Winter Tree ID Notes

Winter Tree ID Notes

Note:  These notes were designed to accompany a Keynote presentation, but they may be useful as a stand-alone review as well.

Title slide 1:  Most of the photos and examples here were taken within a few miles of my home--at the Ivy Creek Natural Area, along the Rivanna River, on sections of the Rivanna Trail, or as I walked the streets of town.  Many of you may recognize the site that's the background for this title slide:  Martin's Branch at Ivy Creek, on the way to the peninsula.  or many of us, tree identification is something we did in the fall or spring of the school year, when teachers gave us an assignment to go out and gather different leaves.  We did rubbings, or Scotch-taped the leaves to construction paper, and paged through tree guides looking for drawings or pictures of leaves to help us identify the trees.  

Winter wasn’t tree ID time.  Deciduous trees—those that shed their leaves when days grow colder and shorter--seemed unrelentingly gray-brown, indistinguishable from one another.  My camera has helped me see how indifferent and misleading that attitude was.

I originally took the photos that follow just because I loved what the camera revealed.  Over and over, I had a sensation you may have experienced as well—the feeling, in the words of a song, that  “I once was blind, but now I see.”   And as I accumulated pictures of those moments, I felt like sharing that feeling with other people who might be open to knowing and loving details of the lives of trees.

The word “lives” is important, because it reminds us that trees are our relatives--ancient relatives, but nonetheless, fellow beings with whom we share not only history but genes and DNA.  If we enter a woods or forest and feel that, in a deep and calming way, we are at home,  it’s because we are.  We are in our ancestral home, with distant cousins who are in fact acting as Earth’s stewards, quietly tending, cleansing, and nourishing the land, air, and water of the world. 

Most of the photos and examples here come from trees within a few miles of my home—at the Ivy Creek Natural Area, along the Rivanna River, on sections of the Rivanna Trail, or the streets of town.  Charlottesville is very much an “in-between” place, where northern and southern ecosystems meet, where the mountains meet the coastal plains, where urban sprawl meets old farmland, where homeowners introduce exotic species to a native landscape.  It is rich in species.  Last fall a neighbor and I, after walking a loop of a couple of blocks around our houses, put together a tour called “60 Trees in 60 Minutes,” where we had fun pointing out sixty different tree species in a fast-paced hour’s walk.

As all of that suggests, this presentation isn’t limited to native forest species.  Natives dominate, but I’ve also included trees growing out of their normal habitat, commonly-planted lawn and street trees, and exotic species often labeled “invasive.”  Most of you will encounter all of these, and I expect you will want to know them when you meet them.  

As a guide to specific trees, the presentation will probably work well in much of the eastern United States.  As a guide to terminology, techniques, and identification tools, it should have some value in an even wider area.  Once you begin to practice the kinds of observations that follow, you may find that identifying trees is actually easier when their leaves are off.  The absence of leaves enables us—maybe funnels us is a more accurate way of looking at it—to focus on other aspects of the tree, things that can be a unique signature. 

Slide 2:  if you have tried using a key to identify flowers or trees, you know that what makes identification so difficult is that almost everything is described with a range.  Within a species sizes vary, shapes vary, everything seems to vary.  

That’s frustrating, because we’re not used to looking at things that way.   The human-built world in our industrialized era is heavily biased toward standardization and uniformity.  We buy two by fours; nine by twelve rugs; six packs of beer; and car parts that fit our make, year, and model.  

The biological world is the opposite; it’s all about variability.  In fact, without that variability, there would be no biological world.  Genetic range within a species, and hybridization among species, are fundamental keys to survival.  A species has to be able to make do under a range of conditions and in different situations, or it will disappear.  Variation is its salvation.  But that variability can make the use of identification keys a hair-pulling adventure.  Instead of fighting that rich variety, though, consider loving it for what it signifies.

Slide 3:  Not only do trees—and most other living things—contain enormous variety within their species’ gene pool, but a number of them hybridize readily with other species of trees.  In fact, our whole concept of a “species” as something that doesn’t interbreed readily with another species—and when it does, produces sterile offspring—doesn’t work well at all with trees.  Here are some trees known for hybridizing frequently—and often producing fertile offspring as a result.

Loblolly, Longleaf, Shortleaf, Pond, and Pitch Pines hybridize with each other

Maples hybridize within the “hard” and “soft” groups--Red Maple with Silver Maple, for example

Many hickories hybridize, sometimes making hickory IDs a puzzle even for experts

In the white oak group, in some populations, different species share up to 50% of their genetic information.  Trees within the red oak group hybridize with each other as well.  The Missouri Department of Conservation says that Missouri is home to 19 species and at least 16 hybrids of oaks--that is, 16 crosses that occur so frequently that they are distinct and recognizable.

