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Submodule 5: Most Common Western Rangelands Weeds

Plant Classification

Plants are classified or grouped by life span, growth habit, or life form such as grass, sedge, forb, or shrub. Let’s first look at differences in growth habit:

• Annual plants are herbaceous (non-woody) plants that complete their entire life cycle (i.e., germination, vegetative growth, seed production and senescence) in one growing season. Some annuals are known to go from seed to a fully grown plant in only one month! They often have a small root system relative to their aboveground vegetative plant material (stems, leaves, and flowers).
• Biennial plants require about two years to complete their life cycle. They develop roots and aboveground vegetative growth during their first year of life. Sometime during their second year, they develop flowers, produce seeds, and then senesce. Usually stems remain short. Many biennials require a vernalization, or chilling period, which is provided during the winter months.
• Perennial plants live for more than two years due to some form of vegetative reproduction. These plants can be woody, such as trees and shrubs (that are always perennials), or herbaceous (i.e., grasses and forbs). Most perennials produce leaves and stems for more than two years and also flower yearly, although there are some, like century plants, that flower only once in a lifetime. In areas with cold winters, perennial plants die back and then regrow in the spring.

 

It is also important to know the basic characteristics that differentiate major types of plants:

 

Grasses are flowering plants in the family Poaceae, which contains over 6,000 species. Grasses supply most of the world’s food grains including corn, rice, oats, rye, sorghum, wheat, and barley. They can be either annuals or perennials, and generally have the following characteristics:

• Fibrous roots – many long, slender, branched roots that are all about the same diameter. Most of the roots are found in the top 12 inches of the soil.
• Hollow stem (or culm) – contains nodes, or joints.
• Leaves – have parallel venation distinct from most forbs (or herbaceous plants). The sheath of the leaf wraps around the stem and the blades protrude from the stem.
• Flowers or spikelets – often inconspicuous. Florets are arranged on an inflorescence, or group of flowers. This is the site of seed production.

Forbs are herbaceous (non-woody) plants. Many have showy flowers, which are one of their identifying characteristics. They can be annuals, biennials, or perennials, and they grow to a wide range of heights and widths. Below are some general characteristics:

• Roots – usually have a single long taproot with many smaller branching roots.
• Stems – usually have a solid stem with leaves attached throughout its length.
• Leaves – most have net-venation and are attached to the stem by a petiole (stem holding the leaf to the central stem).
• Flowers – often very showy, producing many seeds.

 

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