Plant Identification Basics

dichotomous key

a reference tool used for the identification of organisms where a series of choices between alternative characters progressively leads to the correct organism; “dichotomous” means “divided into two parts”, therefore dichotomous keys always give two choices in each step

morphological

having to do with the form and structure of a plant or animal

genus

taxonomic group of related species; first element of a scientific name, examples include Centaurea, Fallopia, Hieracium

species

a plant or animal with distinct features that can only reproduce with individuals of a similar nature; second element of a scientific name, for example in the name Centaurea stoebe, stoebe is the species

angiosperms

Flowering plants

Monocots

mono: one) have a single seed leaf, called the cotyledon, that emerges from the seed ex. grass

• leaf veins that form a parallel pattern

• floral parts (e.g. petals) in multiples of three

dicots

di: two) have two seed leaves or

cotyledons that emerge from the seed

ex. bean, pea

• leaf veins that form a net pattern.

• floral parts in multiples of four or five

herbicide selectivity

Some herbicides, such as plant

growth regulators like 2,4-D, target dicots or what are

often referred to as “broadleaf” plants. Other herbicides

target only grasses, an example of a monocot.

leaf arrangement

opposite, alternate, or whorled

• characterized

  by a single leaf per node

node

a joint or point of attachment for leaves and

branches

simple leaf

undivided, meaning it has

only one definite segment present between the stem

and the end of the blade

Compound leaves

• divided into definite and distinct segments called

leaflets.

• Compound leaves can be further grouped into

pinnately compound leaves and palmately compound

leaves.

• Pinnately compound leaves have leaflets

arranged on opposite sides of the leaf axis, similar to

a feather.

• The leaflets on a palmately

compound leaf radiate from a central point, like fingers

radiating from the palm of a hand.

Elliptic leaves

broadest in the middle

and narrower at either end.

Linear leaves

long and

narrow with the sides being close to parallel to each

other.

Lanceolate leaves

are much longer than wide,

with the widest point below the middle of the leaf.

Spatulate leaves

look kind of like a spatula, with the

tip being rounded and gradually tapering to the base.

Ovate leaves

are egg-shaped while oval leaves are round

to oval, lacking a pointed tip.

Cordate leaves

are heart-

shaped.

Entire margins

re smooth and do not have any teeth, notches, or

divisions.

dentate or serrate margins

toothed or saw-like

margin

Lobed leaves margin

indentations along the margin that cut inward toward

the leaf midvein.

Petiolate leaves

stalk (petiole)

that attaches them to the stem.

Sessile leaves

do not

have a petiole and are attached directly to the stem.

Clasping leaves

are sessile (i.e. do not have a petiole)

and have a base that wholly or partly wraps around

the stem.

sepals

outermost whorl of leaf-

like structures called sepals that protect the bud (Figure

9). Sepals are typically small and green, but may be

just as colorful as the petals. Collectively, sepals are

called the calyx. The next whorl of leaf-like structures

is the petals (Figure 10). They are usually colorful and

attractive. Collectively, petals are called the corolla.

stamen

the male reproductive organ

consisting of an anther, which bears pollen, and a

filament, the thread-like structure that supports the

anther (Figure 11). Field guides and keys often refer to

the number of stamens to help identify a plant. The

pistil is the female reproductive organ consisting of

the stigma, style, and ovary (Figure 11). The stigma

is the tip of the pistil and receives pollen. The style is

the narrowed portion that connects the stigma to the

ovary. Some flowers have multiple stigmas that field

guides and keys will refer to for identification. The

pedicel is the stalk that attaches the flower to the stem

(Figure 11). The pedicel is to a flower what the petiole

is to a leaf (see above, “What other leaf characteristics

florets

ray and disc (Figure 12). For example, oxeye daisy has

disc florets forming the center yellow portion of the

flower and ray florets forming the outer white “petal”

portion of the flower

inflorescence

Flowers more often than not occur in clusters that have

a specific arrangement called the

root systems

Plants with taproots have a single, dominant root that

penetrates downward to a considerable depth from

which lateral roots sprout. Fibrous roots are densely

branching roots that are similar in size with growth

oriented both outwards and downwards. Plants with

rhizomes have elongated, horizontal, below ground

stems that can emerge some distance from the mother

plant, giving rise to new plants. Stolons are similar to

rhizomes except that the elongated, horizontal stems

are above ground. Stolons root at the nodes or tips and

give rise to a new plant.