Aspen and poplar - what's in a name?

What's in a name? Plants are named by way of binomial nomenclature - a first and last name - expressed as Genus species or Genus species. If John Smith were a plant, for example, its name would be Smith john, either in italics or underlined to give the reader a heads-up on its taxonomic status.

This binomial nomenclature can be referred to as a scientific, technical, or Latin name but I recently came across the term botanical name which makes the most sense for me. Scientific or technical seem daunting to the lay person, and Latin may or may not be accurate since it may be a variation of a Latin word, a Greek word, or something Latinized from Greek. So, botanical name is the term for me since it's a botanical specimen that I'll be discussing. Binomial nomenclature is used for animals, too, so I'll have to think about that.

Plants may also go by a number of common names, some of which they might share with another plant or two. Trees in the Populus genus go by poplar and aspen, for example. While multiple or shared common names can lead to some confusion when attempting to discuss a tree, the botanical name gets you directly to the species of interest. The Forest Trees of Maine describes three Populus species: P. tremuloides, P. grandidentata, and P. balsamifera. You may find others that have been planted in parks or urban developed areas but if you learn these three, you'll be well on your way to recognizing other trees in this genus and distinguishing them from the Maine forest tree species.

P. tremuloides and P. grandidentata go by the common name aspen and have some similarities that distinguish them from P. balsamifera which goes by the common name poplar. See the chart below for some key characteristics. This photo shows P. tremuloides (upper left), P. balsamifera (upper right), and P. grandidentata (bottom). The darker leaves are the upper side, and the lighter leaf shows the underside.

Trembling aspen (P. tremuloides) gets its name from its leaves that tremble, or shake, in the wind thanks to its flattened petioles. Big-toothed aspen (P. grandidentata) also shakes in the wind, but gets its common name from its leaves' large, coarsely toothed margin. Balsam poplar (P. balsamifera) is also known as Balm-of-Gilead but balsam poplar is also used interchangeably with cottonwood (P. deltoides) - the balm is made from the sticky buds.

	P. tremuloides	P. grandidentata	P. balsamifera
Petiole, in cross-section	Flattened	Flattened	Round
Distribution	Statewide	Statewide
Shade tolerance	Intolerant	Somewhat tolerant
Mature bark	Smooth top, ridged below	Smooth top, ridged below	Smooth top, ridged below
Alternate leaves	Round, short-pointed, finely toothed	Broadly egg-shaped, coarsely toothed	Ovate, fine round teeth, rusty blotches below
Buds	Dark brown, shiny, sticky	Dull gray, slightly hairy, not sticky	Resinous, sticky
Flowers	Catkins before leaves	Catkins before leaves	Catkins before leaves
Wood (see linked article for more info)	Close-grained, soft, little scent	Close-grained, soft, little scent	Coarser-grained, foul odor when green

Do you want to learn more about trees?

Maine Trees, Top to Bottom is for anyone interested in trees - beginners, back-yard naturalists, and more serious enthusiasts. The variety of student backgrounds leads to lively discussions and shared learning (I always learn something new) based on published literature, direct observations, and oral traditions. If you're interested in trees and want to know more about them, this class is for you!

The class has evolved over the years and will continue to develop in its format and its teaching tools. Building on the Forest Trees of Maine and Natural Landscapes of Maine, the six-week class is designed to equip students to identify the tree species that characterize Maine's forest communities. Learn to use dichotomous keys and understand botanical terms as you look at trees close up and from a distance.

Currently, Maine Trees, Top to Bottom is structured into six two-hour sessions. Each session introduces a couple of tree related topics and includes hands-on specimen identification (leaves, twigs, bark, fruit, flowers) as well as outdoor practice on trees surrounding the venue. As might be expected, topics range from roots-soil upward to trunk-nutrient transport to leaves-canopy. Though trees are the focus, we also bring in discussion of natural communities and the relationship between trees and the animals that live in those communities.

Interested? Watch for the spring calendar at Lewiston Auburn Senior College. You can also bring Maine Trees, Top to Bottom to a place near you as a six-week class or as a four-hour introductory session. For more information, contact treestoptobottom@gmail.com.

