14 May, 2019

Distinguishing Equisetum pratense from Equisetum arvense

These two species can be tricky to separate in the field, and certainly from photos. In Northeastern North America, E. pratense is generally uncommon or rare, while E. arvense is abundant most everywhere. It stands to reason that E. arvense will appear much more frequently in observations on INat. There is, however, a bit of confusion on INat ID's.

The best guide I have found to distinguish these species is Peterson "Ferns" of Northeastern and Central NA (second edition). This book includes information published in the Flora of North America account, and is less technical than Flora Novae Angliae. The latter, however, includes useful field characters not found elsewhere, so is definitely worth consulting as well.

Most accounts generally describe E. pratense as more 'delicate' with horizontal or drooping branches, while E. arvense tends to be coarser with ascending (or horizontal) branches. This is a subtle feature, and takes field experience, though it can be a first clue to look closer at the stem, teeth, and branches.

I have posted a closeup of E. pratense and discussion here https://www.inaturalist.org/observations/25076243 that includes some of the following characters to distinguish it from E. arvense.

E. pratense in contrast to E. arvense should show:
1) white-margined (vs. essentially black) sheath teeth
2) distinctly scabrous stem (vs smooth or slightly scabrous)
3) more sheath teeth (than E. arvense)
4) triangular (deltoid) branch teeth vs. more attenuate

Here is a closeup of E. arvense to compare some of these characters: https://www.inaturalist.org/observations/25076244

Posted on 14 May, 2019 11:35 by stevendaniel stevendaniel | 1 comment | Leave a comment