California Cypresses

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The True Cypresses (Genus Cupressus = Hesperocyparis)
Isolated Groves In Western North America

© W.P. Armstrong 30 May 2008

Millions of years ago, cypress woodlands containing one or more ancestral species of the cone-bearing genus Cupressus once dominated vast areas of California. During the past 20 million years, as mountains were uplifted and the climate became increasingly more arid, most of these extensive cypress woodlands vanished from the landscape. In some areas, the cypress were probably unable to compete with more drought resistant, aggressive species, such as impenetrable chaparral shrubs and desert scrub. Although cypress are fire-adapted with serotinous seed cones that open after a fire, they are vulnerable if the fire interval occurs too frequently, before the trees are old enough to produce a sufficient cone crop. Chaparral shrubs quickly resprout after a fast-moving brush fire from well-established subterranean lignotubers. This may explain why some cypress groves occur in very rocky, sterile sites with poor soils where the chaparral shrubs can't compete as well.

Shrubby macnab cypress (Cupressus macnabiana) growing on a barren serpentine outcrop near Magalia (Butte County, California). The tall pine with sparse foliage is Pinus sabiniana.

See Article About Brush Fires In California

The present-day world distribution of cypress (Cupressus) includes North and Central America, Africa, Middle East and eastward along the Himalayas to China and North Vietnam. For thousands of years, Italian cypress (C. sempervirens) and mourning cypress (C. funebris) have been grown as ornamentals in the Mediterranean region and southern China. The beautiful, weeping Kashmir cypress (C. cashmeriana) has been cultivated around Buddhist Temples in Sikkim, Bhutan, Assam and nearby areas of Tibet and India. In Rome, the Church of Santa Sabina was built in the 5th century AD. The original door was made of Italian cypress with intricate carvings illustrating scenes from the Old and New Testaments. Whether or not cypress wood was used in the construction of Noah's Arc (Genesis 6:14) has been debated by biblical scholars for centuries. Italian cypress grew abundantly in the Middle East, and the seasoned timbers were very durable.

A block of seasoned wood from the Italian cypress (Cupressus sempervirens). The attractive knots in this durable wood are the remnants of numerous small branches that arise from the main trunk.

In California, cypress trees often grow on sterile, rocky outcrops. One of these rock types is serpentine (also called serpentinite) a greenish, shiny rock that is exposed throughout the Coast Ranges of central and northern California, and the Sierra Nevada foothills. According to the California Geological Survey, serpentine has been designated California's official state rock. Serpentine is a magnesium silicate rock with a waxy luster and a shiny, marblelike appearance. It varies from cream white through all shades of green to black. Higher grade, deeply-colored serpentines are used for animal carvings, particularly in Africa. Some polished serpentines resemble jade in color and are used in pendants and rings.

Serpentine from the Coast Ranges of central and northern California. Serpentine is a shiny rock with a waxy luster and feel. It varies in color from creamy white and shades of green to black. In California, many species of rare and endangered plants are endemic to serpentine outcrops, including the California cypress.

A 30 pound hippo carved from a chunk of African serpentine.

The distribution of some California cypress species, such as the Sargent cypress (Cupressus sargentii) and Macnab cypress (C. macnabiana) coincide nicely with serpentine outcrops. Other impoverished soil types include barren sandstone and metavolcanic rock. Cypress trees growing on rugged, rocky soils in the wild appear to be better anchored and able to withstand strong winds and rain, compared with top-heavy cultivated cypress in rain-soaked, loam soils.

A grove of Sargent cypress (Cupressus sargentii) in the San Rafael Mountains of Santa Barbara County, California. This species typically grows on outcrops of serpentine in the Coast Ranges of central and northern California. Genetic drift has undoubtedly occured in isolated cypress groves such as this one, which are often referred to as "arboreal islands."


Selection & Genetic Drift In California Cypress

Today this fascinating genus is represented by 10 species (or 8 species and 2 subspecies), confined to isolated groves scattered throughout the coastal and inland mountains, from the Mexican border to Oregon. Because some of these populations became isolated into "arboreal islands," gradual genetic changes over millions of years resulted in the present-day species and subspecies. It is quite likely that natural selection played a role in cypress speciation. Cypress of arid inland mountains and valleys (such as Piute cypress, Macnab cypress, Cuyamaca cypress, and Arizona cypress) have glandular (resinous) foliage and are more drought resistant. Coastal species (such as Monterey cypress, Gowen cypress, Santa Cruz cypress and Mendocino cypress) are generally nonglandular without resin glands on the leaf surfaces. Some phenotypic variability, particularly between different isolated groves of the same species may be due (in part) to genetic drift. These differences include slight variations in foliage, bark characteristics (exfoliating vs. persistent), and the general shape of seed cones. Differences attributed to genetic drift are analogous to racial differences in people, such as different blood type percentages and facial characteristics.

A. Foliage and pollen cones of the Smooth-bark Arizona cypress (Cupressus glabra) [Syn. C. arizonica ssp. glabra]. B. Foliage of the Tecate cypress (C. forbesii). The scalelike leaves of Arizona cypress are glaucous and very glandular (sticky). The scalelike leaves of Tecate cypress are green and without dorsal resin glands.

Bark variation in California cypresses. A. Persistent, shreddy bark of Piute cypress (C. nevadensis). B. Exfoliating bark of Cuyamaca cypress (C. stephensonii).

