Weeds

Burdock

Dandelion

Weeds generally share similar adaptations that give them advantages and allow them to proliferate in disturbed environments whose soil or natural vegetative cover has been damaged. Different types of habitat and disturbances will result in colonization by different communities of weed species.

Naturally occurring disturbed environments include dunes and other windswept areas with shifting soils, alluvial flood plains, river banks and deltas, and areas that are often burned. Since human agricultural practices often mimic these natural environments where weedy species have evolved, weeds have adapted to grow and proliferate in human-disturbed areas such as agricultural fields, lawns, roadsides, and construction sites. 

Weed seeds are often collected and transported with crops after the harvesting of grains. Many weed species have moved out of their natural geographic locations and have spread around the world with humans.

Weeds may be unwanted for a number of reasons:

• competing with the desired plants for the resources that a plant typically needs, namely, direct sunlight, soil nutrients, water, and (to a lesser extent) space for growth;
• providing hosts and vectors for plant pathogens, giving them greater opportunity to infect and degrade the quality of the desired plants;
• providing food or shelter for animal pests such as seed-eating birds and Tephritid fruit flies that otherwise could hardly survive seasonal shortages;
• offering irritation to the skin or digestive tracts of people or animals, either physical irritation via thorns, prickles, or burs, or chemical irritation via natural poisons or irritants in the weed (for example, the poisons found in Nerium species);
• causing root damage to engineering works such as drains, road surfaces, and foundations

White clover

A number of weeds, such as the dandelion Taraxacum, are edible, and their leaves and roots may be used for food or herbal medicine. Burdock is common over much of the world, and is sometimes used to make soup and other medicine in East Asia. White clover is considered by some to be a weed in lawns, but in many other situations is a desirable source of fodder, honey and soil nitrogen.

A short list of some plants that often are considered to be weeds follows:

• Bermuda grass - perennial, spreading by runners, rhizomes and seeds.
• Bindweed
• Broadleaf plantain – perennial, spreads by seeds that persist in the soil for many years
• Burdock – biennial
• Common lambsquarters - annual
• Creeping Charlie – perennial, fast-spreading plants with long creeping stems
• Dandelion – perennial, wind-spread, fast-growing, and drought-tolerant
• Goldenrod – perennial
• Japanese Knotweed
• Kudzu – perennial
• Leafy spurge – perennial, with underground stems
• Milk thistle – annual or biennial
• Poison ivy – perennial
• Ragweed – annual
• Sorrel – annual
• St John's wort - perennial
• Sumac – woody perennial
• Tree of heaven - woody perennial
• Wild carrot – biennial
• Wood sorrel – perennial
• Yellow nutsedge - perennial