Thursday, February 10, 2011

The self drilling seeds of the filaree

Nature sure knows how to take care of itself.

I am familiar with the common stork's bill or heron's bill or filaree (Erodium spp.) and even killed one in my garden many years ago. They have pretty pink geranium- like flowers (yes they are related) with ferny green foliage.

But what makes them interesting is their seed dispersal mechanism.
The plant flings its seeds away and the seeds then bury themselves by drilling into the ground with the use of its long tail. So how does this work?

Filaree seeds with awn
 Scientists based at the University of California, Berkeley, and Harvard University have discovered that the inbuilt spring stores energy as the seed head dries and can flick the seed as far as 0.5 m. The tail, or awn (a hair- or bristle-like appendage) drills into the soil by twisting and untwisting in response to changes in humidity. According to the research "when humidity is low the awn dries, curls and drills the seed into the soil. When the humidity rises the awn uncurls, but backward facing hairs on the awn force the seed to move in one direction so that it continues drilling into the ground even when it uncurls."

If you would like to see a video of the 'drilling' mechanism visit this website at ScienceNow.

The downside to this particular plant is that the filaree has been very successful as an exotic invader. It was introduced into North America in the 18 century and is now an aggressive weed in the south western states such as California in the USA. They are found mostly in desert and grassland areas. The filaree foliage creeps along the ground covering the bare patches of soil ultimately smothering any native grass seeds.

Dried flower, spiral tail on seeds.

Addendum February 11:  Grasses  are the main plant family that have awns attached to their seeds. I could not find any other ornamental plants with awns.  Awns can be quite troublesome for pet owners of cats and dogs as the awn will attach itself to the skin causing lesions. In the worst case awns can travel into the animals body. Sorry don't mean to scare the pet owners out there.


  1. Dear Patty, The ingenuity of Nature never fails to amaze me [as indeed it seems that you find too]. I have been fascinated by your account of the Erodium and am mindful that this is but one of the myriad of the miracles of the natural world. I always learn something new from your postings and so enjoy reading them!

  2. Thank you Edith. I am a firm believer that Mother Earth will always be one up on us. We have a lot to learn from her.

  3. Mother Nature sure is clever in her inventions. I sometimes think that the only real difference between a weed and a garden flowers, is that the weed is so successful at propagating, that it becomes an undesired pest.

  4. Jennifer: somewhere I read that the difference between weeds and flowers is that weeds are very productive plants tho' short lived, while flowers live longer but are not so productive. It's an interesting perspective.

  5. The seeds have amazing form.Too bad it is invasive, because it really is a pretty innovative design.

  6. GWGT: Yes the seeds are quite sculptural, like tiny corkscrews.

  7. Amazing. I love the sculptural quality of the seeds but am a little disturbed by the fact that they can embed themselves into pets...ugh!

  8. Greetings from Southern California :-)

    I added myself to follow your blog. You are more than welcome to visit mine and become a follower if you want to.

    God Bless You, ~Ron