Slide 4:  Ash species readily hybridize (We have 16 species of ash across North America.)

Siberian Elm hybridizes with Slippery Elm 

Littleleaf Linden hybridizes with American Basswood and Large-leaved Linden 

The trees I’ve listed are just examples.  Numerous other species hybridize as well.  “Species” is a useful mental construct that we humans impose on an incredibly complex world.  It helps to keep a sense of humor and a sense of humility about expecting nature to conform to our expectations.

Slide 5:  I included this list of the most common trees in Virginia because it makes sense, when you’re trying to learn trees, to concentrate first on the ones you’re likely to see most often.  This list was compiled by the Virginia Department of Forestry; note that the trees listed are often a group of species rather than a single species. This way of counting grows out of the way trees are graded when buying and selling timber.  “White Oaks,” as listed here, doesn’t refer simply to Quercus alba, the species commonly known as White Oak, but to a whole cluster of related species, such as Chestnut Oak, Post Oak, Swamp White Oak, and so forth.  Gene Wengert, forum technical advisor on the Woodweb site, says there are twenty species of oak that fall into the red oak grouping!  

One other thing you might have noticed is that these 10 most common trees also happen to include a number that we just learned hybridize rather often.  

Slide 6:  Here is a quick guide to identifying some of these major species.

Oaks are alternate branching, with buds clustered on the ends of twigs.  Look for acorns beneath the tree. The pith of oak twigs is star-shaped in cross section.

Yellow Pines have 2 or 3 needles in each fascicle and most of them have a sharp prickle on the umbo of their cones.  (A fascicle is the little sheath wrapped around the base of the needles; it’s made up of bud scales.  The umbo is the part of the scale that you see when a cone is closed.)

Tulip Poplars have their seeds in distinct flower-like clusters that persist in the top of trees most of the winter.  They self-prune quickly, resulting in tall, clean, column-like trunks, and their twigs have valvate terminal buds. (More about that later.)

Maples are the only opposite-branching trees in the top 10; their twigs are slender, with each set of twigs and branches forming a “V” from the parent branch.

Slide 7:  Hickories have relatively thick twigs with large shield-shaped leaf scars; the husks that enclose their nuts split open into 4 parts 

Sweet Gum has numerous prickly mace-like balls dangling from the tree or lying beneath it.

White Pine has 5 thin, flexible needles per fascicle.  Its branches radiate from the trunk like the spokes of a wagon wheel. 

Slide 8:  Beech trees have smooth gray bark all their life.  Their leaves  persist all winter long on their juvenile growth; and the buds on their twigs are long, slender, wrapped in many scales, and sharply pointed.

Black Gum is distinctive with its short branches at right angle to the trunk and its blocky “alligator hide” bark.

Slide 9:  When trying to identify trees in winter, there are 7 places we commonly look for clues—the site where the tree is found, the tree’s branching pattern, its bark, its fruits, and its twigs, buds, and leaf scars.  Because of the limited time available, this presentation will focus on the last three items, which we can practice on indoors, and leave the first four to be covered in field trips.

Slide 10:  We’ll start with twigs.  It’s a good idea to begin with an overall impression of a twig—things like its color, thickness, pubescence, lenticels, and thorns.   Scales or wings, if present, are important features.  Don’t forget to check to see if there’s anything unusual about the pith.  A number of twigs also have a distinctive scent.  To check for scent, scratch the twig’s bark off in a small area with your thumbnail and then sniff the exposed part.

If you have the time, it’s good practice—and fun—to gather a few freshly clipped twigs at random and—without worrying about identifying them—try to describe 10 or 15 features of the twig, with the help of a hand lens.  That may seem challenging now, but by the end of the presentation, you should have the background to do that.

Slide 11:  Occasionally I’ll warn you of something you need to be careful about.  Here’s the first caution.  When considering the color of a twig’s bark, remember that it isn’t uniform.  It’s like pointing to a barn and asking what color it is, and having someone answer cautiously—and truthfully—”the side I can see is red.”  This year’s twigs are usually a lighter color than the older growth behind them on the branch.  In addition, the top of the twig, which is exposed to the sun, is often darker than the under part, which is shaded.

Slide 12:  When you’re first looking up into the canopy of a tree and trying to get some general idea of what it could be and couldn’t be, check the thickness and spacing of the twigs.  There are two rules of thumb to keep in mind about thickness.   

