you just know it? Or did you
figure it out?"
was the question presented to me several years ago when I took a plant
identification class from Clem Hamilton, then director of the Center for Urban
are many plants that we memorize as themselves. We may know Daphne odora 'Aureomarginata' because of the
white edges to the leaves and the standout fragrant, pink flowers in late
winter. We may know bigleaf maple
because there is one growing in the park where we walk.
other plants we need to figure out, and plant identification can be a good
detective game if you have the right tools. Those tools are knowing what to look for whether you are
examining a bare winter twig or a plant in full leaf.
use a key to identify plants. A
key is a series of questions or qualifications that leads from a broad
description to increasingly narrow descriptions of a plant. For the persistent woody
non-coniferous trees and shrubs, the first place to start is the leaf arrangement.
usually are arranged along a stem in either an alternate or opposite
fashion. This is the best place to
start your ID, because there are far fewer species with opposite than there are
with alternate leaf arrangements.
out now and look at any member of the rose family, including apples (Malus),
cherries and English laurel (both Prunus). You will see a leaf (or leaf bud, if there are no leaves
yet) first on one side of the stem, then a little further along on the other
side of the stem. Members of the
rose family have alternate leaf arrangement.
most commonly planted trees and shrubs with opposite leaf arrangement include
maples (Acer), dogwoods (Cornus), horse chestnuts (Aesculus), and members of
the honeysuckle family, Caprifoliacaeae.
That family contains such genera as elderberry (Sambucus), snowberry (Symphoricarpos), Viburnum, Weigela, and, of course,
rules are made to be broken.
Within one of the most common opposite-leaved species, dogwoods, are two
notable exceptions. One is the
pagoda tree, Cornus alternifolia, which has, as its name explains to us,
alternate leaves. The other is the
giant dogwood, C. controversa; its binomial reveals the
"controversial" nature of its leaf arrangement.
those of you who appreciate a mnemonic aid, these most common opposite-leaved
groups can be shortened to: MADCAP HORSE, which stands for
next most important feature to examine is whether the leaves are simple or
leaves are not divided and each leaf is attached to the branch in some
fashion. The stem of a leaf is
called the petiole. Beeches
(Fagus), hornbeams (Carpinus), and hawthorns (Crataegus) are examples of trees
that have simple leaves. Some
well-known shrubs with simple leaves include mock orange (Philadelphus),
Cotoneaster, and blueberries (Vaccinium).
leaves are divided up into leaflets.
There can be a few leaflets, such as with Akebia trifoliata (three
leaflets) and Akebia quinata (five leaflets) or there can be many leaflets,
such as with Mahonia x media 'Charity' (up to 21 leaflets) and the tree of
heaven, Ailanthus altissima (up to 30 leaflets!).
leaves can be twice or three-times divided themselves. In other words, a leaf divides
divides again (and perhaps again).
The devil's walking club, Aralia spinosa, has enormous leaves 60 inches
long that are two or three times divided; total leaflets can be more 160. Nandina
is another shrub with leaves
that are divided more than once.
tell if you are looking at a branch with simples leaves or a compound leaf with
many leaflets, examine where the leaf attaches to the stem. If it's a leaf attachment,
you will see
a leaf bud in the axil. If you are
looking at where a leaflet attaches, then you won't see a leaf bud.
leaves can be arranged in a variety of ways. The leaves of a Mahonia, look like a feather; they are
bi-pinnate. Horse chestnut leaves
are palmately compound.
have simple or compound leaves, too.
Coral bells (Heuchera) have simple leaves. Columbines (Aquilegia) have compound leaves. Meadow rue (Thalictrum)
leaves, too, and one species, Thalictrum aquilegiifolium, even tells us that
its leaves look like a columbine.
up is the shape of the leaf. There
are quite a few different shapes, but some of the most common are cordate,
heart-shaped as in the linden Tilia cordata; ovate and elliptical, which are
close in shape and often used together ("leaves are ovate to
elliptical"); and lanceolate, such as the willowleaf pear (Pyrus
margins are a big clue to identification.
The margin, or edge, of the leaf can be entire, which means smooth and
uninterrupted by divisions. The
leaves of Skimmia japonica and Magnolias are entire. Leaves can also be lobed as those of the flowering currant
(Ribes sanguineum), sweet gum (Liquidambar styraciflua), and Japanese maple
(Acer palmatum). Some cultivars of
Japanese maple, such as 'Linearilobum',
are so deeply lobed that they appear almost compound.
is a selection of other leaf margin descriptions and examples of each: notched,
Ginkgo biloba; serrate, Prunus serrulata or Zelkova serrata; undulate,
Elaeaganus pungens; dentate, like teeth, Osmanthus delavayi.
as if that isn't enough, using flowers to "key out" a plant is even
more involved. Let's save that for
are many books that contain keys and more descriptive information on plant identification.
Look for these books and more at local
bookshops, online or read them at the Elisabeth C. Miller Library at the Center
for Urban Horticulture.
Dirr, Michael, Manual of Woody Landscape Plants: Their
Identification, Ornamental Characteristics, Culture, Propagation and Uses,
Stipes Publishing, 1998, 1250 pages, $52.80
Gilkey, Helen Margaret, Handbook of Northwestern
Oregon State University Press, revised paperback edition June 2001, 494 pages,
Twigs: A Wintertime Key to Deciduous Trees and Shrubs of Northwestern Oregon
and Western Washington, revised paperback edition, August, 2001, 118 pages,