Summarize the distinctive physical characteristics of grasses

Grass Diagram

The study of the physical features (external structure) of plants is
referred to as morphology. Morphology of grass plants is not just a
biological pursuit but can aid in many everyday decisions for the
forage manager. Grasses, whether annual or perennial, are mostly
herbaceous (not woody), monocotyledon plants with jointed stems and
sheathed leaves. They are usually upright, cylindrical, with
alternating leaves, anchored to the soil by roots. Grasses have leaves
(blades that narrow into a sheath), a stem (culm), a collar region
(where leaves attach to the stem), roots, tillers, and during the
reproductive stage an inflorescence or seedhead develops. Grasses may
have rhizomes or stolons and the collar regions have differing
variations of ligules, auricles, and blades (laminas). Inflorescences
of grasses also vary widely so during vegetative stages, the collar and
leaves help in proper identification and during reproductive stages the
inflorescence is very helpful.

Inflorescences are an arrangement of many spikelets composed of
individual florets. Grasses have three main inflorescence (seedhead)
types: panicle, spike, and raceme.

From a seed, primary (seminal) roots develop to nourish and anchor
the seedling. Eventually fibrous or adventitious roots develop from
lower stem nodes. Some grasses have underground stems called rhizomes
which grow horizontally before pushing above ground to a new shoot.
Some grasses have stolons which are above ground, trailing stems that
produce leaves, roots, and flowering shoots from the nodes. Some
grasses have both while some have neither.

Stems or culms are really a series of sections called internodes
which are separated by nodes. This is why grasses are referred to as
jointed or as "joints" (during the proliferation of marijuana). The
internodes or sections are very close together near the stem and but
lengthen or stretch out as the plant matures. The internodes are most
often hollow but a few grasses have internodes of white pith, such as
sorghum. The branching of leaves always occurs at the nodes and
develops from a bud that is between the leaf-sheath and the stem. When
branching results from nodes at the base of the plant it is called
tillering (suckering, stooling).

All grasses have a distinctive collar region. Proper identification
requires a look at this area where the leaf blade wraps around the
stem. If the leaf blade is pulled back, the collar region reveals a
unique combination of ligule, auricle, and meristemat tissue.
Barnyardgrass has no ligule or auricles. But other grasses will have a
ligule (hairy or membraneous growth at the blade-sheath junction).
Ligules vary in size, shape, and type. Many grasses will also have
distinctive auricles (appendages that wrap the blade around the stem).
The meristematic tissue will appear whitish and is the area of leaf
blade growth and expansion.

When learning about grasses, it is helpful to learn how certain
physical characteristics can affect other features. For example: meadow
foxtail can be described as a cool-season, pasture grass. But its
physical trait of having few leaves means it would not make a great hay
and even as pasture, protein content may be a concern. Corn is a common
warm-season grass but it is too tall for a pasture. How high a grass
can grow or other unpalatable features will enter into forage-livestock
decisions.

Whether a grass is an annual or perennial will determine many
forage-related decisions. Annual species usually have inflorescences on
more stems. Annual species typically require annual re-establishment
costs and labor. This also may lead to erosion hazards. Most annuals
grow during the spring and summer but some grasses are winter annuals
and when used carefully can add flexibility to a grazing system. Wheat,
annual ryegrass, and barley can extend the grazing seasons and reduce
winter feed costs. Perennials have inflorescences on some stems but
also produce vegetative tufts which will wait for two years or more to
produce an inflorescence. Perennials reduce the yearly cost and labor
or reseeding but must be managed to thrive or may not be as productive.

Each grass has its own list of environmental characteristics as
well. The following traits should be considered by forage managers:
winter hardiness, drought tolerance, salinity tolerance, soil pH
tolerance, production potential, and livestock suitability.


Horse

Different grasses have different palatability, digestibility, and
sometimes harmful effects on certain livestock. Livestock do have
preferences and will be choosy, so careful management is necessary to
ensure the best animal nutrition and pasture longevity and yield.

Understanding grass formation and structure can help managers wisely use the vast variety of grasses available.


© Oregon State University 2008
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