Plant Science

Dessicated Dispersal

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Science  04 Oct 2013:
Vol. 342, Issue 6154, pp. 17
DOI: 10.1126/science.342.6154.17-b
CREDIT: P. MARMOTTANT ET AL., PROCEEDINGS OF THE ROYAL SOCIETY B 280 (11 SEPTEMBER 2013) © 2013 THE ROYAL SOCIETY

Equisetum plants (horsetail) have a lineage dating back to the Paleozoic, and these unusual vascular plants reproduce with spores. Marmottant et al. have now taken a closer look at how the spores get around. The spores have four long legs that, in humid conditions, are wrapped closely around the spore body, but as the relative humidity decreases, the legs straighten out. The change in shape is driven by the two-layer construction of the legs, with one layer having a greater tendency than the other to change volume in response to moisture, similar to the change in shape of old bimetallic thermostats in response to changes in temperature. The process is reversible, with legs furling and unfurling as the humidity goes up and down. In the naturally moist habitat that Equisetum frequents, a shaft of bright sunshine or a dry breeze can effectively change the local humidity surrounding a spore. As the legs move, so moves the spore. Occasionally the legs get stuck on each other, and, when they get unstuck, the release of elastic energy can propel the spore into a rather large leap. Whether crawling or leaping, repeated cycles of motility would increase the dispersion of these otherwise sedate plants.

Proc. R. Soc. B 280, 10.1098/rspb.2013.1465 (2013).

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