Tree Key

Non-visual Keys to Tree Identification
for the Species groups of Penquis Virtual Nature Center

Non-visual Keys to Tree Identification for the Species groups of Penquis Virtual Nature Center

This section will be expanded as time permits. Here we will concentrate on the tree and major shrub species found in central Maine. Elsewhere we will reach farther afield. For a current, comprehensive key to the trees, try this.

This key is designed to be used in conjunction with the Tree and shrub list and with the dicussion of The natural history of trees.

The key here is arranged in typical dichotomous fashion. That is, you are given a choice of two options that will take you in different directions. We will try to make it easy to get back to where you made the choice in case you find you made a mistake.

Most terms used should be self-explanatory. An exception may be the distinction between simple and compound leaves. Compound leaves are made up of leaflets which seem like the leaves of other trees. These leaflets grow from a central stem — which itself may be branched. The distinction is sometimes hard to make by feel. However, in summer and fall, you will be able to feel the buds that have developed for the next year’s growth. They are found at the base of the leaf stem, usually just beyond it on the twig. There are no buds at the base of the leaflets in compound leaves. Trace the stem back to where the central stem joins the twig, and you will find there the bud. Practice a bit. Once you learn to feel simple versus compound and opposite versus alternate in leaf arrangement you will be able to make many identifications, even in some complicated cases.

  1. Leaves linear, needle-like, or scale-like. Usually evergreen.Conifers
  2. Leaves otherwise or absentHardwood, broadleaf or deciduous species


  1. Needles in groups. Pines
  2. Needles otherwise.Spruce, fir, hemlock, cedar, larch

Spruce, fir, hemlock, cedar, larch

  1. Needles linear or needle-like Spruce, fir, hemlock, larch.
  2. Needles pressed to twigs and resembling scales of a fish Cedar

Spruce, fir, hemlock, larch

  1. Needles growing singly along branch in new growth, not flat, growing from woody pegs in old growth. Larches or tamarack
  2. Leaves or needles not as aboveSpruce, fir, hemlock

Spruce, fir, hemlock

  1. Needles single, relatively stiff, round or 4-sided in cross section.Spruces
  2. Needles single, linear, flat, not stiff. Fir and hemlock

Fir and hemlock

  1. Leaves flat, an inch or more long, not tapered from base to tip. Fir
  2. Leaves flat, usually less than an inch long, tapered from base to tip. Hemlock

Five per group (or bundle or fascicle in white pine). Two per group in red and jack pines.

Spruces 3 species here

Fir Fir (Abies) – Needles single, linear and flat, not stiff, long and narrow. Except for planted species, all firs in the northeast are balsam firs. They smell like Christmas trees because that is the most commonly used tree for that purpose.

Hemlock Hemlock (Tsuga) – Needles single, linear and flat, not stiff, shorter and wider than in fir.

Cedar Cedar (Thuja, Juniperus) – Leaves pressed flat to twigs. Northern white-cedar, also called arborvitae, is very commonly planted.

Larch or tamarack Larches (Larix)- Needles growing singly along branch in new growth and in groups from woody pegs in older growth. Loses leaves in winter.

Hardwood, broadleaved or deciduous trees

Leaves broad, either simple or compound, usually shed in winter in Maine. Leaves, buds, and twigs characteristically arranged in opposite or alternate pattern. In summer, check for leaf arrangement. In winter, check for bud arrangement. Opposite arrangement is found in maples, ashes, dogwoods, the honeysuckle family, which here means the viburnums primarily, and the buckeyes or horsechestnuts. Of these, maples, dogwoods, and viburnums have simple leaves (except in Boxelder, a maple). Ashes have compound leaves with leaflets arranged along a central stem in a manner reminiscent of the feather of a bird. The horsechestnuts have leaflets growing outward in a fan from the central stem like fingers from a hand.

  1. Leaves or buds growing opposite each other along twig. Maple, ash, dogwood, honeysuckles, horsechestnuts and allies
  2. Leaves or buds not opposite each other or clustered toward end of twig.Other hardwoods

Opposite arrangement

  1. Leaves simple (except in Box elder and elderberry), twigs slender. Maple, dogwood, honeysuckle
  2. Leaves compound, twigs heavy. Ash, horsechestnut

Maple, dogwood, honeysuckle

  1. Tree sized, leaves with toothed or irregular margins Maples
  2. Shrub or small tree, leaves with smooth or finely toothed margins. Honeysuckle and dogwood

Maples (Acer) Maple (Acer)- Red (Acer rubrum), sugar (Acer saccharum), silver (Acer saccharinum), striped (Acer spicatum) are the species of the northeast. Small to very large trees. Leaves simple, opposite, bark smooth in young, becoming broken into plates as tree ages. Fine twigs and buds.Norway is planted. It has bark in diamondy ridges. Fruits are double-winged and reminiscent of insects. They vary in size and separation angle between the wings. Norway maple fruits are found in summer and are widely spread. Red maple fruits are smaller, earlier, and with less spread. Sugar maple is the primary source of maple syrup and other maple products, though red maple also produces a usable sap that isn’t as concentrated and consequently requires more boiling.