Flat-faced bark of Basswood

Basswood (Tilia americana) is more common in our area than I ever imagined when I began studying botany in general, and trees in particular.

A tree has many features that are useful in identification. The first feature most of us see is the bark, though that's often discounted because a) the leaves get most of the publicity and b) many of the barks look the same. Until I read BARK: A Field Guide to the Northeast, I mainly relied on the leaves, considered the twigs and buds, and only rarely took much note of the trunk standing literally right before my eyes.

One of the challenges in using bark as an ID tool is that most trees have a youthful, mid-age, and mature form. Even after reading BARK, I tended to group mature trees into one of three categories: smooth (like beech), peeling (like paper or silver birch), or ridged-furrowed (a huge group including oak, maple, elm, pine, hemlock and many, many more).

Basswood bark had, in my mind, gotten lost in the ridged-furrowed group. Yesterday, however, I learned a new character to its ridges that I expect will make this species easier to identify. The furrows are shallow, and the ridge face is flat. Also, the ridge-furrows run vertically up the trunk in long linear patterns. Basswood leaves are also pretty distinctive with their heart-shaped asymmetrical base and light-colored bracts that highlight the tiny flowers.

Trees are part of, and largely define, natural communities by giving the community vertical structure and also lending a name - White Pine Forest, Red Maple Swamp, or Pitch Pine Woodland for example. Basswood is characteristic of a Maple - Basswood - Ash Forest which you can read about here: http://www.maine.gov/dacf/mnap/features/communities/maplebassashforest.htm.
Learning more about the different features of each tree, as well as those with which it is often associated in a particular landscape, makes it easier to pick out of a crowded forest or woodland.

Shaggy Shagbark Hickory

Big-toothed Aspen

Big-toothed Aspen (Populus grandidentata) is fairly abundant around our house, lining the discontinued dead-end dirt road on which we live and showing up occasionally along the paved nearly-two-lane back roads. Fifty years or so ago, pastures and hay fields characterized farmland whereas only a few open farm fields remain today. Where the Big-toothed Aspen stand, you can see the fairly even ground in contrast with more dramatic hummocks and hollows pocked with boulders in less accessible areas of the forest.

In an early successional forest, pioneer species such as Big-toothed Aspen (P. grandidentata), Quaking Aspen (P. tremuloides), Gray Birch (Betula populifolia), and Paper Birch (B. papyrifera), establish where there is abundant sunlight after a landscape has been disturbed by fire, agriculture, or logging. Over time, other tree species take root and reach up into the canopy, out-competing the pioneers who are intolerant to shade.


Most of the Big-toothed Aspen's branching occurs high in the canopy where the leaves reach for solar energy used by chlorophyll to convert carbon dioxide (from the air) and dissolved minerals (from the roots) into sugars (photosynthesis). Oxygen is released in the process which makes plants, in general, a nice complement to us humans who exchange the oxygen for carbon dioxide.


The Big-toothed Aspen leaves flutter in the wind, a function of the flattened petioles (leaf stems). A side note, the fluttering gives this tree's Genus-mate Quaking Aspen (P. tremuloides) its common name as well as its species designation. Another side note, a third Populus species, Balsam Poplar (P. balsamifera) has a rounder petiole that does not catch the wind in such a shaking manner.  You might notice that aspen and poplar are used interchangeably for this genus.



Moving down the Big-toothed Aspen's trunk you might notice that the bark is very light-colored, like Paper Birch or Gray Birch. Closer inspection reveals a slight greenish tinge from chlorophyll that allows the bark to photosynthesize, a little bit anyway. On a Paper Birch, the white bark peels horizontally in thin strips that you'll never see on a Big-toothed Aspen or Gray Birch. Paper Birch and Gray Birch have lateral black lines, lenticels, that allow for gas exchange. The Big-toothed Aspen lenticels are more diamond-shaped, like little stars. The birches have a black chevron where the branches come out from the trunk - not as prominent on the Big-toothed Aspen.


