Plants of Southern California: Achnatherum coronatum / A. parishii
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My experience is that something doesn't seem right in Achnatherum coronatum / A. parishii land. The delineation in the species does not seem correct in many respects. The problem may simply be incorrect descriptions of both taxa, or they may in fact not be separate species.
This page simply gives an alert that there seems to be a problem. However, I have yet to reach any firm conclusions here, and am still collecting more data in order to shed some light on these taxa.
Perhaps the most well-known native grass in Southern California is Achnatherum coronatum, formerly Stipa coronata, giant stipa or giant needlegrass. This grass is often found growing on cliffs along highways, and can usually be easily recognized even while driving in a car at 70 mph from its graceful extremely long flowering stems.
At higher elevations, very similar plants are found that are shorter, and the number of bends in the awn changes from the two bends at lower elevations to a single bend at higher elevations.
If only the stature of the plants changed, this would clearly be considered a single species. However, the qualitative change in the number of bends in the awn has led to the higher elevation plants being described as a separate taxon.
Stipa coronata was first described in 1880 by Thurber, and S. parishii in 1882 by Vasey. S. parishii var. depauperata was described in 1912 by M.E. Jones. I do not know what distinguished var. depauperata from S. parishii, as every flora I've consulted has discarded var. depauperata as being separate from S. parishii.
Davidson (1923) in his Flora of Southern California distinguished S. coronata and S. parishii as follows:plant stout, over 9 dm high .... S. coronata
plant slender, less than 6 dm high.... S. parishii
Davidson placed S. coronata in dry flats in the foothills and S. parishii in the Upper Transition Zone in the mountains.
Hitchcock placed both S. parishii and S. parishii var. depauperata as varieties or subspecies under S. coronata in 1925 and 1934, respectively.
Abrams (1955) distinguished S. coronata and S. parishii as follows:Awn with 2 bends; plants 1 m or more tall .... S. coronata
Awn with usually 1 bend; plant 30-50 cm tall.... S. parishii
Abrams gives a leaf width for S. parishii as about 4 mm, but doesn't give a leaf width for S. coronata. He mentions that the type locality for S. parishii is the San Bernardino Mountains.
Munz (1974) combined S. parishii and S. parishii var. depauperata as S. coronata var. depauperata. The var. depauperata was distinguished by shorter stems, shorter inflorescence, and awns bent once.
The genus was changed to Achnatherum in 1993 by M.E. Barkworth, restoring parishii as a separate species with depauperata as a subspecies. However, in her treatment given in the JM, she discarded var. depauperata as being separate. Her JM key to separate them is:Awn bent twice; basal leaf blade (width) 2.5- 7 mm .... S. coronata
Awn bent once; basal leaf blade (width) 2-3 mm.... S. parishii
I added the key word width which was omitted in the published key. The published description makes it clear that she was talking about the width, although she gives 1.5-3 mm as the leaf width for S. parishii in the description.
It is interesting that Abrams describes the leaf width of S. parishii as about 4 mm, whereas the JM describes its leaf width as 1.5-3 mm.
The basic discriminants between the two species are clearly the number of bends in the awn; the stem height, and possibly the infl height and leaf width. All other characteristics of the species are very similar.
My first inkling that something was amiss was a specimen on the Manzanita Trail in the San Gabriel Mountains. I sampled plants from the same location, and probably even the identical plant, on 7/19/02 and 10/07/03. On 7/19/02, only a single seed was available, which had an awn with two bends, and the measured basal leaf width was 6 mm, both of which clearly keyed to Achnatherum coronatum, using the JM key. However, on 10/7/03, I collected five seeds each with a single bend in their awn, which would then key to Achnatherum parishii, albeit with a problem with the leaf width!
On 8/5/04, I found plants on the Aspen Grove / Fish Creek Trail in the San Bernardino Mountains that had awns with a single bend, but also had a leaf width of 6 mm. That immediately reminded me of the plants on the Manzanita Trail, and I began a program to measure specimens of these two taxa in the future.
On 8/10/04 I collected data from a number of specimens at two locations on the Fish Creek Trail, mile 0.16 and mile ~1.50. These plants, all with awns with a single bend with short inflorescence lengths, are all presumably A. parishii, whose type specimen was from these same mountains.
On 8/14/04, I measured a number of inflorescences from very clear A. coronatum plants found along Mt. Baldy Road in the San Gabriel Mountains. I measured a couple of random inflorescences, then intentionally measured the longest and shortest stems I could find.
On 8/17/04, I measured inflorescences from clear A. coronatum at Temecula Gorge at the Santa Margarita Ecological Reserve. Again, I measured a couple of random inflorescences, then intentionally measured the longest and shortest stems I could find.
The leaf widths of each plant are plotted versus the number of bends in the awn in the following figure, along with the parameters given in the floras for the two taxa:
The plant that changed its number of bends in its awn from 2002 to 2003 is plotted twice in the above figure, with its leaf width varying from 6.0 to 7.0 mm.
The leaf width range given in the JM for A. coronatum is not too far off, but clearly does not encompass the maximum leaf widths. However, the leaf width range for A. parishii bears very little resemblance to that given in the JM. In fact, a much better description of my data for A. parishii would be to use the range given in the JM for A. coronatum!
Data from the inflorescences from both sets of plants are plotted in the following figure, along with the parameters given in the floras:
Data points for the plant that changed its number of bends in its awn from 2002 to 2003 are surrounded by a black square and connected by a hard-to-see black line.
This plot shows that the stem lengths for the two taxa are consistent with the ranges given in the JM. However, the inflorescence lengths for A. parishii specimens extends well outside the range given in the JM, showing significant intrusion into the A. coronatum range.
Clearly, all is not well in Achnatherum coronatum / A. parishii land.
Another way to look at this problem is to consider the identification of the A. parishii specimens from Fish Creek.
In Munz, from the stem lengths and number of bends in the awn, these plants would be pretty good examples of Achnatherum coronatum var. depauperata, which is a synonym of A. parishii. However, the inflorescence length is in-between the two taxa.
In the JM, the id is unclear. The leaf width, stem length and inflorescence length clearly go to A. coronatum, but the number of bends in the awns just as clearly goes to A. parishii.
Such troubles are usually an indication that the floras have the species wrong, and there is only a single species. The simplest interpretation of my (insufficient) data is that there is only a single species here, and the awn tends to have only a single bend for the plants found in the higher altitudes of the mountains that have shorter stems and inflorescences.
However, it is far too early for me to reach any conclusions here, and I will continue to collect data to see what the true story is here. Since these are widespread species, it shouldn't take too long to get the answer. Stay tuned!
Copyright © 2004 by Tom Chester
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Comments and feedback: Tom Chester
Last update: 11 October 2004