Winter Corylus americana vs. cornuta working doc

The following is a working document (i.e. possibly updated with future study of these plants or feedback from others, which is very welcome as comments on this post or otherwise) on the winter identification of Corylus americana versus cornuta.

After casually observing these species, using the key on GoBotany ( https://gobotany.nativeplanttrust.org/dkey/Corylus/ ), and tossing my hands in the air on several plants I decided to dedicate a bit of time studying them closely in the hopes of gaining a greater understanding of these plants and distinguishing the two. Previously, I lamented the key for being somewhat misleading, and after some time in the field with plants I was fairly certain of species I have changed my opinion and think that the key is actually pretty good with one caveat; this is not a group where one looks at a single bud, or catkin, or branch and comes to a conclusion based on that. There is a bit of variability even within each plant, but by inspecting many buds, catkins, or otherwise it will be easy to get a sense of what most of that feature is like on this plant. Looking at one ID characteristic is generally consistent but as with many other things using a combination of features is probably best.

I didn't want to clog up the article with tons of pictures and have mostly provided aberrant examples, but I would encourage using the observations linked at the bottom of this journal post for examples of each feature and to get a sense of their variability.

Here are the key winter ID features and some thoughts around each, ordered from most to least reliable:

• Red glandular hairs: This is at the top of the list but admittedly it can be the most or least helpful feature. If you see even one on a plant -boom-, you're done, it's C. americana. No glandular hairs at first glance requires lots of careful inspection and likely reliance on other features to confirm species. Some C. americana plants are loaded with glandular hairs, while others have almost none. I have found the best place to search for these hairs to be in the near the axils at the terminal ends of branches (newest growth). These hairs will rub or fall off, and I think the extra cover from being in the crotch of branches and buds provides a bit of protection as seen in the photo below, where two can seen in front of the bud.

• Bud shape: Bud shape is seems to be very reliable. It doesn't seem to be uncommon to find a few buds on a plant that don't match up with the rest on a plant, but the vast majority will be the same. C. americana has round to blunt-tipped buds (> 90 degrees at tip), and cornuta has buds that are acutely pointed. One thing to note is that buds that are in flower seem to distort shape a bit, in particular it can make americana buds seem acute, as in the bud on the bottom right of the photo below. Note the top bud though, while pointed, is roughly 90 degrees or perhaps slightly greater. Most buds on the plants were more rounded than this and in most americana plants I studied the vast majority of the buds were notably not acute at the tips. Compare with the acute tips of cornuta in the second photo. Ironically, in cornuta flowering has just the opposite effect where it can make the buds seem oblong to rounded.

• Bud scales: This is a really nice ID characteristic not included in Haines' key but a friend told me was included in Woody Plants of the Northern Forest by Jerry Jenkins. In americana the buds have six or more scales, whereas in cornuta has about four. I have found that in most cases cornuta has glossy dark brown scales along the sides of the bud extending about halfway to the tip with the rest covered in lighter brown with white pubescence, giving the appearance that there are very few scales. americana often times it appears that the scales are encapsulating the entire bud but if not it's very easy to see multiple scales on each side of the bud. Flowering can distort the appearance of the buds slightly but number of scales should be consistent regardless. The photos above demonstrate these features nicely.
  
  
• Catkin (or "staminate aments" for those cooler botanists than I) peduncle length: In my limited experience, this seems to be the least reliable. The key states americana has catkin peduncle lengths of 1-5 mm, whereas cornuta is sessile to 1 mm. In my limited deep dive with these plants I have found several americana plants that had a catkin or two that appeared sessile, and several cornuta plants with catkin lengths > 1 mm. I think the utility in this one is that if you see a plant where the vast majority appear sessile it's probably safe to call it cornuta. Conversely, almost all long peduncles would suggest americana. In my experience (or perhaps I'm measuring it wrong) there seems to be a bit of overlap. cornuta peduncles can be sessile to 3 mm-ish, americana 2+ mm with the occasional aberrant short one. Overall though, one will gain a sense for what is short (cornuta) versus long (americana) with a little practice, and pair this with the next feature and you may be able to get a reasonable sense of which species from a distance to confirm with the other two features listed on the keys.

Here is an example of C. americana with sessile catkin:

And an example of C. cornuta with longer peduncle than expected:

Notes on other features:

Catkin length: Limited experience with this one, but it seems that the catkin length of C. americana is longer on average than C. cornuta. The C. americana plants I studied had catkins of 5 - nearly 10 cm, whereas C. cornuta catkins were generally 4 - 6 cm. Combined with catkin peduncle length americana catkins appear long and droop from the plants like grapes, whereas cornuta appears a bit more stout that often curve due to a short (or lack of a) peduncle. This, I suppose, is more of a spring feature when the catkins have opened up but felt it worthwhile to mention.

Non-glandular pubescence: Both species seem to be pretty variable with how dense the long, white hairs can be. Some plants have none, others have lots near the buds, and others still it is even more widespread. This can vary plant to plant or even branch to branch, but usually the hairs are mostly restricted to new growth.

Bark: I haven't noticed much of a difference between the two. Both have relatively smooth gray-purple or light brown bark that appears marbled with white in larger plants, the branches variably featuring indistinct lenticels (or lenticel-ish structures). In some plants I have found the older part of the plant is gray and younger light brown, and have found the opposite in others.

Final thoughts on ID and helpful documentation for iNat observations:

In summation, I think that reasonably careful study of these plants will provide a definitive identification in most cases. Often this can probably be achieved with a single feature, notably non-flowering buds or red glandular hairs if present, but if not a combination of several should get you there. As this relates back to iNat, posting clear photos of several buds (at least 5 but ideally 5-10) is probably sufficient enough for a sense of bud shape on most of the plant, and can easily be achieved by snapping a couple photos of branches that have multiple buds on them. If glandular hairs are present that is a 'gimme' so observations showing this are easy to confirm, although for plants where most have fallen off magnification using a loupe or otherwise might be required (and might be required to find them). Catkin peduncle length is helpful to include to support the other features, but probably would be difficult to confirm ID using that feature alone.

And, as with most things, expect to be thrown a curveball every once in a while like the observation here: https://www.inaturalist.org/observations/153471156 . Weird plants like this are what makes it fun!

Posted on 04 de abril de 2023, 06:26 PM by natemarchessault