The Biologist Is In: More Convergence on the Seaside

Tuesday, December 8, 2015

More Convergence on the Seaside

Cakile maritima on a southern California beach.
(I know this one is tasty, in real life.)

In a previous post (the-biologist-is-in.blogspot.com/2015/03/convergence-on-seaside.html), I discussed two seaside plant species that both have succulent, edible (and reportedly tasty) leaves.

Cakile maritima (Sea Rocket). [Brassicaceae, annual]
Crambe maritima (Sea Kale). [Brassicaceae, perennial]

Since then I've found a selection of other seaside plant species that all have succulent, edible leaves.

Blutaparon vermiculare (Silverhead, Saltweed). [Amaranthaceae, perennial]
Cakile edentula (Sea Rocket). [Brassicaceae, annual]
Cakile lanceolata (Sea Rocket). [Brassicaceae, annual]
Crithmum maritimum (Sea Fennel, Rock Samphire). [Apiaceae, perennial]
Eryngium maritimum (Sea Holly). [Apiaceae, perennial]
Limbarda/Inula crithmoides (Golden Samphire). [Compositae, perennial]
Salicornia bigelovii (Marsh Samphire, Dwarf Glasswort). [Amaranthaceae, perennial]
Salicornia europaea (Marsh Samphire, Glasswort). [Amaranthaceae, perennial]
Salicornia virginica (American Glasswort, Pickleweed). [Amaranthaceae, perennial]
Salsola soda (Barba di Frate, Agretti, Liscari Sativa). [Amaranthaceae, annual]
Sarcocornia quinqueflora (Beaded Samphire, Beaded Glasswort). [Amaranthaceae, perennial]
Sesuvium maritimum (Annual Sea Purslane). [Aizoaceae, annual]
Sesuvium portulacastrum (Sea Purslane). [Aizoaceae, perennial]
Tecticornia arbuscula (Shrubby Glasswort). [Amaranthaceae, perennial]
Tecticornia pergranulata (Blackseed Glasswort, Blackseed Samphire). [Amaranthaceae, perennial]

What is it about the seaside environment which is selecting plants to be succulent and edible? I've got some thoughts that I think lead to a partial answer. Let's break down the question into two parts.

Why are they succulent? The seaside substrates where these plants grow is typically composed of sand, gravel, or rock. These substrates don't hold water at all. Even though there is an ocean very nearby, any small plant growing above the high-tide line is effectively growing in the middle of a desert. Two main strategies for this situation are 1) grow extremely deep roots and 2) hold onto any water that they find. The first strategy is typified by Creosote (Larrea tridentata) and Mesquite (Prosopis spp.), neither of which would be described as edible. The second strategy of holding onto their water, means a plant will be succulent in some way or other. There are plenty of both toxic and edible succulent plants, so there is more to the story.

Why are they edible? Some of the plants are perennial, while others are annual. Before I started looking into it, I was thinking they were all weedy species. Weedy plants (or animals) are those that invest a lot of their energy in reproduction, while investing very little in self-defence of any specific individual (r-selected). For plants, this means they're typically annuals (or short-lived perennials) that don't invest much biological energy into growing spines, fibers, or poisons. In short, r-selected plants are more likely to be edible to generalist herbivores like ourselves. Now, that none of these species would count as a long-lived perennial (like a woody shrub or tree) may perhaps mean that the weediness argument has some value in understanding this group of plants.

Before I started looking up these species, I had never heard the name "Samphire" before. The name seems to be used generally for any succulent (and edible) weed growing on a rocky seaside of the northern British Isles. Several of them are described as being easy to grow in a garden setting. Some of the plants can grow directly in sea-water. These may be a bit trickier to grow in the home garden. I like growing interesting plants, so hopefully I'll be able to try growing some of them over the next several years.

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