Learning basic characteristics of a few families will help you identify a significant percent of plants you find. For instance, learning about Asteraceae (Sunflowers) will help you identify about 20% of all plants you encounter, Fabaceae (Peas) 8%, Brassicaceae (Mustards) 7%. 

Remember also that you can learn family characteristics by learning genera and species.  Learning about characteristics of some of the larger and more common genera (Erigeron, Penstemon, Astragalus, Eriogonum) will lead you to learning more about families. Learning what species a plant is will lead you to see its similarities to another plant you find that same day and then you will notice in your field guide that they are in the same family.  Through genus and species recognition in the field you can learn family characteristics by seeing the actual plants that possess those characteristics, not by memorizing those characteristics and then seeing the species.

Another aid in identifying a species is to use the process of elimination. You might not know what family, genus, or species your mystery plant is, but you do know some families and species that it is not. You do know what time of year you found the plant. You do know what elevation you found it at. You do know its flower color. You do know some members of the family you suspect your mystery plant is in. All of this helps.

Using plant lists in combination with a key for your area is another great aid in identifying mystery species, i.e., if you use the Flora of North America to identify a plant you find in Arches National Park and the FNA lists 1000 species in the probable genus, your job of keying that plant will be much more complicated than it would be if you used a plant list from Arches that has only 20 species in the genus.

Click to read helpful hints and details about keying.

What is a species? What is it we are trying to identify?
Stanley Welsh, author of A Utah Flora, tells us of a
species definition given to him by Stephen Clark:
“A species is a period of stability within a chaotic continuum
that allows, for a moment, a portion of the gene pool to be
circumscribed by a definition”.

Why do scientific names change?
1) International code
2) Re-examination of existing genera
3) Genetic research

Here is a different view of name changes and classification by genetic makeup
as expressed by Stanley Welsh in his 5th edition of A Utah Flora:

"Morphology is the over-riding consideration on which taxonomic judgments are and must be based.
Taxonomic interpretations based on all other fields of endeavor including but not limited to amino acids, nuclear DNA,
chloroplast DNA, and the modern numerology, will not prove more reliable ultimately than morphology.
Such esoteric studies are not free from the biases of interpretation; bias is simply moved to a different level."

"Husband and wife, using DNA analysis, might illogically be considered as distinct species!
Movement in thought away from morphological features, which can be observed by use of standard techniques,
to minutia of chemistry and ultra-structure, which cannot be observed by use of standard optical procedures leads to
an endless pursuit. However, are the arrangements of the modernists more reliable than those based on morphology?
Humans and rutabagas are much alike from a DNA standpoint, but not much alike morphologically."

"Modern workers clog the system with endless generic name substitutions, a kind of continuing one-up-man-ship,
which serves to get their names in print, but does not add much if anything to the understanding of plant taxonomy."

How do we identify a plant, to give a plant a name?

We work our way through books that lead us in a series of steps that place the plant in a large group (family) then a subdivision of the family (genus) and then a subdivision of the genus (species).  
This step by step approach is called "keying a plant".

There are many kinds of keys, ranging from those that work only by flower color, 
to those that start with flower color and then subdivide by family or by plant characteristics, 
to those that work only by plant characteristics.

Whatever key(s) one uses, if one wants to be sure to identify the plant correctly,
the results should be confirmed with a key that includes all flora for that state or region. 

Botanical keys do not fully describe a plant;
they give only those details necessary to distinguish one plant from another.
Some floras, such as A Utah Flora and the Flora of North America, add complete descriptions and comments to the keys.

BELOW ARE KEYS TO THE MAJOR PLANT DIVISIONS IN FOUR DIFFERENT FLORAS

Wingate and Yeatts' Alpine Flower Finder
Simplified, yet very effective key for the interests of most people. Incomplete. Less common and similar species are often omitted.
Notice that all Rocky Mountain alpine areas are covered by the key.
(One way of evaluating the accuracy of a flora book is to check on the authors' credentials.)

Scientific names are based on Weber.

Komarek's scientific names are based on Weber's names.

          The following two keys to the major groupings, cover large geographic areas, but they cover all species in that area.

                                Welsh's A Utah Flora                                                                                                                        Weber's Colorado Flora, Western Slope
                                                                                                                                                        
1. Plants with small scalelike leaves, usually with a single vein
(microphylls); reproduction by means of spores; flowers or
woody cones lacking. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
– Plants with large leaves, usually with more than a single vein
(macrophylls), if scalelike, as occasionally, otherwise different
from above; reproduction by spores or seeds, the latter borne in
flowers or cones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2(1). Stems jointed, fluted, and hollow in the internodes; leaves not
green, reduced to a whorl of connate scales at the nodes; plants
neither grass- nor mosslike .. . . . . . . . . . . . . . . Equisetophyta
– Stems not jointed; leaves green and imbricated, not whorled or
forming a sheath at the nodes; plants either aquatic and grasslike
or terrestrial and mosslike. . . . . . . . . . . . . . . Lycopodiophyta
3(1). Plants fernlike and with broad leaves or free-floating aquatics
with small overlapping leaves; reproduction by spores; flowers
and woody cones lacking. . . . . . . . . . . . . . . . Polypodiophyta
– Plants neither fernlike nor free-floating aquatics (except in
Lemnaceae); reproduction by spores and seeds, these borne in
flowers or cones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4(3). Seeds not borne enclosed by ripening carpels, but naked and
situated on the surface of a scale, these borne crowded together
on an axis and forming a cone; flowers not developed; leaves
typically needle- or scalelike. . . . . . . . . . . . . . . . . . Pinophyta
– Seeds borne in ripening carpels; plants with flowers; leaves
mainly not needle- or scalelike (Magnoliophyta). . . . . . . . . . 5
5(4). Flower parts mainly 4- or 5-merous; leaves typically net veined;
stems increasing in diameter by means of a cambium between the
xylem and phloem; cotyledons typically 2 . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Magnoliopsida
– Flower parts typically 3-merous; leaves typically parallel veined;
stems usually lacking a cambium or, if present, producing entire
vascular bundles; cotyledon 1 . . . . . . . . . . . . . . . . Liliopsida