If you follow the trunk down to the ground, you might be surprised to find the bark transitions to furrows and ridges! The ridges are quite distinctively chunky on older trees (see photo below with pencil for scale). On tall but less mature trees (like the photo on the right, below), the bark has been described as "zebra-like" with a light colored base laced with emerging, darker ridges.

And, of course, there's always the leaf. In spite of its tattered appearance, it's easy to confirm this aspen's identity and its names, both common and technical - Big-toothed Aspen, Populus grandidentata!

The White Oak Group

This fall, one of my quests is to collect leaves from all eight oak species that can be found in Maine forests. There are four in the black oak group: Northern Red Oak (Quercus rubra), Black Oak (Q. velutina), Scarlet Oak (Q. coccinea), and Bear Oak (Q. ilicifolia). Four more are grouped as white oak: White Oak (Q. alba), Chestnut Oak (Q. prinus), Bur Oak (Q. macrocarpa) and Swamp White Oak (Q. bicolor). Black oak leaves have bristly lobe tips, and the acorns take two years to mature while white oaks have rounded lobes or teeth with acorns maturing every year.

Thus far the teaching collection includes specimens from Northern Red Oak, Scarlet Oak, White Oak, and Swamp White Oak - halfway there!

The question today is what species of oak is represented by the leaves and bark pictured. Situated in a planted community, the tree is labeled White Oak (Q. alba). However, the Forest Trees of Maine describe White Oak leaves as dull above with rounded lobes, and the bark as having broad, flat, flaky ridges - neither of which seems to match up to this tree. Years ago I might have walked away thinking, "Okay, this is an atypical White Oak" but nowadays I question everything (especially myself). My goal isn't to discount someone else's work but rather to firm up my own understanding. So I'll bring you along on today's quest and questions - perhaps you'll weigh in with thoughts or answers.

First, what do I see? For me, direct observations in the field and photographs for later reference are the first step in identification. Instead of taking a field guide or key and trying to fit a specimen into that format, I attempt to learn by looking first at the features in front of me. Here's what I noted:

• Acorns: still forming, will continue to watch them develop. All eight oaks develop acorns: the black oak group takes two years to mature while the white oak group's acorns mature every year. This tree's acorns are still forming so I'll check back frequently over the next month or so for developments.
• Buds: still forming, will continue to watch. Winter buds begin developing at the leaf base during the summer. Breaking off the leaf doesn't reveal anything definitive yet so this is another feature I'll track over the next few weeks.
• Leaves: alternate, simple, lacking lobes, rounded "teeth" without bristly tips, deep glossy green above, wedge-shaped base. The rounded edges definitely put this leaf into the white oak group - no bristly tips. Not distinctly lobed like White Oak or Bur Oak, this can be narrowed down to either Chestnut Oak or Swamp White Oak - if we believe it to be a Maine tree. A planted grove may include other species so there's a possibility that it's a non-Maine native or a hybrid.
• Bark: deep fissures with orange at fissure base, irregular chunky ridges, gray-brown. 

Now let's compare observations and photo documentation with keys and field guides.