The relatively short period of isolation for Cupressus (cypress) species may be one of the reasons taxonomists disagree on the total number of species native to North America. In 1948, Carl B. Wolf published his "Taxonomic and Distributional Studies of the New World Cypresses" (El Aliso 1: 1-250). Dr. Wolf listed a total of 15 species, one in Baja California, one on Guadalupe Island off the coast of Baja California, one in Mexico and Central America, two in Arizona, and 10 in California. In 1953, the number of U.S. species was reduced to six by Dr. Elbert Little, Jr. in his Check List of Native and Naturalized Trees of the United States (USDA Agriculture Handbook No. 41). These numbers have fluctuated greatly in subsequent publications. In addition, the nursery trade has added several cultivated varieties, including at least four different cultivars for the Arizona cypress.

Left: Monterey cypress (Cupressus macrocarpa) in Point Lobos State Park on the coast of central California. Right: Grove of Piute cypress (C. nevadensis) in the Piute Mountains, with Lake Isabella and the snow-covered Sierra Nevada in the distance. The Piute cypress are more drought resistant, with gray (glaucous), glandular (resinous) foliage similar to the Arizona cypress. In fact, some botanists now consider the Piute cypress to be a subspecies of the Arizona cypress and have named it C. arizonica ssp. nevadensis.

Smooth-bark Arizona cypress (Cupressus glabra) along scenic Oak Creek Canyon, Arizona. The cypress have glaucous, glandular foliage and exfoliating bark.
Evidence from DNA sequencing has further complicated the number of cypress species, including the transfer of other conifer genera into the genus Cupressus. For example, the Jepson Manual of California Plants lists ten species; however, two of these C. nootkatensis (Alaska cedar) and C. lawsoniana (Port Orford cedar) were formerly placed in the genus Chamaecyparis. These two genera are obviously closely related to Cupressus. In addition to their similar seed cones, they are also genetically compatible. The popular Leyland cypress (Cupressocyparis leylandii) used in landscaping is a bigeneric hybrid between the Monterey cypress (Cupressus macrocarpa) and the Alaska cedar (Chamecyparis nootkatensis).

Update On The Taxonomy Of Cypresses (Cupressaceae)

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. Early in this century, a new cypress species was discovered in 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.

Based on their general morphological appearance, the New World Cupressus 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 Callitropsis, Chamaecyparis, Juniperus and Old World Cupressus represent separate branches (clades) in computer-generated phylogenetic trees.

Sweeping changes in conifer taxonomy are also being proposed at the family level. The results of these studies indicate that a number of genera formerly assigned to the Taxodiaceae now belong in the Cupressaceae. The principle exception is the genus Sciadopitys (Japanase umbella pine), which was found to be completely unlike the Cupressaceae, and is now placed in the monotypic family Sciadopityaceae.

Using DNA to Compare Genera & Species
Homoplasy: Parallel and Convergent Evolution
Australian Callitris in Palomar College Arboretum
  Representatives of the Taxodium Family (Taxodiaceae)  

Alaska cedar (Chamaecyparis nootkatensis) near Government Camp, Oregon.

Although coastal populations of Monterey cypress are resistant to corneum canker, trees planted in the interior valleys are very susceptible to this fungal disease. It is interesting to note that the Leyland cypress has also acquired this fungal susceptibility from its cypress parent. The cypress are a complex genus that still challenge taxonomists. It is possible that some of the disjunct species of Cupressus in California and Arizona have not been isolated long enough to warrant the status of a species. In fact, this is why most modern floras have consolidated four species of the southwestern United States and Baja California into subspecies of the Arizona cypress (C. arizonica). These species have been isolated long enough for genetic drift to occur, but perhaps not long enough for the development of distinct species populations.


Genetic Drift In The Seed Cones Of Cypresses

Seed cones from cypress groves in California & Arizona.

Left: Seed cones from groves in southern California. A. Tecate cypress (C. forbesii) [Syn. C. guadalupensis ssp. forbesii], B. Sargent cypress (C. sargentii), C. Piute cypress (C. nevadensis) [Syn. C. arizonica ssp. nevadensis], D. Cuyamaca cypress (C. stephensonii) [Syn. C. arizonica spp. stephensonii], E. Smooth-bark Arizona cypress (C. glabra) [Syn. C. arizonica ssp. glabra], F. Rough-bark Arizona cypress (C. arizonica) [Syn. C. arizonica ssp. arizonica]. Right: Seed cones from groves in central and northern California. G. Monterey cypress (C. macrocarpa), H. Gowen cypress (C. goveniana) [Syn. C. goveniana ssp. goveniana], I. Santa Cruz cypress (C. abramsiana), J. Sargent cypress (C. sargentii), K. Mendocino cypress (C. pygmaea) [Syn. C. goveniana ssp. pigmaea], L. Macnab cypress (C. macnabiana), M. Modoc cypress (C. bakeri).

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

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

Note: The Port Orford cedar (S) and Alaska cedar (T) are often placed in the genus Chamaecyparis, while the Leyland cypress (U) is placed in the genus Cupressocyparis.


Male (pollen) cones of the Piute cypress (Cupressus nevadensis) [syn. C. arizonica ssp. nevadensis). Each scalelike leaf bears a dorsal gland that exudes a resin droplet (red arrow). Interior cypress species such as this one typically have glaucous, resinous foliage, presumably an adaptation to dry, arid habitats.


References

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

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

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

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

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

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

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

  8. 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.

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

  10. 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.

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

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