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 April 04, 2023 06:26 PM by natemarchessault natemarchessault

Observations

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

March 31, 2023 01:01 PM EDT

Description

Most buds appeared acute at the tip, scanned many lengths of branches and no red glandular hairs were found. The peduncles to the catkins, however, appeared to be > 1 mm which according to Haines would indicate americana. Am I measuring this wrong? Also there were several weird double- and triple-catkins.

Photos / Sounds

What

American Hazelnut (Corylus americana)

Observer

natemarchessault

Date

April 3, 2023 01:18 PM EDT

Description

These were easy, this patch had branches dense with red glandular hairs. Buds were almost all round/obtuse, longish peduncles to catkins, the catkins themselves seeming longer than cornuta (many were 6-10 cm). Interestingly, at this spot it appeared that there were large patches cornuta on the left side of the trail and americana on the right, shown in the last photo.

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 3, 2023 01:18 PM EDT

Description

I think a strong argument can be made for this patch being cornuta, on The Knob which has abundant C. americana. It was interesting that these were growing abundant on the left side of the trail while americana was abundant on the right.

The vast majority of the buds were notably acute with only a few here and there that could be considered obtuse. No red glandular hairs were found even in the prime places to find them when most have fallen/rubbed off. The peduncles to the catkins were virtually nonexistent, the catkins themselves short (2-4 cm) although perhaps not fully formed. Not an ID feature but noted that almost all of the catkins in this patch were in 2's (I wonder the cause of this?).

Photos / Sounds

What

American Hazelnut (Corylus americana)

Observer

natemarchessault

Date

April 3, 2023 12:59 PM EDT

Description

Buds rounded to obtuse, this plant had sparse glandular hairs, peduncles to catkins a few mm in length, catkins 5-8 cm. This plant had a four catkin cluster! Bark a dull grayish, to lighter brown at younger growth.

Photos / Sounds

What

American Hazelnut (Corylus americana)

Observer

natemarchessault

Date

April 3, 2023 12:56 PM EDT

Description

Most buds rounded to obtuse but as can be seen in the bottom bud in the third photo some can appear acute, which for some may be influenced by flowering. Some areas with lots of red glandular hairs while other terminal branches lacking any. One thing I noticed when observing this patch was that the best place to hunt for persistent glandular hairs was near the axils in as new growth as possible as shown in the 5th photo. It may be hard to see but there are a few red glandular hairs in front of the bud. I think being in the crotch of branches/buds provides a bit of shelter helps to keep them from falling off. Most catkins long, 5-9 cm.

Photos / Sounds

What

American Hazelnut (Corylus americana)

Observer

natemarchessault

Date

April 3, 2023 12:45 PM EDT

Description

This plant had many areas without red stipitate glands, as well as a catkin or two which appeared essentially sessile. The lower portion of this plant was a warm brown which transitioned to gray at the upper parts

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 4, 2023 12:34 PM EDT

Description

Acute buds, short catkins on short peduncles, no glandular hairs seen. Female flowers present but male catkins still dormant on this plant.

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 4, 2023 12:43 PM EDT

Description

Buds acute; note the second and third photos are not pointed but are still acute. Catkins 3-4 mm borne on short pedicels, note how they arch off the branches rather than hanging straight down as is common in americana. Flowers not all that useful in ID but hard not to appreciate.

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 4, 2023 12:50 PM EDT

Description

Acutely-tipped buds, catkins 3-5 mm on short peduncles. These peduncles were on the long side for this species but noted still a slight arch to most catkins. Branchlets very fuzzy at terminal end in this individual.

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 4, 2023 12:57 PM EDT

Description

Most buds acutely-tipped, note the third photo where a bud is a bit rounded. Catkins 3 or so cm with short peduncles, probably not fully opened yet.

Photos / Sounds

What

Beaked Hazelnut (Corylus cornuta)

Observer

natemarchessault

Date

April 4, 2023 01:00 PM EDT

Description

Buds mostly acute, note in the second photo how flowering has the opposite effect as it does in americana and the bud appears rounded (in americana flowering budd can look acute which, ironically, for both species would suggest the other). Catkins 3-4 cm on short peduncles.

Comments

Thanks, Nate! Excellent deep dive into Corylus. I, for one, really appreciate the work you've put into photographing, describing, and pinning down the nuances and variations found in these two species. Very helpful!

Posted by margaretcurtin 11 months ago

Thanks @margaretcurtin ! Little projects like this are fun and I enjoy becoming intimately familiar with species that can be difficult to distinguish. I hope to do more in the future!

Posted by natemarchessault 11 months ago

Very helpful! Much appreciated.

Posted by tsn 11 months ago

Thank you @tsn !

Posted by natemarchessault 11 months ago

Nicely done. You could add markups on the second photo (circles and arrows) to make that combo photo more clear. Italicizing sci names throughout would be good. Jerry Jenkins is a very observant naturalist, so I'm not surprised to hear he had that one tip. His Northern Forest Atlas images are great.

Posted by wernerehl 11 months ago

@wernerehl thanks Bob! I've made the changes you've suggested to the doc.

Posted by natemarchessault 11 months ago

Wow, yes, looks really great!

Posted by wernerehl 11 months ago

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