Plant Species of San Jacinto Mountain: Erigeron breweri var. covillei, Coville's fleabane

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Botanists have had a hard time deciding where to place the plants corresponding to what is now called Erigeron breweri var. covillei within the E. foliosus - E. breweri complex. This is perhaps not surprising, since Cronquist, who monographed the North American species of Erigeron, north of Mexico, in 1947, wrote

The E. foliosus - E. breweri complex presents some of the most difficult problems in the genus Erigeron. There are a multitude of recognizable forms, often with relatively strong morphological characters, but these interlock and intergrade in such a way that taxonomic segregation becomes difficult, and a completely satisfactory treatment seems impossible.

The plants at San Jacinto Mountain, at least in the variation in their stem hairs, perhaps support the contention by Greene that it should be its own species, E. covillei. Greene defined this taxon in 1895, and wrote

Species in some sort intermediate between E. breweri and E. foliosus, but specifically different from both.

The stem hairs on the plants at San Jacinto Mountain vary between the dense spreading / somewhat deflexed hairs of E. breweri, and the sparse appressed hairs of E. foliosus; see below.

Interesting, Compton, in 1934, moved it to a variety of E. foliosus, as E. foliosus var. covillei, stating

Similar to var. typicus (=E. foliosus var. foliosus) but more gray with a very dense pubescence of coarse, hispid, almost lanceolate hairs.

Neson, in 1992, moved it to a variety of E. breweri, stating

the dense, spreading-deflexed stem pubescence of these plants places them with E. breweri rather than E. foliosus. Further, they are broadly sympatric with E. foliosus var. foliosus and few if any unequivocal intermediates have been seen.

Our plants at San Jacinto Mountain are either the southernmost examples of this taxon, as stated in Nesom, or the next to southernmost examples if the plants from the San Felipe Valley / Volcan Mountain in San Diego County are also this taxon. As such, it is possible that our plants are somewhat different from the bulk of the covillei population to the north, and their stem hair variation has been caused by interbreeding with E. foliosus. The San Jacinto Mountain population of covillei is small in geographic extent, and surrounded by E. foliosus. However, see below for an argument that this variation in its stem hairs is normal within E. breweri var. covillei, since it is seen in other areas as well.

Fig. 1 shows the variation in the stem hairs of Erigeron breweri var. covillei from the PCT north of SR74, in the seven plants photographed on 31 May 2018.

Fig. 1. The variation in the stem hairs for plants on the PCT north of SR74, from typical E. breweri spreading, somewhat deflexed hairs; to ascending hairs; to appressed hairs; and then to sparse hairs. Click on the pictures for larger versions.

The plants near the trailhead, and near mile 1.1, appeared to consist of a single species, all similar in their gestalt and growing in the same habitat in the shade of larger plants. The plants all looked quite different from typical E. foliosus. E. foliosus usually has tall erect stems and linear leaves, with glabrous to sparsely strigose stems. All of the plants here, at both locations, were short, grayish, looking in color and habit like E. breweri.

However, only about half of the plants had the typical dense spreading / somewhat reflexed hairs of E. breweri. The others had hairs of nearly all sorts. Some had sparse / somewhat reflexed hairs; some had dense spreading / somewhat ascending hairs; and some had moderate to dense appressed hairs.

It appears these can all fit E. breweri.

The key to separate these species is:

49. Stem hairs dense, stiffly spreading, generally slightly reflexed ==> E. breweri
49' Stem hairs ± 0 or sparse, appressed ==> E. foliosus

The plants as a whole have mostly dense stem hairs that are mostly spreading. Only one plant out of seven has sparse, appressed hairs, and it still doesn't look like E. foliosus seen elsewhere. It appears that, at least here, the variation in the hairs for E. breweri simply encompasses a few plants having sparse, appressed hairs.

I.e., even though two of the seven plants don't fit the "stiffly spreading" part of the key for E. breweri, they certainly don't fit the "± 0 or sparse, appressed" part of the key for E. foliosus, either.

Interestingly, Nesom found a similar variation in the hairs of E. breweri var. covillei in plants from the area of Independence in Inyo County near the northern part of the range for var. covillei, and Cronquist found similar "intergrades". It may well be that these are part of the normal variation in the hairs for var. covillei.

On 5 June 2018, I studied undisputed plants of E. foliosus along the Ernie Maxwell Trail at San Jacinto Mountain to examine the variation in their stem hairs, and found that some plants had typical E. breweri hairs on their lowermost stems. See example of a plant with spreading hairs on a lower stem and sparse appressed hairs on its upper stem.

Most of the E. breweri plants on the PCT north of SR74 were not yet producing flowers on 31 May 2018. Two of the heads that were about to bloom are shown in Fig. 2.

Fig. 2. Flower heads in bud for two separate plants from the PCT north of SR74. Left: the head corresponding to the plant whose stem hairs are shown at lower right in Fig. 1. Right: the head from a plant at the location of the two plants shown in the right two pictures in the first row in Fig. 1. Click on the pictures for larger versions.

I thank Jordan Zylstra for pointing out a young plant of E. breweri var. covillei at Kenworthy on 4 May 2013, which helped get the ball rolling for me to see and recognize this species. It only took me five years to follow up on it.

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Copyright © 2018 by Tom Chester.
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Updated 6 June 2018.