Tuesday, February 15, 2011

Care to Learn Your Carya's (Hickories)?

Trees have always been one of my favorite pieces to the puzzle we call Nature.  The list of their functions and uses in both the natural world and our human society is miles long.  From recycling our waste carbon dioxide into breathable oxygen to supplying the world of birds and beasts food of countless varieties; it's safe to say the more trees, the better off our world is.  When I first started off learning my trees it was at the basic level of identifying it down to genus.  I could identify Oaks from Maples and Ashes from Pines.  Little did I know just how diverse and unique Ohio's forests were as I hiked through them in my earlier years.  In Ohio there are over 150 species of native trees and shrubs that grace our landscape and today I would like to show you how to identify a particular genus of native trees in their winter state.

Winter twigs of Ohio's indigenous Hickory species

Meet the genus Carya, commonly known as the Hickories.  Hailing from the Walnut (Juglandaceae) family there are six species native to our state: (from left to right) Shellbark Hickory (C. laciniosa), Bitternut Hickory (C. cordiformis), Pignut Hickory (C. glabra), Mockernut Hickory (C. tomentosa) and Shagbark Hickory (C. ovata).  There is a sixth species native, Red Hickory (C. ovalis) also known as Sweet Pignut Hickory that was long considered a variety of C. glabra but was recently designated as a separate species.  With that being said let's take an inside look at each individual species and how to identify it down to species in the field.

SHELLBARK HICKORY (Carya laciniosa)

Shellbark Hickory bark
Shellbark Hickory bud

Also known as Kingnut Hickory, this large tree grows throughout the state but is the most habitat restricted species of Hickory we have.  Found in wet bottomland and floodplain forests along streams and rivers as well as terraces and lower slopes in valleys, C. laciniosa is rarely found growing anywhere else.  As you will see later in this post, the mature bark can be easily confused with the more or less identical bark of another hickory, the Shagbark.  The best way to determine the two species in winter is by taking a look at the twigs.  Even though Sharbarks tend to grow on the higher and drier areas of the forest, I have seen them grow side by side Shellbarks in a bottomland forest on several occasions.  Shellbark Hickory twigs are a light orangish-tan color, stout and almost always glabrous (smooth, without hairs) while Shagbark twigs are darker brown colored, not typically as thick and quite hairy. While obviously not noticeable during the winter months, Shellbarks almost always have 7 leaflets per leaf versus the typical 5 on Shagbarks.  This acts as an easy separator during the growing season.

Twig with rachis
Typical form of the tree

Another helpful way to distinguish the two shaggy barked hickories is the presence of the rachis' over-wintering on the twigs, especially on younger trees.  The rachis is the long 'stem' that each leaflet (single, small 'leaf') attaches to to complete one, single hickory leaf.  In Shellbark's case just the leaflets tend to fall instead of the whole leaf; rachis and all, as seen in the picture above on the left.  C. laciniosa  tends to grow tall and straight with a round crown of thick, stubby branches on top.  These large trees can attain heights of over 100' tall and over 3 feet in diameter in the right conditions.  In fact, I have seen an old-growth shellbark growing in a wet flatwoods in southwestern Indiana that was approaching 150 feet in height with no branches for the first 80+ feet!


Shagbark Hickory bark
Shagbark Hickory bud

Up next to help dilute the confusion between the two is Shagbark Hickory.  In the picture above you can see the bark is the same as the aforementioned Shellbark Hickory in that the mature bark splits and begins to peel away from the trunk in long, curved strips.  Doing well in the moist soils of valleys and bottomlands to the dry upper slopes and ridge tops, C. ovata can be found growing in just about any part of a deciduous forest.  As previously mentioned, the twigs of the Shagbark are a dark brown and hairy with a pinkish terminal bud that is flanked by darker, purplish bud scales.  This is one of most commonly found hickories, occurring in every county in Ohio.   The new-growth twigs on this hickory tend to be rather hairy and noticeably darker and not as stout as the Shellbark.

Young bark of Shagbark
Typical crown form

The bark of younger Shagbarks is slow to get peeling and stays tight against the tree until small fissures form as cracks up and down the truck as seen in the picture on the left.  Given time these trees will grow to have the same pattern and shape as the Shellbark Hickory.  I've seen where some people take the long strips of bark from Shagbark hickories and boil them down to make Hickory syrup.  It's not as sweet as Maple syrup but is said to have a unique, smokey taste all its own.  I'd love to give it a try sometime whenever given the chance.

