Friday, November 11, 2011

How many species of Santa Cruz Cypress are there?

Botanists have not agreed upon use of categories to classify hierarchical variation pattern.  As I see it, trinomials are a type of botanical hedge-fund.  We name a taxon (‘we buy it’), then we purchase a derivative against its being ‘lumped’ as a hedge by treating it as an infrataxon.  Moreover, there are no regulatory mechanisms governing the choice of category in the hierarchy.  Sound familiarly like a financial meltdown?  Some authors publish boatloads of new combinations because it is their habit to use solely a single category of infrataxon.  Literature pollution?

The utility of recognizing infrataxa is not well codified in modern usage.  Hamilton & Reichard (1) document the fact that most taxonomists employ only a single hierarchical category below the rank of species, and that two schools of thought are evident: those whom use the category “subspecies” or those that use “variety”. but few botanists use both.  As Fosberg (2) notes there is no specific prohibition against the practice, perhaps due to an instinctive aversion to quadranomials.  The vast majority of authors fail to provide a rationale for their choice of infraspecific category, or for their viewpoint upon the question of parsing variation into a hierarchical topology. 

Recently, the question arises in the case of the Santa Cruz Cypress. and endangered tree: Silba (3) named 5 subspecies.  Adams & Bartel (4), eventually after some hemming, treat 2.  One might choose to treat the Silba infrataxa as varieties within subspecies; others would want to make them formae (although the nature of forma seem to lack consensus in the literature: mostly forma are taken to be sporadic, rare phenotypes that may not have a genetic basis, that is, the condition may be developmental; or, their genetic basis is viewed as a mutation, albinism in flower color is an example.    There is arboricultural utility in considering the Silba infrataxa as cultivars would be o.k. as “C.V.” would eliminate confusion, but unfortunately horticultural nomenclature in practice is in my experience inaccurate.

Fernald (5) would probably have treated H. abramsiana ssp. abramsiana and within it H. abramsiana var. locatellii, H. abramsiana var. neolomondensis and H. abramsiana var. opleri, and H. abramsiana ssp. butanoensis. 

I could question the decision as to how to parse variation within H. abramsiana by noting that for some individuals of ‘neolomondensis’ their chemical profile was as distinct as is ssp. butanoensis, and ‘opleri’ was about as removed in the ISSR ordination but it also differed in mean cone width, length and number of scales.  Faced with practical necessity, the Adams and Bartel treatment is useful, but one could also craft an alternative classification just as readily. 

The pattern of relationships Adams & Bartel find are suggestive of genetic drift following upon segmentation of a variable, ancestral panmictic population: in some respects, one answer is there are either no subspecies of Santa Cruz cypress, but there are five groves.

I will also make reference to the choice between treating these plants in Cupressus as has been traditionally done: Little (6) made out our cypresses to be polyphylletic  within Cupressus.  By aversion to lumping them into Juniperus (6) out Hesperocyparis was cleaved.  There is also evidence that all cupressus are a single clade (7)  I like the latter approach because by their very nature genera are small (8) and in this instance the Hesperocyparis-Cupressus division is a deep one. 

1. Hamilton, C. and S. Reichard.  1992.  Taxon 41:485-498
2. Fosberg, F. 1942.  Rhodora 44:153-157
3.  Silba, J.  2003 Intern. Conifer Pres. Society 10:1-49
4.  Adams, R and J Bartel. 2009 Phytologia 91(2):287-299
5.  Fernald. M. 1941.  Rhodora 43:156-167.
6. Little, D. 2006 Syst. Bot. 31:461-480.
7. Mao, K. et al. 2010.  New Phytologist 188: 254–272
8.  Cronk, Q.C.B. 1989.  Taxon 38(3):357-370.

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