Tuesday, June 5, 2012

A sparkling coat of death: saltwater cordgrass

Word-association time! Answer this question with the first thing that comes into your head: What does one do with watermelon seeds?

If you're like me, or like millions of other Americans who grew up where melons could be had, you probably answered something like "spit them". When we eat watermelons1, we eat a big bite of delicious fruit and are left with the inedible seeds. Those, we spit out. (If you're a kid and it's a lazy summer afternoon, you have contests to see who can spit them the farthest.) We've taken in the part that nourishes us (yum, watermelon!) and gotten rid of the part we don't need (ptui, seeds).

Now what if the seeds were poison, and watermelon were the only thing we had to eat? We'd be like  saltwater cordgrass (Spartina alterniflora). Native to the east coast of the USA, this plant grows in coastal sand dunes, where the only water available to it is thick with salt. In a habitat like that, most grasses quickly shrivel, drinking deep of seawater and still dying of dehydration. Spartina, though, thrives.

Spartina leaves. See the clumps of salt?
How does it manage? Like a person eating a slice of watermelon and spitting out the seeds, Spartina takes in seawater and actually spits out the salt. Specialized glands on its leaves exert a force stronger than osmosis, drawing the salt out of the water it sups, and excrete it onto the leaf surface in crystalline form. Until the rain washes them away, these crystals sit on the leaves and sparkle, visible to the naked eye.

Image source: Field Studies Council. "Spartina." Retrieved 10 Aug 2012 from <http://www.theseashore.org.uk/theseashore/Saltmarsh%20section/species/Spartina.html>

1. The older cultivars, not the new "seedless" ones.

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