BITTERNUT HICKORY (Carya cordiformis)

Bitternut Hickory
Bitternut Hickory bark

Next is the first of the three 'tight bark' hickories and probably one of, if not the easiest tree to identify in Ohio when you can take a look at the buds on the twig.  Bitternut Hickory (C. cordiformis) has very smooth, thin and light grey colored twigs that are adorned with sulfur-yellow, naked buds unlike any other tree or shrub inside our state.  All the other hickories have scaled buds which have different layers or coats of 'shells' on the bud however C. cordiformis's bud has no layered or peeling scales.  The number of leaflets can range from 7-11 per leaf but seem to regularly average 9 in our state.  The individual leaflets also have a tendency to be the most lanceolate and thin.  The bark is thinly furrowed and does not peel or appear shaggy at all.  Towards the base of the trunk the bark almost looks as though a vandal with a spray can gave the bark a thin, silvery and shiny coat of paint. 

Bitternut twig and buds
Bitternut bud

On the left is a close-up, macro shot of the bud to show just how unique and alien it really looks.  The smooth twigs are covered in small, light colored 'dots' called lenticels.  A lenticels job is to act as a pore for the twig and tree and allow gas (mostly CO2 and oxygen) to move in and out of the plant.  Most commonly found growing in moist soils and on lower slopes, Bitternuts can really be found growing throughout a forests topography.  It is another very common tree found in every area of Ohio.  It gets its name from the small, inedible hickory nuts it produces each season.  While most hickory nuts are very palatable and tasty the Bitternuts, as the name suggests, are very bitter and are largely left alone by wildlife except in the most desperate of situations.  Like the rest of the hickory species this tree can attain great size and serve as a dominant member of the forest canopy.  

Old growth Bitternut
Blogger and old growth Bitternut

On my family's farm in Clark county, Ohio there is a small woodland patch that has several old-growth Bitternut Hickories that are over 150 years of age.  The above pictures show the largest one in summer as well as your blogger standing next to it in its dormant, winter state.  Over 100' tall (I've measured the tallest at 115') and approaching 4 feet in diameter, these behemoths show just how large this relatively slow growing tree can get when given the time and resources.

MOCKERNUT HICKORY (Carya tomentosa)

Mockernut bark
Mockernut twig and bud

Mockernut Hickory (C. tomentosa) gets its latin scientific epithet from the word 'tomentose' which means covered in dense hairs, which describes the twig and buds pretty accurately.  The twigs are brown in color and have a pretty hairy feel and look to them especially towards the the end of twig (new growth).  The terminal bud (bud at the end of the twig) is another way to tell this species apart.  The buds light yellow in color and have a "hershey kiss" look to them or to me look like a pear sitting upright.  During the growing season the leaflets number from 7 to 9 but are predominately 7.  The undersides of the leaves and rachis is very hairy.  The bark is similar to that of C. cordiformis, as it is silver-grey in color and is tight against the tree with no peeling or shedding.  Found growing usually on the higher slopes and well drained ridges, Mockernut is predominantly found in the eastern half of our state.

Typically growth form and habit
Young Mockernut bark

If confused by the bark and a twig is not reachable the best way to determine this from a Bitternut Hickory is to take a look at the crown of branches and twigs.  Bitternut branches tend to be long and thin with the ends coming to a point that appear to have no bud while Mockernut's branches a shorter, more stout and thick and end with a fat, round bud at the end.  Once you get to know your trees better it becomes easier to distinguish the bark between C. cordiformis and C. tomentosa without having to look at the other features, but when in doubt look up.  The bark of young Mockernuts can be confused with the young bark of Shagbarks (before any peeling/fissuring) and even more so with Bitternuts.  Once again, looking at the twigs and buds can help rule out the other species.

PIGNUT HICKORY (Carya glabra)

Pignut growth habit and form
Pignut twig and bud

The final species of hickory to be identified is the Pignut Hickory (Carya glabra).  The latin scientific epithet for this tree is just the opposite of the Mockernut.  Glabra comes from the word 'glabrous' which means smooth and without hairs.  This is describing the twig of this hickory species which is dark brown, smooth and on average the thinnest.  The buds are scaled and can look like miniature, hairless versions of their Shagbark counterpart.  The leaflets are almost always 5 in number and have a slender, glabrous rachis much like the twig.  Most commonly found on the drier soils of the upper slopes in the forest community, C. glabra can, like many of the other hickories previously discussed, occur in other habitats where the soils are well-drained.  The range within Ohio is very similar to that of the Mockernut Hickory in the fact it resides in the eastern half of the state with a few disjunct populations in the northwestern section.