The first is that trees with large leaves or with compound leaves usually have thicker twigs to manage the additional weight and  withstand buffeting by the wind.  Catalpa and Paulownia are good examples of trees with large leaves and thick twigs; Ailanthus and Black Walnut are examples of trees with compound leaves and thick twigs.  

The second rule, which is useful when you have a twig in hand and are inspecting it, is that large leaves and compound leaves usually leave sizable leaf scars when they fall.

Slide 13:  The reverse of these two rules of thumb also applies.  Trees with small, simple leaves normally have thin twigs, and the leaves usually leave small scars on the twig when they fall.  Hackberry, Ironwood, and willows would be good examples.

Slide 14:  Let’s put those simple rules of thumb into practice.  What kinds of leaves do the following twigs bear?

Slide 15:  The twig on the left, which is obviously thick and has a large leaf scar, is from a Shagbark Hickory, which has compound leaves that can be up to fifteen inches long, almost always with five wide leaflets.  (The leaf scar is the large light colored patch in the middle of the twig and photo.)

The twig on the right, long and slender with a small leaf scar just at the base of the reddish bud is from an Ironwood (Carpinus caroliniana), which has a small, simple leaf.

Slide 16:  Here, the slender birch twig on the left--often called Black Birch or Sweet Birch--has small, simple leaves 2 to 4 inches long, while the thick Black Walnut twig with the large heart-shaped leaf scars has pinnately-compound leaves that can have 15 to 23 leaflets and grow up to two feet long.

Slide 17:  On the left is a Black Gum twig; Black Gum has a simple leaf a bit larger than the Ironwood and Black Birch--about 3 to 5 inches long, so its twig is a bit more stout; the Ailanthus or Tree of Heaven on the right has pinnately compound leaves that can have 11 to 41 leaflets, and grow up to three feet long!

Slide 18:  The Pecan on the left will have compound leaves a foot to a foot and a half long, with 9 to 15 leaflets.  The Black Willow on the right will have thin, simple leaves, 3 to 6 inches long.

Slide 19:  “Pubescence” is fuzziness or hairiness, and it’s much more common on leaves and twigs than most of us are aware of.  It’s often present when tender tree parts are most vulnerable to herbivores, and gradually wears off as they toughen and mature.  Pubescence is most likely to be found on this year’s twigs, although sometimes it extends farther back on a branch or stem.  Aside from discouraging herbivores from snacking on the tender new growth,  it also provides shade, on the one hand, and insulation against cold on another.

Slide 20:  This is Paper Mulberry, a non-native species whose fuzziness seems to be everywhere, and is so thick that the undersurfaces of leaves, the petioles of the leaves,  and the twigs themselves all have a velvety feel.

Slide 21:  Look how long the hairs are on this Staghorn Sumac twig!

Slide 22:  This densely woolen twig is from a Silver Linden.  Its scientific name is Tilia tomentosa, and the species name “tomentosa,” as you might guess, is Latin for “felt-like.”

Slide 23:  Mockernut Hickory is the most common of our hickories in the eastern U.S.  In older books you’ll often find its scientific name given as “tomentosa,” but in more recent times the name “alba,” for “white,” has been adopted. The undersides of the leaves are also covered with a dense mat of fine, short hairs.

Slide 24:  Sassafras twigs have bright green stems that stay as green twigs for several years, which is a big help in making a quick ID.  The twigs are often slightly pubescent when young.

Slide 25:  A Southern Red Oak twig.  As with most of the other pubescent twigs we’ve looked at, you will not always find pubescence on a Southern Red Oak twig.  Most often it will be on the newest part of the twig, especially on fast growing stems.  Leaves of the Southern Red Oak are also wooly below, and the terminal bud on the twig is pubescent.

Slide 26:  Winged Sumac—also sometimes called Shining Sumac.  This twig is so densely covered with hair that it looks as if it is covered with carpet!  The buds are also hairy, and the leaves, which are so shiny above, are a bit fuzzy below.

Slide 27:  Lenticels are another conspicuous feature of many twigs.  Lenticels are corky-looking spots or raised bumps on the surface of a twig’s bark.  They play an important role.  The green bark of twigs has chlorophyll and photosynthesizes just as leaves do.  To do that, it has to take in and discharge gases.  Lenticels are where that exchange takes place in bark, just as the stomates are where the exchange takes place in leaves.  Eventually the twig bark stops photosynthesizing and the lenticels are overgrown by bark.  The faster the bark is forming, the shorter the time lenticels last.  

