A Simple Botanical Key to Several Forage and Weedy Grass Seedlings For Use in a
Student Laboratory Exercise'
J. R. George and G. E. Pepper'
ABSTRACT
florescence. In addition t o classroom use, this key should
be helpful for anyone wishing to evaluate a new seeding
of forage grasses.
A dichotomous key using vegetative characteristics permits identification of grasses before emergence of inflorescences. Nine forage
species and seven weedy grasses commonly found in the northern
U. S. are described. Simplicity in design and terminology makes
this key useful either as a laboratory exercise in crop science classes
or by individuals wishing to evaluate a new forage seeding. Isolated
plants can also be identified, or established stands can be evaluated
before flowering. The use of potted specimens from the greenhouse and seedlings grown in the laboratory sandbench increases
the effectiveness of this botanical key as an instructional tool.
MATERIALS A N D METHODS
Nine forage grasses and seven weedy grass species were used in
this study (see Fig. 2 for scientific names). Approximately 50
seeds of each species were seeded in flats at a depth of 0.64 to 1.27
cm (Vi to !h inch). A thin layer of vermiculite was applied to the
surface of the soi1:sand:peat mixture (1: 1 : l ) to minimize surface
drying and crusting.
The flats were placed in the greenhouse, where they remained
throughout the 7-week period for study. Day temperatures ranged
from 23.8 to 29.4 C (75 t o 8 5 F) and night temperatures, from
12.8 to 18.3 C (55 to 65 F). Seedlings were grown under a 14hour photoperiod provided by gro-lux fluorescent lamps.
Binocular dissecting scopes were used to study the seedlings at
3, 5, and 7 weeks after planting. Several seedlings of each grass
species were studied in detail to insure the reliability of traits used
in the botanical key. The key was developed o n the basis of
vegetative characteristics and is designed so that the final distinguishing feature is always the ligule.
Colored slides for classroom instruction purposes were taken at
5 and 7 weeks after planting. Bellows, combined with a close-up
lens, were used to obtain intimate detail of the collar region.
Additional index words: Botanical key, Grass key, Grass identif ication, Grass morphology, Classification.
Miller and Manning (5) recently published a vegetative
botanical key to identify several small-seeded legumes. A
similar key seems appropriate for introduction of students
to both forage grasses and weedy grasses often encountered in new seedings in the northern U.S.
Hitchcock (4) is often used as a manual for grass identification and is very complete, since it contains all known
species that grow in the continental U. S., with the exception of Alaska. This manual, however, is too detailed
for introductory classes, and emphasis is placed on the
inflorescence in identification of individual species. Detail
on leaf morphology is not sufficient to permit reliable
identification of plants before flowering.
Phillips (6) prepared an excellent grass key based on
vegetative characteristics of the leaf. Approximately 800
vegetative descriptions of forage and weedy grasses are
presented. This key is appropriate for detailed study of
grasses but is too extensive for classroom purposes in a
single laboratory exercise. Burger (l),Carrier (2), and
Hartwig (3) have simplified keys, but each includes primarily forage species, with little or no reference t o weedy
grasses.
The purpose of this botanical key is to introduce students t o grass leaf morphology and to the use of a key in
identifying grass species. Identification is based primarily
on differences in morphology of the leaf collar region for
nine forage grasses and seven weedy grasses. I t is beyond
the scope of this key to include all grass species that might
occur in new seedings in the northern U. S., although
species most frequently found are included. N o attempt
has been made t o include species common t o the southern
regions of the U. S.
Advantages over other grass keys include simplicity,
inclusion of both forage grasses and weedy grasses, and a
means t o identify grasses before emergence of the in-
RESULTS
A N D DISCUSSION
Figure 1 illustrates leaf morphology characteristics used
t o identify the grass species. Although minor variations
in m o r p h o l o g y can b e expected for some of the species as
illustrated by Phillips ( 6 ) ,the drawings of the collar region
in Fig. 2 can be considered representative of the 16 grasses
contained in the botanical key (Table 1). This key is a
dichotomous type, offering two short descriptive choices
as described by Miller and Manning (5) for their legume
key. Use of the key consists of reading paired statements
(a couplet) identified by identical numbers, rejecting one
and accepting the other, and continuing t o the next couplet based on the number following the accepted statement. This procedure is continued until the accepted
'Contribution from the Department of Agronomy, Iowa State
University. Journal Paper No. 2, College of Agriculture, Iowa
State Universitv, Ames, Iowa 50010.
