Bureau of Land Management Learning Landscapes

What's Wrong With This Picture?

Invasive Weeds: A Growing Pain

Many weeds have pretty flowers but they are a growing pain. They crowd out native plants, harm animal habitats and increase erosion.

Seed Dispersal

Giving students a sense of how seeds are dispersed will help them learn to avoid spreading weed seeds when they are outside. Plant seeds are dispersed in a variety of ways. For example, among invasive weed seeds,

• The invasive leafy spurge seed pods build up pressure and explode, shooting seeds 15 feet away. They then bounce or roll.
• Small rodents and birds eat knapweed and Canada thistle seeds, helping to disperse them away from the parent plant.
• Dandelion seeds fly or float through the air. So do Canada and musk thistle.
• The invasive dyers woad and hoary cress seeds float on water.
• Houndstongue, burdock and cocklebur seeds hitch-hike on animal fur (and on human clothing).

Have students gather a variety of seeds. Examine the seeds with the students and discuss their natural dispersal methods. Have each student pick one seed he/she has found, and describe or demonstrate to the class its dispersal method(s). (The maple seed pod which is nicknamed the helicopter seed, and dandelion seeds are favorites for this activity.) Have students describe how humans influence seed dispersal, both intentionally and unintentionally. This might follow a discussion about what seeds are and how they can be collected (either outside, or at home in the kitchen, where most students can find apples, oranges, avocados, or other seed sources).

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Last Updated: June 2006