Slide 28:  Some twigs with large, conspicuous lenticels that help in ID include 

Birches, Black Cherry, Elderberry, Honey Locust, Mimosa, Paulownia, Winged Sumac, and Zelkova.

Slide 29:  The red arrows point to lenticels on a Paulownia twig.

Slide 30:  Mimosa--often called Silk Tree.  Notice how raised and bumpy looking the lenticels are.

Slide 31:  Winged Sumac, with a rust-colored band across the middle of the white lenticels.

Slide 32:  A Zelkova twig, with lenticels roughening much of its surface.

Slide 33:  Thorns have a way of getting our attention!  Thorns, spines, and prickles are all hard structures with sharp, pointed ends, and they are all used by plants to protect themselves from herbivores.  We frequently lump them together as “thorns.”  But the three different names are used by botanists because each type is derived from a different plant organ.

Slide 34:  True thorns are modified branches or stems.  They have xylem and phloem tissue that is joined to the main vascular system in the tree trunk.  

Spines are modified, sharp-pointed stipules or leaves.

Prickles are outgrowths from the epidermis and don’t contain vascular tissue.

Slide 35:  A tree with true thorns, usually branched:  Honey Locust.

Slide 36:  Black Locust has spines rather than true thorns; the spines are actually modified stipules.  Notice that the spines, like stipules, flank a bud.

Slide 37:  A closer view of  Black Locust ‘s spines.

Slide 38:  This is a section of the ferocious Devil’s Walking Stick, sometimes called Hercules’ Club, with ring of prickles circling the stem.  Prickles are outgrowths of the epidermis and are not connected to the stem by vascular tissue.

Slide 39:  Trifoliate Orange with its long, vicious spines.  You know they’re spines because they’re originating at the base of the buds.

Slide 40:  An Osage Orange twig.  Again, the spine originates at the base of a bud.

Slide 41:  And one more tree bearing spines--a Hawthorn, again with the spine originating at a bud.  

Slide 42:  Callery Pear--the parent stock for Bradford Pears--with a thorn jutting out from the twig.

Slide 43:  Some trees and shrubs have other distinctive features to their bark.  Through a hand lens, you can see that Autumn Olive, as shown here, has silvery bark with red speckles.

Slide 44:  One uncommon feature of some species that provides a good start to an effort to identify them is the presence of “wings” on the twigs.  Species that often show wings include Sweet Gum, Winged Euonymus, Winged Elm, Bur Oak, and Blue Ash.  The presence of wings narrows the search down considerably, and since most of these trees don’t resemble each other otherwise, nailing down an identification should come easily.

Slide 45:  Winged Euonymus always makes me smile; it resembles something I would have made with TinkerToys when I was a boy.

Slide 46:  Not all Sweet Gum twigs are winged, but this cultivar shows the characteristic strongly.

Slide 47:  A Bur Oak twig, with the focus on a double-ridged wing.

Slide 48:  Think of the whole twig when trying to identify it—not just the outside.   The pith is the soft, spongy tissue at the center of young tree stems.  (As the tree grows and ages, pith is usually replaced, in large part, by xylem tissue.) Pith is made up of parenchyma cells, and it transports and stores nutrients.  As we shall see in slides that follow, the pith of twigs sometimes has distinctive features that aid in identification. 

Slide 49:  Three different kinds of pith are shown here, as if the twigs had been sliced lengthwise.  The first twig, on the left, has a continuous, unbroken pith.  This is by far the most common type.  In the middle twig, the spongy pith is interrupted by a series of tissues that look like diaphragms.  And in the third twig, on the right, the pith is divided into a series of nearly empty chambers.

Slide 50:  This photo of a Tree of Heaven twig shows its continuous buff-colored pith. 

Slide 51:  The pith of this Tulip Poplar twig is white, but the arrows point to a few of the diaphragms that regularly divide the pith.

Slide 52:  This Black Walnut twig has been sliced to reveal its unusual light-brown chambered pith.

Slide 53:  Butternut is sometimes called White Walnut.  It’s in the same genus as Black Walnut and also has a chambered pith, but as you can see, the pith is a darker brown.

Slide 54:  In this photo of a Paulownia twig, you see that the second year pith forms a hollow tube.  Paulownia twigs are also noticeably flattened at the nodes.

Slide 55:  It’s not just the structure of the pith that makes a good ID clue.  Color can also be valuable.  In most twigs, the pith of the new growth is white.  However, some trees have pith of a different color, which can be a good clue to their identity.  We’ve already seen that Ailanthus has a buff-colored pith; other species with colored piths include Kentucky Coffeetree, which is salmon-colored; Smoke Tree, which is orange; hickories, which are tan; and sumacs, which have a large orangish-tan pith ringed by brown. 