Associate Professor of Agronomy and Graduate Teaching Assistant, respectively, Department. of Agronomy, Iowa State University.
Fig. 1-Leaf morphology used t o identify grass species in the
botanical key.
18
George & Pepper: A Botanical
Key
19
Table1-Vegetative
keyto nineforagegrassseedlings
and
seven
weedy
grassseedlings.
I. Shoot ftattened, leaves ~olded in the bud ............... 2
2. Auricles clawlike, leaves folded in the bud ....... Perennial
ryegrass
2. Auricles
not
present
.....................
3
3. Bladebroad,tip taperpointed,
rhizornes
not present,
llgule
acuminate
................
Orchardgrass
3. Blade narrow,tip abrupt and boat shaped,rhlzomes present ...... 4
3
4. Leavesa paleblulshgreen,liguleroundedto acute. . Canadabluegrass
4. Leaves a dark green, ligule truncate ....... Kentuckybluegrass
I. Shoot cylindrical, leaves rolled in the bud .............. 5
5. Auricles
narrow
and clawlike
..................
6
6. Auricleshairy,bladeglossyand smoothbelow,rhlzomes
short,
ligule
truncate
..................
Tallrescue
6. Auricles
not hairy,bladeroughaboveand below,rhlzomes
long,
Itgtde truncate
to rounded .............
Quackgrass
5, Auricles not present or at Least not clawlike .............
7
7. Shenths
laterally
compressed
.................
8
12
Fig. 2-Leafmorphology
of the collar regionfor (1) Perennial
ryegrass(Loliumperenne),(2) Orchardgrass
(Dactylisglomerata),
(3) Canada
bluegrass
(Poacompressa),
(4) Kentucky
bluegrass
(Poapratensis),(5) Tall fescue(Festuca
arundinacea),
(6)
grass(Agropyron
repens),(7) Crabgrass
(Digitaria sanguinalis),
(8) Greenfoxtail (Setariaviridis), (9) Giantfoxtail (Setaria
faberii), (10) Yellowfoxtail (Seterialutescens),
(11) Sudangrass
(Sorghum
sudanense),
(12) Barnyardgrass
(Echinochloa
crusgalli), (13) Downy
bromegrass
(Bromus
tecto~um),(14)
bromegrass
(Bromus
inermis), (15) Reedcanarygrass
(Phalaris
arundinacea),
(16) Timothy(Phleum
pratense).(Ligule
A-Acuminate,
B-Acute,C-Rounded,
D-Truncate).
statement is followed by the name of the specimen in
question. For example, one would begin by considering
the two statements
preceded by the number 1. If the
shoot were judged to be cylindrical with leaves roiled in
the bud, one would continue on to the couplet preceded
by the number 5, thus ignoring couplets 2, 3 and 4. If
auricles were narrow and clawlike, one would continue to
couplet number 6, where either tall rescue (Festuca
arundinacea, a forage species, and quackgrass (Agropyron
repens), a weed species, would be identified as the specimen based on other auricle and leaf characteristics.
Since
each couplet is indented under the previous paired statements, begins with the same word, and is numbered consecutively,
no two couplets receive the same number.
Thus, the series of accepted statements leading to identification
of the specimen can be combined to provide a
morphological description of the grass species.
A hand lens or binocular dissecting scope is useful to
provide magnification of the leaf-collar
region for study
of plant specimens in the laboratory. This is especially
true for the 3-week stage, when seedlings are small. The
5-week stage was more desirable for class purposes, since
8, Collar and sheath hairy (either or both) ............ 9
9. Sheath long hairy, llgule roundedand membruneous.... Crabgrass
9. Sheathsmoothor shorthairy,llgulea fringe
of hairs
........
- ......
Greenor Glantfoxtall
8. Collar
and sheath
not hairy ...............
I0
I0.
Ligule
present
..................
IL
II. Baseof bladelonghairyabove,
ligulea frlnge
o[
halrs
..............
Yellow
fox-tall
If. Baseof bladenot longhairy,11gulerounded
and
membraneous
............
Sudaflgr
ass
10. Ligule
not present
.............
