Wednesday, June 6, 2012

Glasswort by any other name: Salicornia

Yesterday we saw the most obvious way for a plant to deal with excess salt -- by taking it up and then immediately getting rid of it. That strategy works, as the dunegrasses' success can attest, but there's more than one way to peel an orange. Today, let's have a look at Salicornia, a genus with a lot of names (glasswort, pickleweed, sea pickle, marsh samphire, pousse-pierre...) and one interesting way of dealing with salt.
Salicornia virginica in flower.
The blossoms are those tiny
stringlike structures at the ends
of the branches.

Salicornia plants are odd-looking little things, though you might have to get close to see very much; most species don't get much larger than a foot tall. With their thick, succulent stems and tiny, scale-like leaves pulled in close, they look mostly leafless, and indeed the stems do most of their photosynthesis. Some species are edible, sold as a delicacy under the names "sea beans" or "samphire greens"; it's also been used in the glass industry, as a source of soda ash. These two uses, as a salty food and as a source of sodium carbonate, betray one important fact: mature Salicornia plants are chock full of salt. Yes, it's the same salt you're thinking -- sea salt, table salt, salt that sucks the water right out of living things.

How do they manage it without dying of dehydration? Glassworts, it turns out, have a special modification to their cells' vacuoles. Virtually every plant cell has a vacuole; it's essentially just a large membrane-bound bubble in the middle of the cell, which the cell uses to store water, control its size, and dump substances it doesn't want. For Salicornia, those substances include salt. It can keep salt locked up in the vacuole even when the concentrations inside are many times that of the rest of the cell, high enough that most plants couldn't keep the stuff contained and would die of dehydration. For these tough little oddballs, it isn't a problem; they just go on doing their thing with bubbles of saline death locked down right in the middle of every cell.

Hence their names: pickleweed for the salty flavor, sea pickle for the tolerance to ocean salinity, glasswort for being so rich in salt that the glass industry once used them as sodium collectors.

Image source: Folini, Franco. American Glasswort (Salicornia virginica) (6122382261). Retrieved 6 Oct 2014, from Wikimedia Commons: <>

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 <>

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

Monday, June 4, 2012

Salt Lovers' Week: meet the halophytes

Water, water everywhere, nor any drop to drink... Coleridge knew it, sailors have always known it, and anyone who's been to the beach certainly knows it: salt water is no drop to drink. Water with as much salt as is found in seawater can, in fact, be lethal. It literally dehydrates the drinker,1 making you thirstier even as you guzzle it down. Humans can't survive on salt water.

Neither can plants, and for much the same reasons. Salt water dehydrates them just as it dehydrates us, sucking the moisture out of their tissues and leaving them to wilt and die. There's a reason that ancient armies would salt an enemy's farmland if they wanted to destroy it utterly: salted ground can't support crops. Not even barnyard weeds will grow in land seeded with salt.

Like virtually everything in biology, though, this prohibition isn't absolute. Salty ground is harsh and unforgiving, but many species of plants -- halophytes -- have grown to live in it anyway. Dunegrasses take up the salt, then spit it right back out. Glasswort takes it up, puts it aside, and lives with it anyway. Tamarisks can tolerate salt well enough to take over the salt-crusted desert waterholes of the American West. Some plants can even live fully immersed in extremely salty water -- they must have managed it, if they were to survive the primordial oceans.

This week, look for a post each day, each dealing with one of these extraordinary plants as it thumbs its nose at the killing salts.

1. By osmosis. If you have two aqueous solutions (things-dissolved-in-water) side-by-side, the water will tend to move from the less-concentrated to the more-concentrated one. The liquid in your tissues has less stuff dissolved in it than seawater does, so the salt water literally sucks the water out of your body. Nasty.