Slide 56:  Kentucky Coffeetree.

Slide 57:  Smoke Tree

Slide 58:  Staghorn Sumac

Slide 59:  Amur Cork Tree with pale beige pith, and distinctive neon green and yellow

layers beneath the bark.

Slide 60:  One other feature of pith to consider is its shape in a cross section.   Most twigs have a round continuous pith, but the pith of some trees takes a different shape.   Oaks and Sweet Gum have a star-shaped pith; hickories and poplars have a 5-sided pith; and alders have a more or less triangular pith.

Slide 61:  A Pin Oak twig, with star-shaped pith.

Slide 62:  Southern Red Oak, likewise with a star-shaped pith.

Slide 63:  Sweet Gum.

Slide 64:  Mockernut Hickory  It may take a little imagination to see the 5 sides!

Slide 65:  Taste and scent are other aspects that make some twigs distinctive.  We don’t have much of a vocabulary for describing these things, so we have to resort to comparisons.  Ailanthus, for instance, is often said to smell like rancid peanut butter.  Apple twigs are said to taste like licorice.  Black Birch smells like oil of wintergreen, and in fact was once a commercial source for it.  Black Cherry has an acrid, unpleasant, bitter almond smell.  Black Walnut has a strong oily medicinal smell which I like; other people might not.  Black Willow, like other willows, has a bitter aspirin taste, which is logical, since aspirin was originally derived from the salicylic acid in willow bark.  In fact, “salicylic” comes from the Latin name for the willow’s genus, Salix.   Magnolias have a mildly pleasant aroma.

Slide 66:  Ohio Buckeye has an unpleasant fetid odor.  A sniff of Sassafras or a chew of its twig will immediately make you think of root beer--for good reason, since Sassafras extract was originally the main flavoring agent in root beer.  Silver Maple has a slightly unpleasant odor.  Sourwood leaves have a sour taste, and a broken twig from the tree is said to smell like potatoes.  Spicebush has a strong, spicy scent that is sometimes described as slightly-lemon.  I can’t do any better, but that doesn’t match the scent very well.  And finally, Tulip Poplar (also known as Yellow Poplar) has a clean turpentine-like scent.

Slide 67:  That finishes our section on twigs.  Now we’ll take a look at their buds and scars.  Pictured here is a Yellow Buckeye twig with a portion of its large terminal bud, which is the name for the bud at the end of the twig.  You can see the large shield-shaped leaf scar, where last year’s leaf was attached before it fell off.  Within that broad scar you can see smaller, raised, light-colored scars where water and nutrients came into the leaf stem, and the photosynthesized products went out.  Down near the bottom of the photo you can see scars circling the twig where the scales from last year’s terminal bud were before they fell off.  Everything from those scars out to the end of the twig is the growth from last year.

Slide 68:  Sugar Maple has opposite leaves and branches, so these two lateral buds, or side buds, pictured are directly opposite each other.  Just below the base of the buds are leaf scars from the previous year.

Slide 69:  This Black Walnut bud has things we’ve seen in earlier slides--a terminal bud,  lateral buds, leaf scars and vascular bundle scars, but something new and rather unusual--superposed buds, or buds positioned directly above another bud.

Slide 70:  Key points to remember about buds and scars are these:

• Buds generate the leaves, flowers, and stem for the following growing season.
• Buds can be pointed, blunt, slender, globular, shiny, dull, smooth, pubescent, and many other things.  They come in a wide range of colors, have different scale patterns, and set on the twig at different angles.
• Leaf scars are unique for each species.

Slide 71:  If you can reach a twig, look at the buds, the bud scales, and the leaf scars.    The buds of most hardwoods are formed in late July,  and can be viewed from August to March or April.  Check first to see if the buds are opposite, alternate, or whorled.

Slide 72:  The twig on the left, a Green Ash, has opposite buds where its leaves will appear.  The Siberian Elm on the right has buds that are alternating as they wind their way around the stem in a Fibonacci ratio.

Slide 73:  This Catalpa twig has three leaf scars at each node, but it’s not possible to get all three in a photo at one time and still show what the leaf scars look like.

Slide 74:  So many trees have alternate buds that an alternate pattern is not of much help with identifying their twigs.  But opposite buds are uncommon enough that they can be quite helpful in narrowing down an identification.  I use the phrase “MAD horse bucking violently” as a mnemonic device to help me remember the most important opposite-leaved trees.  “MAD” stands for maple, ash, and dogwood.  “Horse”stands for Horse Chestnut (which is actually a buckeye,” and “Bucking” stands for the rest of the buckeyes.  “Violently” stands for the viburnums. 

