Prairie Grasses: The Grass Plant

 
      
 
 
 Vegetative parts | Other grasslike plants | Glossary
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It is strange that grass, the most common plant in most places in the world, is intimately known to rather few people. The structure of a grass is, however, just as easy to understand as that of any other plant. A typical grass is shown in Figure 1.

The roots of grasses, like those of other land plants, serve to anchor the plant in the soil and to conduct water and nutrients in solution from the soil to the plant parts. The main body of a grass comprises the culm, or stalk, and the leaves. In most grasses the culm is hollow and is composed of several tubes closed at the joints by solid tissue. The joints are nodes; the portions between them are internodes. One or more buds, which are undeveloped leaf or flower branches, may form at every node.

The leaves are arranged in two ranks, that is, alternately on opposite "sides" of the culm. The base of each leaf is at a node. The expanded upper part of the leaf is the blade; the lower part, which is usually split on the "side" opposite the blade, surrounds the culm, and is called the sheath.

At the junction of the sheath and blade, and facing the culm, there is almost always a small appendage termed the ligule. At the same place, but on the outer or lower "side", there is a band called the collar. Usually, on either side of the split in the sheath the collar bears projections termed auricles.

An important feature in the identification of grasses is the emerging leaf, that is, the new growth as it emerges from the sheath. The emerging leaf is described on page 13.

A description of the flowers is not needed here, because in this book grasses are identified by vegetative characters alone.

A fuller account of essential vegetative characters follows.

Vegetative Parts

Roots
In grasses there are mainly three types of roots (Figure 2). A fibrous root branches in all downward directions from the crown, as in crested wheat grass (Agropyron cristatum) or rough fescue (Festuca campestris). Rhizomatous roots, or rootstalks, are actually underground stems from which stalks and roots develop at intervals, as in western wheat grass (Agropyron smithii) , smooth brome (Bromus inermis), and some other grasses. Stolons are horizontal stalks that root at the nodes. The roots of creeping bent (Agrostis stolonifera var. major) are stoloniferous.

Sheath
The sheath may be round or compressed. Occasionally it is keeled at the midrib. It is usually of a paler shade of green than the blade, and is often tinged with pink or purple at its base. These tints are not consistent enough to be of much value in identification, except in a few grasses such as meadow foxtail (Alopecurus pratensis). A sheath may be split completely, split with one margin overlapping the other, or without a split (Figure 5). A ruptured sheath must be distinguished from one that is naturally split.

Ligule
The ligule may be a membrane or a fringe of hairs. In some species the ligule is not present. In texture and color it varies from thin and white, as in Canby blue grass (Poa canbyi), to thick and opaque, as in fringed brome (Bromus ciliatus). The length of a ligule may vary within a species, but its shape and color and the character of its margins are usually quite constant. The outer surface of the ligule is usually smooth, but it may be pubescent, as in reed canary grass (Phalaris arundinacea) and some species of Agrostis. The types, shapes, and margins of ligules are shown in Figure 6. Large ligules and those in old or dry material may be so frayed and broken that they are useless for identification purposes.


Figure 7. Types of collars

Collar
The band that forms the collar (Figure 7) may be vertically broad or narrow, continuous, or divided by a midrib. If it extends diagonally it is called oblique. The collar is usually smooth, but it may be hairy (pubescent) over the whole surface, as in quack grass (Agropyron repens), or it may have minute hairs (cilia) on the inner and lowermost portion of the margin. It is usually pale green or yellowish green, but it may be temporarily tinged with red, as in yellow foxtail (Setaria glauca).


Figure 8. Shapes of auricles and (right) a collar without auricles.

Auricles
Auricles (Figure 8) are appendages extending from the collar. They may be horizontally clawed, fully or slightly rounded, or rudimentary. Sometimes they are not present. When old or dry specimens are being examined care must be taken to avoid breaking off the auricles.

