Cupressus

Common Names

Cypress (Eckenwalder 1993).

Taxonomic Notes

Cupressus has been a hot topic in conifer systematics through most of the 21st Century, with various proposals to subdivide it into multiple genera. I will not belabor the history of this controversy, but will summarize it as follows:

• 2002: Farjon et al. describe a new cypress species from Vietnam, assigning it to a new genus, Xanthocyparis. They also take one of the most unconventional species of Cupressus, C. nootkatensis (assigned by some to Chamaecyparis), and assign it to the new genus.
• 2006: Little, performing detailed molecular analysis of all species in the genus, reveals that Cupressus is paraphyletic (cladogram shown at left). This is further discussed below, but briefly, Little's work shows that the New World cypresses diverged from a clade that later produced Juniperus. He assigns the New World cypresses and X. nootkatensis to the genus Callitropsis (an old name for X. nootkatensis).
• 2009: Debreczy et al. assign X. nootkatensis to the monotypic genus Callitropsis and assign the remaining New World cypresses to a new genus, Hesperocyparis.

The debate principally centers around the cladogram shown at left, which is almost entirely based upon evidence from molecular data, i.e., evidence derived from sequencing portions of the DNA from each species represented. The cladogram shows degrees of similarity between existing taxa, but it can also be interpreted as a representation of the phylogeny of these taxa. Under that interpretation an ancestral cypress gave rise to two lineages, in the Old and the New World. The Old World lineage shortly thereafter gave rise to the junipers, which underwent rapid evolutionary radiation and have since become far more ecologically successful than the cypresses; later, the existing species of Old World cypresses arose. Meanwhile, the New World cypresses soon gave rise to Xanthocyparis (or Callitropsis), and somewhat later the existing species of New World cypresses evolved.

What we do about this depends partly on whether the cladogram does, in fact, represent the phylogeny of sixty-odd modern species. As noted above, the cladogram is based almost exclusively upon evidence derived from sequencing the DNA in the various modern species represented. Those data are then processed in a very rigidly specified, unbiased manner to produce the cladogram. However, past experience with the Cupressaceae has shown that measured DNA data are only partial estimators of actual genetic relationships; consequently, interpretation of relationships between genera within the family, and relationships between species in each genus, has changed continuously over the years as new DNA data became available. Sometimes these interpretations have changed because different types of genetic material have been analyzed (for instance, chloroplast vs. nuclear ribosomal material); sometimes they have changed because different portions of the DNA genome have been studied. The interested reader can see this by reviewing the studies by Gadek and Quinn 1993, Brunsfeld et al. 1994, Gadek et al. 2000, Little et al. (2004), and Little (2006); many other studies show a comparable progression of understanding based on analysis of genetic material in Juniperus.

In view of the existing uncertainty about the accuracy of the cladogram shown here, I have for the time being decided to include Hesperocyparis in synonymy with Cupressus. My reasons for this decision are not entirely scientific. The New World species of Cupressus are of great social and economic importance; they have used horticulturally for almost 400 years (C. lusitanica, brought to Portugal in 1634) and have been described as species of Cupressus for more than 200 years. It will cause considerable upheaval (and annoyance) in the horticultural community if these species are reassigned to Hesperocyparis. Accordingly, it is appropriate to demand a high standard of proof before making such a change, and the limited molecular work performed to date does not in my opinion meet that standard. No harm will be done if a few more years are spent in study and discussion before making such an important nomenclatural change. As a secondary matter, it is not strictly necessary to subdivide Cupressus even if it is shown to be paraphyletic; there is as yet no rule in botanical nomenclature prohibiting paraphyletic genera, and as a practical matter, there is little risk that anyone interested in the evolution of Cupressus will remain ignorant of the fundamental division between Old and New World species.

I now turn to the other debate, regarding the number of species in the genus.

Cupressus as described here contains 28 taxa, all of which have been described as species but many of which have been reduced to subspecies or varieties on debatable grounds. The large range of opinion occurs because cypresses generally occur in small isolated populations distinguished by small differences, interpreted by some as valid at species rank, but by others only at varietal or subspecific rank. Analyses performed in the 1990s using morphological and chemical data (e.g. Frankis 1992, Eckenwalder 1993, Farjon 2005) tended to "lump" taxa into a relatively small number of species (as few as 12). Conversely, the more narrow species concept was early advocated by Wolf (1948) in his monograph on the New World cypresses and was later supported by Rushforth (1987) and, for the California species, by Lanner (1999). A more recent analysis using morphological, chemical and multiple lines of molecular/genetic data (Little 2006) determined that many of the isolated populations are sufficiently distinct to be regarded as discrete species. Those findings are summarized in the cladogram shown here.