White Oak Quercus alba	Short-stalked (F) Cup bowl-shaped covering 1/3 or less of acorn (P)	2-4 times longer than acorn cup, hairless (F) End-buds red-brown, small, blunt, hairless (P)	Hairless (P)	Dull upper, rounded lobes (F) Evenly lobed, hairless, somewhat white below (P)	Broad flat ridges, flaky (F) Whitish, furrows broken into rectangular blocks (B) Whitish, slightly furrowed to scaly (P)
Chestnut Oak Q. prinus	3 times as long as cup, long & wrinkled (F) Cup bowl-shaped, tight scales free only at tip, < 1” across (P)	Sharp-pointed, broadly ovoid, hairless (F) End-buds narrow, sharp, > 3/16” (P)	Hairless (P)	Shiny upper, shallow rounded lobes (F) 7-16 pair of rounded teeth, leathery, slightly hairy below (P)	Deeply furrowed (F) Firm flat-topped ridges broken horizontally into irregular blocks with crisp square edges – corrugated & angular (B) Dark, deeply ridged (P)
Bur Oak Q. macrocarpa	2 times as long as cup, margin fringed with long hair-like scales, short-stalked (F) Bowl-shaped with fringe of elongate scales (P)	Broad ovoid, blunt or sharp-pointed, coated with soft hairs (F) End-buds blunt and hairy, > 3/16” (P)	Yellow-brown, hairless to hairy; branchlets may have corky wings (P)	Dark green & shiny upper, violin shaped (F) At least one pair indentations divide leaves into 2 or more portions, somewhat hairy & whitish below (P)	Deeply furrowed, flaky (F) Deeply furrowed, rough scaly ridges are not flaky, thick irregular blocks (B) Light gray, shallowly grooved (P)
Swamp White Oak Q. bicolor	3 times as long as cup, margins fringed with scales, long-stalked (F) Bowl-shaped cup with stalks longer than leaf-stalks (P)	Roundish, blunt-pointed, hairless (F) Brown end-buds small, blunt, hairless (P)	Hairless (P)	Dark green dull upper, slightly lobed (F) 4-6 pair of large rounded teeth, sometimes shallow lobes, wedge-shaped base, white-hairy beneath (P)	Deeply fissured, broad flat ridges, flaky, inner bark orange (F) Irregular furrows, narrow scaly ridges broken into horizontal blocks (B) Light gray, ridged or flaky (P)

F  = Maine Forest Service. 1908 (rev 2008). ForestTrees of Maine. Maine Department of Conservation.

B = Wojtech, Michael. 2011. Bark: A Field Guide to Trees of the Northeast. Hanover: University Press of New England.

P = Petrides, George A. 1958 (1972 2^nd ed). A Field Guide to Trees and Shrubs. Boston: Houghton Mifflin Company.

Buds and acorns on the planted species will yield information toward making a definitive identification. The shiny upper leaf with 8-9 pair of lobes suggests Chestnut Oak. Now off to southern Maine in search of field species to compare with those planted.



UPDATE: Here are leaves seen on a sapling at Mt. Agamenticus where the Maine Natural Areas Program's Natural Landscapes of Maine has documented Chestnut Oak as a natural community. Though the Mt. Agamenticus Wildlife Management Area does not allow specimen collection, I was able to get this photo to use as comparison with the planted specimen above - what do you think?

First thing first

The first thing to know about trees is, what is a tree? Sounds like a simple question but go ahead, if you haven't thought about this before - what makes a tree a tree? This is one of the very first questions asked at Maine Trees, Top to Bottom.

Trees live for many, many years - decades and sometimes centuries. From its seedling start to its sapling stage and then as a young tree, it keeps reaching for sunshine at its top, stretching its roots through the soil at its bottom, and adding growth rings to its trunk. Shrubs also live for many years, but the above-ground parts of herbaceous plants (grasses, ferns, wildflowers) die back at the end of each season.

A tree has a single stem, unlike shrubs which have multiple stems at their bases. There are a few considerations to make here. For example, in a post-harvest forest you might find several stump-sprout trees coming out of one base, like the photo to the right. This happens after the original tree is cut down and a few dormant buds emerge and send up new main stems (trunks). Another scenario is where Gray Birch (Betula populifolia) or poplar/aspen may propagate vegetatively, that is, underground so you get a small grove of the same species. In both cases, think about the tree species and whether you'd usually, or ever, see it growing as a single-trunk tree. It is not uncommon to see a single Gray Birch or a lone Trembling Aspen (Populus tremuloides). Shrubs ALWAYS have multiple stems no matter where or when you see them - think of staghorn sumac, lilacs, or highbush blueberry.

A tree has a woody stem, unlike fibrous herbaceous plants. A woody stem persists year after year, adding more growth to the tips of the branches and roots, and more growth to the girth of its trunk. An example of a fibrous non-woody plant is blackberry whose dried canes persist through the winter, but new growth comes up every spring.

Size is another consideration when distinguishing trees from other plants. Mature trees are generally taller than 15 feet and have a diameter of more than 3 inches. Of course, tree seedlings and saplings won't meet these criteria but they will have single woody stems, and it's likely there are mature representatives in the same area. So that's it - a tree has a single woody stem and at maturity is taller than 15 feet with a diameter greater than 3 inches.