Slide 75:  Here are a dozen trees with opposite buds, including both native and exotic species:  

1. Ashes
2. Buckeyes
3. Dogwoods
4. Eucalyptus (juvenile)
5. Fringetree
6. Katsura
7. Maples
8. Olives
9. Paper Mulberry
10. 10.Paulownia
11. 11.Viburnums

Slide 76:  Now for a closer look at some of these trees with opposite buds; this is Japanese Maple, an enormously popular tree in urban landscaping.

Slide 77:  Red Buckeye is a lovely small tree that deserves to be more widely planted.

Slide 78:  Kousa Dogwood is another popular landscape tree, used more frequently now because of its resistance to the anthracnose that has been killing our native Flowering Dogwoods.

Slide 79:  Paper Mulberry, which is invasive in some locales.

Slide 80:  Paulownia.  Notice how small the buds are, for a tree with such mammoth leaves!

Slide 81:  Katsura.  What beautiful color on these buds!

Slide 82:  We’ve been looking at lateral buds.  Let’s take a look now at terminal buds, which are the buds at the end of a twig.

Slide 83:  Buckeyes have the largest buds of any of our native trees.  This is a Yellow Buckeye ~ Aesculus flava.

Slide 84:  Sweet Gum.

Slide 85:  Not all tree species form a terminal bud.  In some, the twig keeps growing until days shorten and the food supply dwindles.  Then the twig dies back to the last lateral bud, which becomes a “false” terminal bud.  Since the false terminal bud starts the next year’s growth off at an angle, twigs of such trees come to have a zigzag appearance.

Slide 86:  How do you know whether the bud at the end of a twig is a true terminal bud or a false terminal bud?  Use a hand lens to look closely at the scar next to the bud.  If it is a false terminal bud, what you will see is a “twig scar” rather than a “leaf scar.”  The twig scar will have no vascular bundle scars, and it will have concentric circles marking where the pith, wood, and bark were.

Slide 87:  Some familiar trees that have false terminal buds include: 

1. Aspen
2. Basswood
3. Birches
4. Elms
5. Goldenrain Tree
6. Hackberry
7. Ironwood (Carpinus caroliniana) 
8. Ironwood (Ostrya virginiana)
9. Red Mulberry
10. 10.Sycamore
11. 11.Tree of Heaven

Slide 88:  Here is a photo of a Basswood twig and its false terminal bud.  As you can see, the bud isn’t really growing directly out of the end of the twig, but instead is growing out of the side of the twig and jutting forward.

Slide 89:  Another twig with a false terminal bud--this one American Elm.

Slide 90:  As I mentioned early in the presentation, one of the ways to single out oaks is to check out the ends of twigs for multiple buds in a cluster.

Slide 91:  Here are three different oak species--two from the white oak group and one from the red oak group--showing how buds are crowded together at the end of the twig.

Slide 92:  You may already have noticed that buds can come in a surprising array of colors.  Here is a sampler of five species, with no two coming close to resembling each other.  The mustard yellow buds are on a Bitternut Hickory; the dark brown buds are on a Green Ash; the dark red buds are on a Zelkova; the lemon yellow on a Great Rhododendron; and the cherry red on a Southern Red Oak.

Slide 93:  This large Horsechestnut bud--only the bottom part of which you see on the right side of the photo--is notable not for its color but for its resinous coating. 

Slide 94:  Let’s turn our attention now to the scales which are wrapped around the buds, which may contain stems, leaves, flowers, or a combination.   Bud scales are actually very tiny, very tough modified leaves.  They enclose and protect developing parts of the bud from insects and from freezing cold.  The arrangement of these scales around the bud differs for different species.

Slide 95:  This Southern Magnolia shows only a single scale, which wraps completely around the terminal bud.

Slide 96:  Willows have a single bud scale; this one is the familiar Weeping Willow.

Slide 97:  Tulip Poplar buds are covered by two scales that come together in a valvate arrangement often compared to a duck’s bill.

Slide 98:  American Basswood also has two scales, but instead of meeting halfway like the Tulip Poplar, one of these scales overlaps the other, causing the buds to have a humped, lopsided appearance.

Slide 99:  These Sawtooth Oak buds have what are called “imbricate scales,” numerous scales that overlap like roofing tiles.

