July 26, 2019

Case study: Erigeron

I have two specimens and two species. E. arizonicus from Oracle ridge and what I think is E. oreophilus from radio ridge. Maybe I will be able to definitely confirm E. oreophilus before all this is done.

Note - it turns out that this is E. superbus rather than E. arizonicus.

Key out E. arizonicus using Arizona Flora

Start on page 830 
Corollas bilabiate? No.
All ray flowers? No.
Rays present? Yes.
Pappus of capillary bristles? Yes. -- group F
Now the key for group F on page 836. I see Erigeron in the list, so I haven't screwed up yet. 
Rays white or violet? Yes.
Leaves and ivolucre marked with translucent oil glands? No.
Pappus with 1 or 2 bristles? No, there are lots.
Ray achenes enveloped by the phyllaries? No.
Ray flowers have pappus? Yes.
Plants dwarf? No.
Style tips -- lanceolate or deltoid?
The final question is tricky. My head is young and most flowers have not opened yet. I manage to take apart a flower and the style tips look blunt, deltoid, or rounded. There are other criteria at this point in the key. Are the phyllaries strongly graduated or fairly equal (mine are equal). Are the ray flowers numerous and narrow? Mine are. This makes it Erigeron rather than Aster.

Arizona has 32 species of Erigeron, the key is on page 874. 

Rays present and conspicuous? Yes.
Stem leaves pinnatifid or entire? Entire.
Plant large and coarse, disk 1 cm or bigger?  Yes, my disk is 1 cm.
Stem leafy to the inflorescence or bare? Leafy.
Stem glabrous or glandular-puberulent? Glandular-puberulent.
Stem hirsute as well as gladular-puberulent.  No.
This makes it E. superbus! If it did not have leaves up to the inflorescence we could get to E. arizonicus -- but that is described as cinereous-pilose. My plant is clearly covered with glandular hairs. What a surprise!

Now what about my E. oreophilus?

The keys take us to the Erigeron genus the same way, then: 
Rays present and conspicuous? Yes.
Stem leaves pinnatifid or entire? Pinnatifid.
Stem hispid or glandular-puberulous.  Glandular-puberulous.
The stem on my specimen is covered with glandular hairs and has some hirsute bristles lower on the branch, so it is E. oreophilus. The other choice at the last question would make it E. neomexicanus if it was not glandular (so there is the way to tell, use a hand lens and look for glandular hairs).

More about Erigeron is southern Arizona

E. superbus is reported from the Huachucas and Pinalenos as is E. rusbyi. Also worth keeping an eye out for are E. concinnus, E. pringlei, E. lemmoni, and more! Who would have thought there are so many Erigeron to worry about. It makes me want to visit the Huachucas and Santa Ritas to inspect their Erigerons.
Have any comments? Questions? Drop me a line!

Tom's Plant pages / tom@mmto.org