Barnyardgrass
7, Sheaths not Laterally corapresaed
..............
12
12, Collar and sheath hairy, sheath closed to near top ....... 13
13. Bladedensely
softhairy,rh[zon~es
notpresent,
llgule
long, toothed, rounded to acute ....... Downy brornegrass
13. Bladenot.densely
softhairy,rhl~omes
present,
llgule
short, entire, truncate to rounded ...... Smooth bromegrans
12,Collarand sheathnot harry,sheathsplitwithoverlapping
margins
. . 14
I4. Leafbladelightgreen,rhizornes
present,
ligulerounded,
long and not notched
..........
Reed canarygrass
14. Leafbladebluegreen,rhlzornes
not present,
ligulerotmded,
shorterand notchedon one or both sidesnear front....Timothy
leaf morphology is more easily observed without magnification because of the increased size of the seedlings.
Other traits,
such as the presence of auricles or distinguishing between compressed vs rounded sheaths, were
more obvious. The development of rhizomes and tillers
(Fig. 3) also was evident at the 5-week stage.
Figure 4 illustrates
the difference between folded or
rolled leaves in the bud. Some confusion may arise between grasses having a flattened stem [perennial ryegrass
(Loliurn perenne), orchardgrass (Dactylis glomerata),
Canada bluegrass (Poa cornpressa),
Kentucky bluegrass
(Poa pratensis)] and those having a compressed sheath,
unless the condition of leaves in the bud is observed. The
four grasses having a flattened stem all have folded leaves
in the bud. Those species having a compressed sheath
have leaves rolled in the bud. The condition of leaves in
the bud can be determined either through direct observation of emerging leaves or by means of a cross-section of
the upper part of the vegetative shoot.
The presence of narrow and clawlike auricles is emphasized in the key for quackgrass and tall fescue. Auricles were not always observed as prominent in the early
seedling stages, especially within 3 weeks after planting.
Even at 5 weeks, the auricles for tall fescue often consisted of a strong proliferation of collar tissue on the leaf
margin and either showed signs of being clawlike or at
least appeared as a prominent fold of tissue. However,
the presence of hairy auricles was always observed for tall
fescue but not for quackgrass. As the seedlings continued
to grow, the auricles became increasingly
clawlike for
both tall fescue and quackgrass.
20
Jour. of Agron. Educ., Vol. 1 , Oct. 1972
L E A V E S FOLDED
LEAVES ROLLED
Fig. 4-Use of t h e botanical key for identification of grass species
requires observation of leaves emerging from the bud.
Fig. 5-The ligule of green foxtail (left) consists of a fringe of hairs,
whereas t h e ligule of crabgrass (right) i s membraneous.
Fig. 3-Rhizomes were present for t h e sod-forming species and
tillers were developing for grasses having a bunch-type growth
habit at 5 weeks after planting. Illustrations are for smooth
bromegrass (top), tall fescue (center), and orchardgrass (bottom).
Although many keys distinguish between green (Setaria
uiridis) and giant foxtail (Setaria faberii) based on pubescence of the upper blade surface for giant foxtail, this
trait was not found consistently in our observations.
Thus, no attempt was made in this key to distinguish between seedlings of green or giant foxtail on a vegetative
basis. This is not considered serious, however, since competition to crops and control measures required for these
two weeds would be similar in the seedling stages.
The value of photographs for classroom instruction is
obvious in Fig. 5 and 6 . Figure 5 compares the ligules of
green foxtail (Setaria uiridis) and crabgrass (Digitaria
sanguinalis). The foxtails are easily identified by the
ligule, which consists of a fringe of hairs. The rounded,
membraneous ligule of crabgrass in Fig. 5 is distinctly different from the acuminate, membraneous ligule of
Fig. 6-Detail of the leaf collar region illustrates the acuminate
shape of a membraneous ligule for orchardgrass.
orchardgrass in Fig. 6. The use of colored slides further
enhances these various traits of the leaf-collar regions.
The advantage of living specimens over dried plant material for a student laboratory exercise is emphasized by
Miller and Manning ( 5 ) . We have found that photographs,
combined with potted, mature plants grown in the greenhouse and seedlings grown either in greenhouse flats or
the laboratory sandbench, make a very effective laboratory on vegetative identification of grass species.
Foth: Effective Teacher Evaluation
21