Slide 100:  These Ironwood scales—Ostrya virginiana—are imbricate as well, but they have a couple of other distinctive features.  One is the fine grooves in the scales, and another is the bands of color on each scale.  (Note:  Ostrya virginiana is the “Ironwood” with shaggy, flaky bark; Carpinus caroliniana is the one with smooth gray bark that is also called “Musclewood.”)

Slide 101:  This Witch Hazel has what are called “naked buds.”  Instead of being protected by scales, they insulate themselves with a thick fuzzy coating.

Slide 102:  Let’s try a self quiz now.  What kind of scale pattern does this Black Birch have?

Slide 103:  Here’s another look at the Sweet Gum bud we saw earlier.  Notice that it has imbricate scales as well.

Slide 104:  Typically, once a bud opens, its scales drop off.  When they do, they leave a series of horizontal scars on the surface of the growing stem.  These are called “bud scale scars.”

Slide 105:  This photo of a Sweet Gum twig shows the bands of bud scale scars circling the twig.  Each set of bands marks where a terminal bud once grew, so the space between each pair of bands tells us how much the twig grew in a given year.

Slide 106:  We have looked at terminal buds.  Now we’ll take a look at lateral buds.  Lateral buds are found on the side of a twig.  Trees readily identified by their lateral buds include:

Slide 107:  Beech, which has long, pointed, scaled buds 

Slide 108:  Kentucky Coffeetree, which has sunken, wooly buds

Slide 109:  and Elm, whose buds sit off-center over the leaf scar.  This is and American Elm...

Slide 110: and this is Siberian Elm, in which the buds are really off-center.

Slide 111:  A relatively small number of trees and shrubs have stalked buds.   Among these are:

• Striped Maple
• Red Maple
• Eastern Redbud
• Black Alder
• White Alder
• Bitternut Hickory
• Persian Parrotia
• Cranberry Bush

Slide 112:  Here is a Striped Maple twig with its stalked buds.  If you look closely at the bud on the right, you can see that the bud is valvate, like the Tulip Poplar we saw earlier.

Slide 113:  These Eastern Redbud buds are stalked as well.  If you look at the one at the top in particular, you can see that the buds are imbricate.

Slide 114:  Another aspect of buds that can be useful in identification is the angle which a tree’s buds usually form with the stem.  Trees with buds at a 45 degree angle, for instance, include American Chestnut, Ironwood (Ostrya virginiana), and Zelkova.

Slide 115:  American Chestnut...

Slide 116:  Japanese Zelkova.

Slide 117:  Some buds are angled so severely that they lie flat against the stem, or are pressed closely against it.  They are referred to as “appressed” buds.  A number of trees show this trait, including: 

• Apple
• Blackhaw
• Box Elder
• Bur Oak 
• Elms
• Chinkapin Oak
• Eastern Redbud
• Hackberry
• Lombardy Poplar
• Persimmon
• Serviceberry
• White Mulberry
• Willows

Slide 118:  This Apple twig is an excellent example.  Look how closely the bud hugs the twig.

Slide 119:  Box Elder...which is actually a maple.  You probably noticed the opposite buds right away.

Slide 120:  A slender Hackberry twig, with appressed buds.

Slide 121:  Lombardy Poplar buds, pressed tightly against the slender, glossy stem.

Slide 122:  One more example of appressed buds: these lovely, graceful Serviceberry buds arching into their stem.

Slide 123:  Now for an unusual set of buds.  The unusual thing about them is that you can’t see them!  They’re called “immersed buds,” and they are hidden within the base of the petiole (leaf stalk) as long as leaves are on the tree.  When the leaf falls off, the bud is finally exposed.  Because the petiole completely surrounded the bud, the leaf scar that remains completely encircles the bud.  Trees with immersed lateral buds include:

• Black Locust
• Honey Locust
• Staghorn Sumac
• Sycamore
• Yellowwood

Slide 124:  Here are two photos of a Sycamore twig.  The one on the left shows the leaf still attached to the twig.  The red part standing up is the petiole or stem of the leaf; look how it widens at the base.  The photo on the right shows the same twig after I broke off the leaf to reveal the tender bud hidden inside the base of the petiole.

Slide 125:  The photo on the left shows the base of the petiole of the leaf I broke off.  Notice the eight or so greenish circles around the rim of the base; those are the vascular bundles that supply the leaf with water and nutrients for photosynthesis and carry out the sugars manufactured during photosynthesis.  

In the photo on the right, you can see those vascular bundles in the leaf scar that rims the bud.  Here the leaf scar has dried and sealed itself off, and the vascular bundles have plugged themselves with a cork-like substance.

Slide 126:  This is a Yellowwood twig.  Notice how the yellow petiole at the top of the picture widens at its base.

