Päiväkirja-arkisto kohteelle kesäkuu 2018

26. kesäkuuta 2018

Two Erigeron in PA

Erigeron annuus and Erigeron strigosus are the two Erigeron species in PA with tapering leaf bases (rather than clasping leaves).

Flora of PA treatment uses vague descriptors to distinguish them (what constitutes "numerous leaves"?) that might be useful once the user is already familiar with the two.

Flora of North America entry (Guy Nesom, 2004) quickly distinguishes them from other Erigeron based on lack of pappus on ray florets, but not disc florets . This is pictured in my observation.
It then emphasizes stem vestiture, which might not be visible in many observations on iNaturalist. Even this emphasis includes quite a bit of overlap, apparently to accommodate some varieties of E. strigosus and to accommodate the fact that E. annuus sometimes has strigose hairs too.

Michigan Flora gets around this problem by ignoring the problematic E. strigosus var. septentrionalis (associating it with some forms of E. annuus), which makes for a cleaner couplet, but who knows? it might be an oversimplification:

"E. annuus: Middle region of stem glabrate to pubescent with all or many of the hairs long (0.5–1.2 mm) and spreading; principal cauline leaves usually elliptic to ovate, ca. 10–35 (–40) mm wide, with a few large teeth.

E. strigosus: Middle region of stem moderately to densely pubescent with only short (0.5 mm or less) mostly appressed-antrorse hairs; principal cauline leaves linear to oblanceolate, ca. 2.5–10 (–15) mm wide, entire."


Lähetetty 26. kesäkuuta 2018 00:34 käyttäjältä ddennism ddennism | 2 havaintoa | 0 kommenttia | Jätä kommentti