Succulent plants come in a variety of shapes, sizes, and colors. They also hail from a variety of plant families. If there is one thing that unites these plants (other than their succulent habit) its that the vast majority of them around found growing in dry places. Whether its the heart of a desert or up in the canopy of a tree, succulence has evolved as a means of storing water. However, those of you living near salt marshes may recognize that a handful of salt marsh plants are succulent as well. How is it that plants so frequently found growing in standing water have evolved a succulent habit? The answer lies in salt.

Salt water is pretty bad for most plants. Just like we get dehydrated from drinking or eating high amount of salt, so too do plants. In general, salt both dehydrates plants and causes issues with nutrient uptake. Such is not the case for genera like Salicornia. Commonly referred to as glassworts, pickleweeds, or picklegrass, the various Salicornia are true salt-lovers.

Taxonomically speaking, the genus Salicornia has been called a “taxonomic nightmare.” Thanks to their highly reduced morphology and extreme phenotypic plasticity, delineating species among the genus is something best left to Salicornia experts. What we do know is that they all belong in the amaranth family, Amaranthaceae. All of this confusion should not take away from your enjoyment of Salicornia. Indeed, there is a lot worth appreciating in this family, including their ability to grow in conditions that would kill most other plants.

Salicornia are not simply salt tolerators that can hang on under saline conditions. They are true salt lovers or ‘halophytes.’ In fact, experiments have shown that various Salicornia grow much better when salt levels are high. This all has to do with the way in which these plants deal with their salty environment. Like all succulents, Salicornia have enlarged vacuoles that store water. However, these large vacuoles store more than good ol H2O. They also store salts and lots of them.

Photo by S.Ahmadihayeri licensed by CC BY-SA 3.0

The secret to Salicornia’s salty success has to do with osmosis. As you may remember from science class, substances in our universe like to move from areas of high concentration to areas of low concentration. In the case of water within the tissues of an organism, this often occurs between biological membranes. As you add salt to water, it actually displaces water molecules such that the more salt you add, the less concentrated the water becomes. That is why salt water dehydrates us. When you surround a cell with salt, water will diffuse out of the cell to balance out the concentrations on both sides of the cell membrane. Salicornia use this to their advantage.

These plants actively take up salt from their environment and dump it into their vacuoles. This means that the concentration of water within the vacuole is less than the concentration of water outside of the cell. Osmosis then takes over and water rushes into the plant’s cells. By concentrating salt in their vacuoles, Salicornia are always ensuring that they are on the receiving end of the water gradient. Water is always moving into these salty plants and not the other way around. By co-opting morphological adaptation to drought, Salicornia are able to conquer a niche that is largely unavailable to most other plant species. It also means that, despite all of the water in their environment, these plants maintain a pleasingly succulent habit.

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