I have chosen, on the basis of these findings, to recognize certain taxa as good species, while retaining others as subspecies or varieties. The close relationship between the varieties of C. goveniana appears to be well supported, and is here retained. However, taxa that have been treated as varieties of C. arizonica in recent treatments (Eckenwalder 1993, Farjon 2005) all may warrant species rank, or more particularly, may be more closely related to other species (such as C. lusitanica and C. guadalupensis) but have not yet been so described. A similar problem applies to C. forbesii, formerly treated as a variety of C. guadalupensis but now seeming to be just as closely related to C. stephensonii. Indeed, these taxa represent a significant, persistent taxonomic problem that dogs the taxa here treated as C. arizonica, C. benthamii, C. forbesii, C. guadalupensis, C. lusitanica, C. montana, C. nevadensis and C. stephensonii: namely, that all of these taxa appear to represent a species complex rooted in northwest Mexico, an area which has not been adequately studied. Fully understanding how these taxa are related, and whether any of them can be meaningfully distinguished as separate species, awaits comprehensive study of the many geographically distinct Cupressus populations in this vast area.

Description

Trees or large shrubs, evergreen. Branchlets terete or quadrangular, in decussate arrays in most species; flattened (comblike), superficially resembling Chamaecyparis or Thuja in others. Leaves opposite decussate in 4 ranks, rarely in alternating whorls of 3 in 6 ranks. Adult leaves appressed to divergent, scalelike, rhomboid, free portion of long-shoot leaves to 4 mm; abaxial gland present or absent. Pollen cones with 4-10 pairs of sporophylls, each sporophyll with 3-10 pollen sacs. Seed cones maturing in (?1-)2 years, exact maturation period poorly researched, mostly varying from about 16-25 months after pollination; generally persisting closed many years or until opened by fire, but opening on maturity, and falling soon after seed release, in a few species; globose or oblong, 8-43 mm; scales persistent, (2)3-6(7) opposite decussate pairs, valvate, peltate, thick and woody, the terminal pair either fused or open with a small central columella (varying from cone to cone on a single tree). Seeds (3)5-20 per scale, lenticular or faceted, narrowly 2-winged; cotyledons 2-5. x= 11 (Eckenwalder 1993, Frankis 1999).

Range

Warm north temperate regions (Eckenwalder 1993): W USA, Mexico and adjoining Central America, NW Africa, Middle East and eastward along the Himalaya to SW & Central China and N Vietnam.

Big Tree

There are no good data for a variety of species, but of the documented ones, Cupressus gigantea seems the clear winner, followed by Cupressus macrocarpa.

Oldest

There are few age data on Cupressus in general. Based on habitat (trees native to desert mountains tend to live a very long time), I suspect C. dupreziana (Frankis 1999) may attain great ages.

Dendrochronology

Several species have proven useful in climate reconstruction, archeological dating, and ecological studies. The genus appears to be less intractable than most of the Cupressaceae with regard to such problems as poor ring boundaries, false rings, and poor circuit uniformity. See the individual species for details.

Ethnobotany

Several species are of horticultural importance; fastigiate forms of C. sempervirens, C. duclouxiana and C. funebris have been cultivated for ornament for several thousand years in the Mediterranean region and S China respectively, and the highly decorative weeping C. cashmeriana similarly long around Buddhist temples in Sikkim, Bhutan, Assam and nearby areas of Tibet and India.

The wood is valued for its sweet scent and resistance to decay. Famous uses of the wood (of C. sempervirens) include Noah's Ark (The Bible, Genesis 6:14), and the doors to St. Peter's, Vatican City, Rome, which were still sound after 1,100 years' use (Loudon, 1838; reference misplaced).

Observations

Remarks

The genus name is from the Roman name for C. sempervirens, itself a loan word via Greek Kuparissos from Hebrew Gopher (Frankis 1992).

Citations

Debreczy, Z., K. Musial, R.A. Price, and I. Racz. 2009. Relationships and nomenclatural status of the Nootka cypress (Callitropsis nootkatensis, Cupressaceae).

Frankis, M.P. 1992. Cupressus. In: Griffiths et al. (eds) The New RHS Dictionary of Gardening 1: 781-783.

Frankis, M.P. 1999. Contributions based on personal experience, via e-mail, 1999.02.03.

See Also

The Cupressus Conservation Project provides a wealth of information on old and new world Cupressus, including a taxonomic review, historical accounts, cone photographs, and various other pertinent information.

Farjon (2005) provides a detailed account.

Farjon, A. 2009. Do we have to chop up the cypresses? Conifer Quarterly 26(4):12-17.

Goggans, J.F. and C.E. Posey. 1968. Variation in seeds and ovulate cones of some species and varieties of Cupressus. Circ. Agric. Exp. Sta., Alabama 160:1-23.

Little (1966).

Little (1970).

Little et al. (2004).

Masters, M.T. 1896. A general view of the genus Cupressus. Journal of the Linnaean Society, Botany 31: 312-363. http://www.cupressus.net/Masters.html, courtesy of the Cupressus Conservation Project website.

Silba 1981.

Silba, J. 1998. A monograph of the genus Cupressus L. Journal of the International Conifer Preservation Society 5(2):1-98.

Wolf (1948).

This page co-edited with M.P. Frankis, 1999.02.