Honeysuckle and dogwood families These are small trees or shrubs, generally growing in the understory. They are difficult to distinguish. Most of the dogwoods have smooth-margined leaves which does you little good in the winter. The honeysuckle family is widely varied ranging from small-tree sized elderberries which are greatly appreciated by wildlife — caution some are poisonous to humans — which have compound, papery leaves, to small shrubby hobblebush which has rounded, simple leaves.

Ash and horsechestnut Ashes (Fraxinus) have opposite compound leaves and heavy twigs and buds. We have white, green, and brown or black ash. Green ash is rare enough not to worry about. Bark is in vertical diamond pattern with that of black ash being quite flaky. If your feet aren’t wet, it isn’t a black ash. This species is often used to make baskets. Fruit is a shaped like winged oar about 1 or 2 inches long.

Horsechestnuts are a Eurasian tree that is often planted in farm yards. They have very heavy twigs and buds as large as the end of your finger. Their leaves are palmately compound, that is, the leaflets grow out from a central stem like the fingers from the palm of a person’s hand. The bark is flaky. Fruits are heavy nuts.

Alternate arrangement

Here it gets complicated. There are a lot of alternately arranged trees and shrubs. Too many, in fact, to be separated simply by non-visual cues. Nevertheless, we will present characteristics of some of the more important ones.


  1. Leaves retained in winter (if known). Rhododendrons, laurels
  2. Leaves shed in fall (if known) All other

Rhododendrons and laurels. This group is among the few broad-leaved evergreens in our area. All have narrow alternate leaves with untoothed margins. Rhododendron (Rhododendron) leaves are leathery and up to hand-length. Laurel leaves are smaller and less leathery (Kalmia). They are shrubs or occasionally small trees. Most are found primarily in moist areas, but mountain laurel is found in drier habitats.


  1. Leaves and buds clustered toward the end of the twig. Oaks
  2. Not as above All other

Oak (Quercus) – Alternate, deeply cut leaves and buds clustered toward ends of branches. Bark rough with mainly horizontal ridges and furrows. In our area, only red oak (Quercus rubra) is common. The fruit is the familiar acorn.

Aspen (Populus) – Quaking and bigtooth. Simple leaves, flat stems, alternate arrangement. Bark smooth but becoming rough near base in older trees. The leaf stems of these trees are flat and very mobile in the wind, leading to the quaking effect. With some practice you may be able to recognize that sound and thereby learn what tree you are standing under.

Willow (Salix) – Several species in our area. Scaly bark, soft wood, tough, slender twigs. Bark on large trees can be deeply ridged and furrowed. Leaves are simple (not compound) and are generally longer than they are wide with toothed margins. Willows are generally found on moist ground in bogs or along streams. Black willow, shining willow, crack willow (an escape from cultivation) white willow, Bebb willow, pussy willow are the only ones in our area that reach tree size, and the Bebb and pussy willow never get very big. The fuzzy catkins (flowering bodies) of pussy willow are well known. The willows can be difficult to tell apart, even for experts.

Birch (Betula) – Leaves alternate, simple. Bark smooth, usually shredding horizontally. Branches of yellow birch has peppermint smell when scratched. Bark at the base of older trees becomes ridged and platy. White birch is almost identical given non-visual cues, but the smell of the scratched twig is definitive. Gray birch has less shreddy bark and arrow-head shaped leaves. It is usually a small, poorly formed tree. Many planted European birches have similar characteristcs of leaf and bark and weaping habit. Birch sap can be used to make a syrup like maple, but is much thinner.

The rose family comprises a large group of small trees and shrubs. Blackberries, raspberries, and roses are shrubby and generally have spiny stems. Cherry (Prunus) – Finely toothed, alternate leaves. Bark breaks into squarish plates on older trees. Most of the cherries have little warty growths on the leaf stems, but they can be hard to detect without a lot of practice. Apples (Malus) and hawthornes (Crataegus) have short spur twigs or even spines in the latter group. Bark is flaky or scaly. Serviceberries (Amalanchier) are generally among the first plants to flower in spring, generally during mud season or just after. Leaves are small, roundish, and finely toothed. All these groups are favored food of wildlife. Even humans have been known to eat apples and cherries upon occasion.

Beech (Fagus grandifolia) – Alternate leaves with prominent ribs below. Smooth bark. Many beeches now showing rough, bumpy bark because of insect pests. Long, pointy buds. Beech is sometimes called the ‘idiot’s sign up sheet’ because of the habit some people have of carving their names into the bark. Test yourself: If John Q. Dim-wit carves his name into a beech at shoulder height, will the signature rise as the tree grows? Answer: No. Trees grow upward from a terminal leader and outward from a live layer beneath the bark. Johnny Dim-wit’s name will be at shoulder height as long as the tree lives, though some of the damage will heal into scars eventually.

Basswood, Linden (Tilia). Found widely in northern hemisphere. Leaves are alternate, toothed, hand-sized and unequally heart-shaped at the base. The fruit is distinctive with a leaf-like sail attached to a stemmed nut. Bark is smooth on young trees becoming thicker and furrowed into scaly ridges on older trunks in most species. Several North American species and some Old world species are planted as ornamentals.

image: Pixabay