black crustose lichen Verrucaria nigrescens.

  Black Crustose Lichens In The Palomar College Arboretum  

Left: Tolleson's blue weeping juniper (Juniperus scopulorum 'tolleson's weeping' ). The seed cones of junipers are fleshy, compared with the woody cones of Cupressus. Right: Mexican cypress (Cupressus lusitanica). Note: Based on DNA evidence, the generic name Callitropsis has been proposed for New Word species of Cupressus.

Podocarpus Family (Podocarpaceae)

Podocarpus gracilior, a member of the Podocarpaceae native to eastern Africa. Although it is sometimes called "fern pine" it does not belong to the genus (Pinus); however, like pines and other cone-bearing species, it does belong to the division Coniferophyta. Small female cones are composed of 2-4 reduced scales, but usually only one scale bears an ovule that matures into a seed. There is little resemblance to a cone in the mature seed. The seed has a hard coat surrounded by a fleshy outer layer (aril). The drupelike seed often sits on a fleshy red or purple base or cone axis that is called an aril in some references. The seeds are similar to the California nutmeg (Torreya californica) and Pacific yew (Taxus brevifolia), members of the closely-related yew family (Taxaceae). In the latter species, the naked seed sits partially exposed in a red, cup-shaped aril. Podocarpus seeds are often referred to as fleshy fruits called drupes, but this is incorrect because drupes develop from the ovaries of flowering plants. Another group of conifers with fleshy seed-bearing structures are the junipers (Juniperus) in the cypress family (Cupressaceae). Junipers actually produce small cones with fleshy, fused scales bearing one-several seeds. Podocarpus is a dioecious species, with separate male and female trees in the population. Podocarpus has an ancient lineage dating back to distant relatives that lived during the Jurassic Period 170 million years ago.

  Calif. Nutmeg (Torreya) and Pacific Yew (Taxus) in the Taxaceae  
Calif. Nutmeg (Torreya californica) in Sequoia Nat. Park
See the Pacific Yew (Taxus brevifolia) in Montana   

Cycad Family (Zamiaceae)

Macrozamia johnsonii near the Patron's Pavilion. This beautiful cycad is native to New South Wales.

Male cones of Zamia furfuracea, an interesting cycad native to eastern Mexico. Like some of the other species in this genus, the main trunk is partly or completely subterranean with leaves arising from near the ground level. The cone scales have pollen-bearing sporangia on their underside. After landing on the scales of receptive female (ovulate) cones, the grains develop into pollen tubes that grow toward the egg-bearing ovules. The multiciliate sperm of Zamia species are some of the largest in the world, and in Z. roezlii they are actually visible to the naked eye. Several species of Zamia are native to the southeastern United States (mainly Florida), including Z. integrifolia, Z. floridana and Z. pumila, although some of these may only be variants of Z. integrifolia. The starchy pith of Florida cycads was collected by Seminole Indians and used to make a type of bread. It is known as sago starch or Florida arrowroot. Although once common in their natural habitats, the native populations of these species have been greatly reduced due to poaching and overcollecting. Some of these species are commonly cultivated in southern California, especially in tubs and planter boxes with well-drained soils.

  Cycads That Lived With Dinosaurs  
Cycads: Plants Of Jurassic Park
Cycads & Continental Drift
Plants Of Jurassic Park


  1. Armstrong, W.P. 2010. The Araucaria Family: Past & Present. Pacific Horticulture 71 (1): 4-11. Pacific Horticulture January 2010)

  2. Armstrong, W.P. 1978. "Southern California's Vanishing Cypresses." Fremontia 6 (2): 24-29.

  3. Armstrong, W.P. 1977. "The Close-Cone Pines and Cypresses" (Chapter 9, pp. 295-358). In: Terrestrial Vegetation of California, John Wiley & Sons.

  4. Armstrong, W.P. 1966. Ecological and Taxonomic Relationships of Cupressus in Southern California. MA Thesis, Biological Science Department. California State College at Los Angeles.

  5. Farjon, A. et al. 2002. "A New Genus and Species in the Cupressaceae (Coniferales) from Northern Vietnam, Xanthocyparis vietnamensis." Novon 12: 179-189.

  6. Griffin, J.R. and W.B. Critchfield. 1972. The Distribution of Forest Trees in California. USDA Forest Service Research Paper PSW 82. Berkeley, California.

  7. Hickman, J.C. (Editor). 1993. The Jepson Manual: Higher Plants of California. University of California Press, Berkeley.

  8. Lanner, R.M. 1999. Conifers of California. Cachuma Press, Los Olivos, California.

  9. Little, D.P. et al. 2004. "The Circumscription and Phylogenetic Relationships of Callitropsis and the Newly Described Genus Xanthocyparis (Cupressaceae)." American Journal of Botany 91: 1872-1881.

  10. Little, D.P. 2006. "Evolution and Circumscription of the True Cypresses (Cupressaceae: Cupressus)." Systematic Botany 31: 461-480.

  11. Little, E.L., Jr. 1953. Check List of Native and Naturalized Trees of the United States. USDA Forest Service Agriculture Handbook No. 41, Washington, D.C.

  12. Wolf, C.B. 1948. "Taxonomic and Distributional Studies of the New World Cypresses." El Aliso 1: 1-250.