Slide 127:  Again, on the left you can see the base of the petiole after I broke off the Yellowwood leaf.  And on the right you can see the remaining leaf scar encircling the bud.  The small, dark green ovals within the leaf scar are the vascular bundles.

Slide 128:  A Staghorn Sumac twig, with its once-concealed bud now revealed.  See how the leaf scar wraps all around the bud?

Slide 129:  To sum up what we’ve learned now about leaf scars:  They are the marks left on a stem or twig when its leaves are detached.  Within each leaf scar are one or more smaller scars, called vascular bundle scars, which are the stopped-up remnants of the tissues that transported liquids into and out of the leaf.

Slide 130:  This odd-looking picture shows an Ailanthus leaf attached to a stem.  Look how firmly it is attached, and how it is buttressed for strength as it shelters the bud within the arc formed by the petiole’s base.

Slide 131:  You can see the base of the Ailanthus’s petiole on the left, and the leaf scar with its vascular bundles on the right.

Slide 132:  This is a Box Elder twig; I removed the leaf on the left hand side just before taking the picture, while the leaf on the right is still intact.  The leaf scar on the left is still fresh and green.

Slide 133:  White Ash and Green Ash are difficult to tell apart.  Often people go by the site where they find the tree:  Green Ash typically grows near rivers and streams, in floodplains or even swamps, while White Ash is typically an upland species.  If you compare twigs, you may be able to distinguish them by the different ways the buds are placed above the leaf scars, as shown here.

Slide 134:  This Butternut twig shows a unique trait--a “mustache” growing above the leaf scar, below the bud.

Slide 135:  A distinctive feature of some tree  species is that their leaf scars, instead of being flush with the surface of the twig, are raised noticeably from the twig, and sit on a kind of hump.

Slide 136:  White Mulberry, shown here, is a good example.

Slide 137:  Other features of twigs that can be helpful in identification are the number of vascular bundle scars in the leaf scar, and sometimes the pattern they create.

• Autumn Olive, Persimmon, and Sassafras all have a single bundle scar.
• Maples,  Poplars, Willows, Dogwoods, Sweet Gum, Black Gum, and Mimosa have three bundle scars.
• Ashes and Sourwood have numerous bundle scars forming a “U.”
• Ailanthus has 8 or 9 large, prominent bundle scars.
• Oaks have numerous scattered bundle scars.

Slide 138:  Autumn Olive, with its single bundle scar--sometimes called a “bundle trace.”

Slide 139:  A very clear photo of the 3 vascular bundle scars within this Red Maple’s leaf scar.

Slide 140:  Another maple, this one a Norway Maple.

Slide 141:  Lombardy Poplar.

Slide 142:  Sweet Gum.

Slide 143:  Mimosa.

Slide 144:  White Ash, with its vascular bundles forming a U shape below the bud.

Slide 145:  Shumard Oak, with numerous dark vascular bundles scattered around the light-colored leaf scar.

Slide 146:  Bur Oak, with many small light-colored bundle scars packed into the leaf scar.

Slide 147:  Some trees have small leaf-like structures attached to the stem on each side of the petiole.  They are actually modified leaves, and they are called stipules.  Like leaves, they leave a scar when they are gone.  They most commonly come in pairs.

Slide 148:  The original function of stipules is unknown, but the best guess is that they shelter the bud and protect the emerging leaf.  In many species they shrivel up and die not long after the leaf completes its growth.  In others, they may actually persist up until or past the time the leaf falls.

Slide 149:  Some stipules, such as those of Magnolias, Tulip Poplar, Beech, and Sycamore, entirely encircle the twig.

Slide 150:  These stipules, the lively green structures circling the stem of a Sycamore, resemble a fanciful umbrella.

Slide 151:  The arrow shows the scar left when a Sycamore stipule drops off.

Slide 152:  The red arrows point to a couple of the stipule scars on a Tulip Poplar twig (which you no doubt recognized because of the valvate “duck bill” bud scales).

Slide 153:  Stipule scars on a Southern Magnolia twig.

Slide 154:  And on a Saucer Magnolia.  (Look at those furry buds!)

Slide 155:  Yet another magnolia--this one Sweet Bay Magnolia.

Slide 156:  Not all stipules circle the twig by any means; the curved stipule scar here on this Lombardy Poplar looks like the hair on a child’s drawing of a girl wearing a hat.

Slide 157:  The stipule scar on this American Basswood is crescent-shaped.

Slide 158:  I enjoyed creating this presentation.  I hope it has added something to your love and understanding of trees!

Slide 159:  The End.