Similar Climate of Origin
  Lack of Natural Enemies
  Prolific Reproduction
  Seed Dispersal
  Fast, Early Growth
  Novel Weapons

Home>What Weeds Do>Weed Tactics>Seed Production

Prolific Reproductive Capacity

Commonly, invasive weeds produce large amounts of seed and/or exhibit rapid vegetative reproduction. These traits allow weeds to be aggressive invaders in many plant communities.

Pile of russian thistle tumbleweeds in a wash

Seed production
In nature, heavy seed production is a common reproductive strategy. Seeds are produced by the thousands in a “shotgun approach” to overcome obstacles like limited favorable sites and low seed and seedling survival. This approach has been perfected by many invasive weeds. Not only do many weeds produce thousands of seeds (a typical Russian thistle plant produces about 250,000 seeds), but both germination rates and seedling survival are high. In addition, weeds often form persistent seedbanks and can reproduce at a young age.

Cheatgrass seed head

Individual plants are also often good at adjusting to the local current conditions, a trait called phenotypic plasticity. Medusahead can produce one to six or more seed heads per plant, depending on conditions. One cheatgrass plant growing in ideal conditions can produce as many seeds as 10,000 cheatgrass plants growing under extremely crowded conditions.



Drawing of Canada thistle plants and rhizomes

Vegetative reproduction
Some plants don’t rely solely on seeds to reproduce. Through rhizomes or other vegetative structures, these plants can form thick, single-species stands. The grass in your own lawn is a good example. This vegetative reproduction occurs rapidly with invasive weeds. One Canada thistle plant can produce 364 feet of roots and 26 new stem shoots in 18 weeks. Perennial pepperweed stands can grow more than 50 stems per square yard. A single whitetop plant can send out 400 shoots in a year. Some other invaders with notorious vegetative spread are leafy spurge, Russian knapweed, and rush skeletonweed.

Images:
-Russian thistle pile: Mary Ellen (Mel) Harte (http://www.forestryimages.org, 9 October 2006).
-Cheatgrass seed head:Tom Heutte, USDA Forest Service, (http://www.forestryimages.org, 9 October 2006)
-Canadian thistle rhizomes: Public domain.

Text references:
-Archer, Amy J. 2001. Taeniatherum caput-medusae. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).
-Howard, Janet L. 1992. Salsola kali. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).
-Zouhar, Kris 2001. Cirsium arvense. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).
-Zouhar, Kris 2003. Bromus tectorum. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).
-Zouhar, Kris 2004. Lepidium latifolium In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: (http://www.fs.fed.us/database/feis/, 26 September 2006).