Emerging leaf
A developing leaf is closely surrounded by the sheath of the previously developed leaf (Figure 9). In the developing state, a blade may be conduplicate, that is, folded at the midvein with the margins meeting, or it may be rolled lengthwise with either one margin overlapping the other (convolute) or both margins turned inward toward the midrib (involute). Conduplicate leaves usually form a laterally compressed shoot, rolled leaves usually a cylindrical one. There are exceptions. In yellow foxtail (Setaria glauca) and barnyard grass (Echinochloa crusgalli) the leaves are rolled in flattened shoots, whereas in poverty oat grass (Danthonia spicata), June grass (Koeleria gracilis), and certain fescues, the folded leaves are in round shoots. In plains reed grass (Calamagrostis mortanensis) and Nuttall's alkali grass (Puccinellia nuttalliana) the leaves are involute in somewhat rounded shoots.

The shape of the emerging leaves can best be seen when the stalk is cut just below the ligule and examined with a hand lens.


Figure 1. A grass plant, showing the vegetative parts.

Blade
The blade (Figure 3) is usually long and narrow. Though ordinarily rather flat, it may be V-shaped, folded, or rounded. When it is so tightly folded that it seems to be solid and cylindrical, it is termed bristle-like. A rounded leaf may be U-shaped, cylindrical with one margin overlapping the other (convolute), or cylindrical with margins turned inward toward the midrib (involute). A blade may be constricted at the base, or sometimes twisted.


Figure 2. Types of grass roots.

Its tip may be sharp-pointed or boat-shaped, and the general shape may be tapered or mostly with parallel sides (Figure 4). The surface may be smooth, rough, or hairy, and the margins smooth, without hairs (glabrous), or with a fringe of hairs (ciliate). Veins may be so prominent on the upper surface that they form ridges. On the lower surface the midvein or midrib may be prominent enough to form a keel.



Figure 3. Shapes of blades, in cross section.



Figure 4. Shapes of blades and tips.



Figure 5. Split and unsplit sheaths, viewed directly and in cross section.




Figure 6. Ligules, showing (upper row) types (and, right a leaf without a ligule), (middle row) shapes, and (lower row) margins.



Figure 9. Shapes of emerging leaves, with, at right of each leaf, a cross-section view at the juncture of leaf blade and sheath.


Other Grasslike Plants

Some common plants, mainly the sedges and rushes, are in certain ways similar to grasses. Table 1 presents comparative information.

Table 1. A comparison of plant parts in the grasses, sedges, and rushes
Character
Gramineae
(grasses)
Cyperaceae
(sedges)
Juncaceae
(rushes)
CulmUsually hollow; cylindircal or flattened
Nodes conspicuous
Filled with pith, rarely hollow, usually three-sided
Nodes indistinct
Filled with spongelike pith, cylindrycal
Nodes indistinct
Leaf arrangementTwo-rankedThree-rankedThree-ranked
Leaf bladeUsually flat; often folded, involute, or bristle-like; glabrous or pubescentFlat, folded, or bristle-like; rarely pubescentChanneled or round, usually glabrous
Leaf marginsSmooth, scaborous, ciliateUsually scabrousSmooth
Leaf sheathUsually split,
occasionally closed
Usually closedOpen or closed
LiguleUsually absentAbsent of weakly developedAbsent of weakly developed
CollarDistinctIndistinctIndistinct
AuriclesPresent or absentabsentabesent
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Glossary

Definitions are limited to the sense of the word as it applies to vegetative parts of grasses in this publication.

