Tuesday, October 27, 2009

Tall Alpine Aster (Oreostemma elatum) does not occur at Yuba Pass?

Oreostemma is a distinctive genus of aster: rosettes, taprooted, mesophytic. The center of origin [sensu Fernald] is doubtless in the "Nevadaplano" – the himalaya-like mountains of California and Nevada that are now thought to be presently lower in elevation by perhaps 2000 meters than they were in the past

Orestemma elatum is reported from Yuba Pass, Sierra County, based on a specimen collected by J.T. Howell on August 21, 1951 (RSA88401, there would doubtless be a CAS duplicate, but that important collection is not databased).

Orestemma elatum is distinguished from O. alpigenum on the basis it its lack of pubescence, three-veined outer phyllaries, which are often indurate-stramineous at the base.

On August 4, 2009 I visited Yuba Pass summit to recollect (#20731) material of the reported occurrence: I found that the plants at this station do not exhibit features of Orestemma elatum, but rather are the low-elevation tall race of O. alpigenum [which may, or may not, deserve a name] – they are pubescent, their phyllaries are one-nerved [see the photo] and not markedly stramenous proximally.

At elevation in the High Sierra, O. alpigenum has a distinctive and relatively constant growth habit: relatively narrow leaves (2-4 mm) and short scapes (<2dm) that are usually partially decumbent. By contrast, the growth habit of plants in montane fen habitats are markedly different: wider leaves (10 mm), tall scapes (to 3 dm) that are generally erect. The aggregate differences make suggest two natural taxa are masquerading under the name O. alpigenum, but it remains to be demonstrated if the differences in habit are not clinal.

Long ago, once upon a time, I learned from John Thomas Howell that it was often most effective [provocative even] to apply a not-exactly-correct name to a specimen in the vain hope (not in all instances is such hope vain) that an outlier would attract the attention of a monographer. I can see how JTH would have used the name O. elatum for his collection: after all, he had the most experience with O. alpigenum throughout the High Sierra, and would have recognized the gross differences in habit between the low, narrow leaved alpine meadow plants and these mid-elevation, tall herbs.

No comments: