Dichotomous Keys
•1a. small flowers at base of spadix usually surrounded by spathe(modified leaf)...Arum F.(Araceae)
•1b. flowers not as above...............................................................................................(2)
•
2a. flower parts in 3's, parallel leaf venation (monocots)...................................(3)
•
2b. flower parts in 2's, 4's, 5's (rarely 3's), netted venation (dicots).................(7)
•3a. ovary superior..........................................................................................................(4)
•3b. ovary inferior............................................................................................................(5)
•
4a. sepals & petals showy, stamens 6...................................................................Lily F.(Liliaceae)
•
4b. sepals green, petals showy, stamens 2-6.......................Spiderwort F. (Commelinaceae)
•5a. flowers radially symmetrical..................................................................................(6)
•5b. flowers bilaterally symmetrical...................................................................Orchid F.(Orchidaceae)
•
6a. stamens 6......................................................................................Daffodil F. (Amaryllidaceae)
•
6b. stamens 3..........................................................................................................Iris F.(Iridaceae)
How This Tool Can Help You Identify
Plants!
Marion Lobstein
mblobstein@earthlink.net
What Is a Dichotomous Key?
• A dichotomous (“forking”) key is:
– An artificial or “man-made” tool for
identification
– Structured with pairs or couplets(2) of
choices called “leads”
• Selecting the choice that best describes the
specimen to be identified, then leads you to
another set of choices or to the identification of
the specimen
How to Use a Dichotomous Key
• Start at the beginning of the appropriate key – family,
genus, or species key
– if you can recognize the family, you may look up that family
in your Flora and proceed to the genera key
– if you recognize a genus, you can go to the species key
• Read all choices in couplets/triplets
– it can be misleading to jump ahead without
considering choices
• Look up any terms you do not know in the glossary
of the Flora, in other references such as Harris and
Harris, or go to the web
How to use (cont.)
– Why look up terms you do not know?
• This can be tedious but necessary
• This is why we will cover terminology of structures such
as flowers, fruits, stems, leaves, etc., in lab
– Do not estimate sizes that you can
measure with your metric ruler
•
How to use (cont.)
• Keep notes on all steps taken in order to be able to
back track, if your identification is incorrect
• In making choices, remember this is a man-made
tool and using it sometimes is as much art as
science
• Practice with known species – weeds are great to
learn to use these keys!
• PRACTICE, PRACTICE, PRACTICE!!!
Key points from “Approaching the
Keys” pp. 87-92 in the Flora:
• Keys are artificial– keys may contain groups that are unrelated
but share common characteristic such as being aquatic
• Scan the layout of a key to see how couplets are organized
• Couplet – pairs of descriptors that will lead you to ID of your plant taxon
(level of classification such as family, genus, species) or to another couplet
– Lead (line) – each begins with a number
– Each set of couplets will be indented (stair-step arrangement-you may
have to look for another page to find the second member of a couplet
– Always read both choices of each couplet
• If characters in your plant are not present, there are ways of
“sleuthing characters” (pp. 87 and 92)
P. 92 – Sleuthing characters
Keys-Information (cont.)
• Keys are based heavily on vegetative characters that you
can observe more of the year
– Arrangement of leaves
– Herbaceous or woody; vines
– Aquatic habitat
• In first keys effort made to minimize technical term but
may encounter those in later keys (use of glossary in Flora)
• Efforts were made to key characters to those observable
with unaided eye or a 10X ocular (handlens) except in
special cases such as Isoetes (pp. 137-141)
An Introduction to Structures
(pp. 88-90)
• Leaf arrangement and disposition
– Arrangement-alternate, whorled, or opposite
• Try to observe mature leaves – young leaves may appear opposite
or whorled when first developing
– Disposition-basal (at base of plant) or cauline (on stem)
• Leaf longevity
– Evergreen
– Semi-evergreen (tardily deciduous)
– Deciduous
An Introduction to Structures (cont.)
(pp. 88-90)
• Growth form (may be challenge to discern)
– Woody (secondary growth, perennial)
•
•
•
•
Trees Shrubs
Subshrubs (small shrubs)
Woody vines
– Herbaceous [annual or biennial or perennial (often
underground storage roots or stems]
• Herbs-erect, sprawling, trailing
• Herbaceous vines – specialized adaptations for trailing
(twining, tendrils, etc.)
An Introduction to Structures (cont.)
(pp. 89-90)
• Leaf Morphology
– Type
– Lobes and teeth
– Leaf location
•
Confirming Your ID (p. 90)
– Use other floras (Flora of West Virginia is helpful) (Flora of North
America is online) and other identification books (Newcomb’s Guide to
Wildflowers)
– Use “more traditional” taxonomy and consult the index in Flora of
Virginia for current scientific name or if you have used the Flora of
Virginia, you can use the synonym(s) (alternative scientific names) to
find “more traditional” scientific names used in popular guides
– Use online resources such as USDA Plant Database or Digital Atlas of
the Virginia Flora
For additional information on distribution, can visit the Digital Atlas of the
Virginia Flora (www.vaplantatlas.org/) for distribution maps and color
photographs of many species
Learning Families
• Learning to recognize larger families facilitates process of
id to go directly to the family
– Distinctive characteristics
– “Gestalt” (feeling it looks like a composite)
• Some large families you may want to learn to recognize
are:
–
–
–
–
–
–
Apiaceae
Asteraceae
Brassicaceae
Cyperaceae
Euphorbiaceae
Fabaceae
--------
Juncaceae
Lamiaceae
Poaceae
Ranunculaceae
Rosaceae
Rubiaceae
Apocynaceae
– ADDED: former “Lily” family or Liliaceous plants or even former scrophs
and former saxifrage families with which you are familiar
Other Points in Approaching the Keys (p. 92)
• Winter identification
– No effort made to have keys for this aspect of plant life
cycle
– Some identification points are made for this group on p. 92
• Characteristics of major groups of plants
– See page 91
Introduction to Taxonomic Treatments
Treatments of 189 plant families represented in Virginia are presented alphabetically within five
major groups:
Lycophytes (Clubmosses, Spikemosses, Quillworts)(3 families)
Pteridophytes (Ferns and Fern Allies) (17 families)
Gymnosperms (Conifers) (3 families)
Angiosperm Dicots (Dicot Flowering Plants) (128 families)
Angiosperm Monocots (Monocot Flowering Plants) (38 families)
In addition to the family description, each family treatment (other than those families with one genus)
comprises a key to that family’s genera and description of each genus. Likewise, each genus
treatment (other than those with only one species in that genus) includes a key to the species and
infraspecific taxa of that genus and a description of each.
LYCOPHYTES
Major groups and keys to those groups
• Lycophytes and Pteridophytes – Key A
(primarily)
• Gymnosperms – Key B
• Dicots (herbaceous)–mixed in keys D (cacti), N
through S
• Monocots-M (primarily)