acuminateof a blade, ligule, stolon, or rhizome: gradually tapering to a sharp point
acuteof a blade or ligule: abruptly sharp-pointed
annualof a plant: (noun) a plant that completes its life cycle in one growing season
(adjective) completing the life cycle in one growing season
ascendingof a plant part: sloping upward
auriclean appendage of a collar
bladethe portion of the leaf above the sheath
bulbousof a stalk: having a bulb-like base
chartaceousof a ligule: having the texture of writing paper
ciliateof a blade, collar, or ligule: fringed with fine hairs
ciliolateof a ligule or blade margin: fringed with minute hairs
claspingof an auricle: having the appendage extending directly into the collar and partly or completely surrounding the blade
collarthe band on the outer or lower "side" of the leaf at the junction of the sheath and the blade
compressedof a sheath: flattened laterally
conduplicateof a leaf: folded together lengthwise in the emerging leaf
constrictedof a collar: narrowed at the midpoint
continuousof a collar: extending from one margin of the sheath to the other
convoluteof a leaf: rolled lengthwise in the emerging leaf, with one margin overlapping the other
coriaceousof a leaf: leathery in texture
corrugatedof a ligule: having alternating ridges and grooves
crownof a plant: the region from which both stalks and roots grow
decumbentof a stalk: curved upward from a horizontal or slightly inclined base
dividedof a collar: separated at the midrib
emarginateof a ligule: notched at the tip
entireof a blade or ligule: having the margins continuous and not in any way divided
fascicleof leaves: a compact cluster
fibrilloseof a root: having fine fibers
filiformof a blade: very slender; threadlike
flaccidof a blade: lax and weak; lacking rigidity
flexuousof a blade: having alternate opposite curvatures
glabrousof a blade, collar, or sheath: without hairs
glaucousof a blade: covered with a waxy layer, which gives the plant part a bluish green color
hirsuteof a blade or sheath: having coarse, straight, rather stiff hairs
hispidof a blade or sheath: having stiff hairs or bristles
hyalineof a sheath margin: thin and translucent or transparent
hybridof a plant: a cross between two species of plants
involuteof a blade or an emerging leaf: having margins rolled over the upper surface toward the midrib
keel a ridge on the back of a sheath or blade usually along the midrib
lacerateof a ligule: having margins deeply and irregularly cut
ligulea thin appendage projecting from the inner surface of a leaf at the junction of the sheath and blade
linearof a blade: long and narrow with parallel sides
membranousof a ligule: thin, rather soft, and more or less translucent and pliable
midribof a blade: the central vein
muriformof cells: arranged like rows of bricks
obliqueof a collar: slanting and of varying width
obtuseof a ligule: blunt or rounded at the tip
papilloseof a blade or sheath: having minute nipple-shaped projections
perennialof a plant: (noun) a plant that lives for more than two years. (adjective) living more than two years.
piloseof a plant part: having soft, fairly long, straight hairs
procumbentof a stalk: partly prostrate
prostrateof a stalk: trailing along the ground
puberulentof a sheath: having fine minute hairs
pubescentof a plant part: having soft fine hairs
retrorseof hairs: bent downward or backward
rhizomean underground stalk from which, at intervals, shoots arise above and roots descend below; also called rootstalk
ridgedof a blade: having raised veins
rootstalka rhizome
rudimentaryof a plant part: imperfectly developed
scaberulousof a blade: having minute protuberances that are rough to the touch
scabrousof a blade: having small protuberances that are rough to the touch
scabrousof a sheath or blade: having rather thin, translucent, not green, dry margins
serrateof a ligule or blade margin: having sharp teeth
serrulateof a ligule: having fine teeth
sheaththe lower part of the leaf that surrounds the stem or shoot
stolonan aboveground creeping stem that roots at the nodes
stoloniferousof a plant: bearing stolons
stoma(plural: stomata) a minute opening in the surface of a leaf
striateof a sheath: having very narrow longitudinal lines of darker or lighter color than the adjacent tissue
truncateof a ligule: having the tip seemingly cut off at a right angle to the micrib
tuftedof plants: having shoots in a loose, compact, or dense cluster arising from a crown
undulateof a Mule: having a wavy summit
vein of a blade or sheath: one of the parallel structures that serve to support the leaf
villoseof a plant part: having long, soft hairs
 
 
 
 

Other Documents in the Series

 
  Prairie Grasses: Identified and Described by Vegetative Characteristics
Prairie Grasses: The Grass Plant - Current Document
Prairie Grasses: How to Identify a Grass
Prairie Grasses: Index of Latin Names
Prairie Grasses: Index of Common Names
 
 
 
  For more information about the content of this document, contact Grant Lastiwka.
This document is maintained by Linda Hunt.
This information published to the web on March 19, 2004.
Last Reviewed/Revised on March 5, 2015.
 

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