Similar Climate of Origin
Lack of Natural Enemies
Fast, Early Growth
Plants cannot move, so they have developed strategies for dispersing their offspring away from the parent plant. Weeds are particularly good at this, and are often among the first to occupy disturbed sites. Seeds, and other plant propagules, can be dispersed by wind, water, animals, and humans.
Bull thistle, Canada thistle, and rush skeletonweed, like the common dandelion, have a fluffy umbrella-like structure that will carry seeds in the wind. Weeds like Russian thistle, halogeton, and diffuse and squarrose knapweed break off at ground level when dry and tumble with the wind, scattering mature seeds.
Weeds like perennial pepperweed, which often grows near water, can have seeds and roots that float, enabling long-distance transport in streams and rivers.
There are multitudes of ways animals can aide in weed dispersal. Seeds can pass through the digestive tracts of animals, be transported in mud attached to hooves and hide, and sprout from seed caches. Knapweeds seeds and seedheads cling to fur like burrs. The sharp thorns on yellow starthistle seedheads can jab into passing animal hide. Small barbs on cheatgrass and medusahead seeds facilitate being picked up by feathers and fur.
Humans play a big part in seeds dispersal today. Seeds stick into socks, shoes, and other clothing. Vehicles and farm machinery can get seeds and plant parts caught underneath. Transported soil, animal feed, and seed can contain weed propagules. We are particularly adept at weed dispersal because we travel both frequently and over long distances.
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