Typical Pignut bark
Shaggier bark (perhaps Red Hickory variety)

Pignut Hickory has the unique pleasure in the Ohio hickories of being in the middle between loose-barked and tight-barked trees.  On the right is a mature Pignut that has small pieces of bark slightly peeling away from the tree.  If confused on whether or not the tree is a Pignut or Shagbark/Shellbark remember that the twigs on the Pignut are thin and the buds small, while the Shag and Shellbark are stout and large.  A simple look up into the canopy should do the trick to resolve this problem in the field.  The picture on the left is of a Pignut with a considerable amount more bark peeling away from the trunk.   I have read and observed that the closely related Red Hickory's (C. ovalis) bark is slightly more shaggy than that of the average Pignut while the twigs are mostly the same with perhaps C. ovalis's being a bit more stout.  I suspect due to the shaggier appearance of the specimen pictured on the left that it is a Red Hickory rather than a Pignut.  If the leaves were present it would go a ways in helping to I.D. this tree as C. ovalis has 7 leaflets per rachis while C. glabra only has 5.

To wrap things up let's come back to the first picture I posted with all five species twigs represented in a line up.  I didn't line these up in just any random order but in regards to where you will most likely (key word being likely) find them in regards to where you are topographically in the forest community.  When looking at a hickory tree species it is helpful to notice where you are on the aspect of the slope to help rule out or tie in which species to consider.

Shellbark, Bitternut, Pignut, Mockernut and Shagbark

The Shellbark starts things off in the bottomlands and at the lowest points.  Bitternut is next up and is found in the bottomlands as well the lower, more moist slopes.  As you go farther up Pignut can be found from the lower slopes up to the higher ridges.  Mockernut sticks to the higher slopes and ridge tops while Shagbark dominates the highest and usually driest areas.  Remember that the trees don't read the books and this is only a guideline for the most typical situation but has provided to be an important resource in the past.

Well I hope you walk away from this post more confident in your abilities to correctly I.D. our hickories in their hibernative, winter state.  I plan on doing other posts in the future breaking down more families and genus' of our native trees. 


  1. Thanks for putting all those photo together. Winter is a great time to study trees, and this is an interesting family!

  2. Haha Dave always reminded me that trees don't read book when we worked together over the summer. Cool way to use the last slide in relation to topography.

  3. Really good stuff, Andrew! I think you're correct that the photo on the left above is C. ovalis, which is more a bit more "shaggy". They seem to have larger buds on average, and commonly 7 leaflets on the larger trees. Now that it's considered to be separate from C. glabra, maybe we should start teaching it. But hickories are already tough for our students! I'll be refering them to your treatment here, thanks!

  4. Thanks a million, Bob! Coming from the man himself who helped me learn these very trees and become genuinely interested in them sure means a lot to me!

  5. Came on this hickory post while looking for your Puttyroot photos to share with my sister who had just taken pictures that I thought were of Puttyroot leaves. I have been struggling this winter with the identification of Pignut and Sweet Pignut here in NY. We have both. Trees I have always called C. glabra with five leaflets and nuts of what seems the typical pignut shape are oval in cross-section. The nuts I find under the trees with the bark with deeper fissures have very round nuts. My dendrology text, Harlow and Harrar, shows C. ovalis with a oval vertical cross-section, not round as I am finding. I presume the scientific name comes from this cross-section shape.? I'll count leaflets come summer.

  6. I cannot thank you enough for posting this blog!! It's exactly what I wanted! I have a wooded piece of property in SE Illinois and do quite a bit of conservation work on it in the winter. I could identify hickories from other tree species, but I could not tell you what type of hickory it was. I now have a fighting chance at identifying exactly what type of hickory a particular hickory is. Thanks again!!

  7. Andrew, thank you posting this outstanding resource. I've looked at it often and now am quite adept at distinguishing between the bitternut, shagbark and shellbark we have on our SW OH farm. As you said, the trees--or the squirrels--don't read the books; we have several shellbark growing on the highground right next to the shagbark, as well as shag next to shell in the bottoms. Hats off to you sir for this guide.