Today’s entry is the second in the series on the Coastal Flora of the Pacific Rim. This species, Cakile edentula, grew along all of the sandy beaches that I visited (a couple years ago) near Tofino, British Columbia. I was impressed by the ability of these plants to grow in the middle of large expanses of sand, in places where few other species could survive.
Cakile edentula, or American sea rocket, is one of the first plant species to colonize coastal dunes. It is extremely tolerant of salinity and salt spray. In order to grow in shifting sands, it first forms a large taproot that anchors it in place, then develops an extensive network of shallower roots. These shallow roots stabilize the dunes, eventually facilitating the succession of other plant species. Despite efforts to secure the sand, American sea rocket plants are frequently buried. Many of the plants that I observed were visible only by their growing tips peeking out of the sand. Fortunately for this species, such burial stimulates its growth.
I was surprised to learn that Cakile edentula belongs to the Brassicaceae, the same family as broccoli, kale, and so many other delicious vegetables. The thick, nearly succulent leaves did not remind me of brassicas at all. The flowers of the plants that I saw on Long beach had all senesced, but today’s other photo of a flowering Cakile edentula, taken by Daniel on Chesterman Beach, gave me the idea of examining the flowers more closely. When I found this macro of the species in flower , I was reminded of the little pink flowers and pods of radish plants (the brassica Raphanus sativus). The flowers of Cakile edentula can be blue to purple, pink to red, or just plain white. The flowers are perfect, radially symmetrical, and have four petals. These give way to silicles, seedpods that are less than twice as long as they are broad, and composed of two carpels separated by a seed-bearing partition. The function of these silicles is evident from their form. Once mature, the round upper segment will snap off and float away, carrying off its single seed to a (possibly) distant shore. The lower segment of the silicle also contains one seed (and sometimes none), but usually remains attached to the mother plant and will likely remain on the same beach. In this way, Cakile edentula ensures that new shores are colonized and that its original populations are maintained. This seems to be a good strategy, as American sea rocket is commonly found up and down the east and west coasts of North America. It has also been introduced in Japan and Australia, where it is invasive.
Interestingly, Cakile edentula has been shown to favour its kin over other members of its species that are not directly related to it. Susan Dudley and Amanda File (2007) found that Cakile edentula seedlings grown in a pot together formed fewer fine roots if they came from the same mother, suggesting that siblings did not compete with each other as much as unrelated plants. Although Dudley and File offer no explanation as to how plants can differentiate between kin and unrelated individuals, they did conclude that the mechanism occurred within the plant’s roots. If you’re in Canada, you can watch Dr. Dudley and her students investigate this phenomenon in “Smarty Plants: Uncovering the Secret World of Plant Behaviour“.
I loved this write-up, which revealed that the plant is MUCH more interesting than one would assume at first glance.
Thank you Daniel for all of your studies, hard work and excellent photography.
If I’m not mistaken I’ve eaten the seed pods and the leaves of this plant. Very mustard-like in flavor.
It would be worth the while for any seaside gardener to try growing the vegetable relatives of Cakile edentula in their veggie garden. I’ve had good luck with broccoli and other brassica vegetables in Virginia Beach,Virginia about a stone’s throw from the sea. There was some protection from heavy salt laden winds. Pampas grass, Tamarix, cacti and sand fence mainly.
The wild cabbage Brassica oleracea (from which broccoli, cabbage, kale, kohlrabi, Brussels sprouts and cauliflower were all derived by farmers) is only found growing wild on European seacliffs.
Other brassicaceae may not be so salt-tolerant. Sea kale (Crambe maritima) is a very salt-tolerant member of the Brassicaceae and grows close to the sea. It has large succulent leaves and edible starchy tubers. It is theorised that sea kale roots might have provided a lot of the carbohydrates for the pioneering humans in Britain after the last Ice Age. It was a popular vegetable as late as the 1800s and probably deserves more attention now.
Other popular crops derived from seaside plants include beets, asparagus and opium poppies. Samphire (Salicornia) is relatively unknown and still mostly local but has even more succulent flesh and is delightful.
Thanks to Tamara as well for writing this one!
Well, after reading that this plant is called American Sea Rocket, I was not surprised to hear it is a brassica. In parts of the US, the salad green arugula is called rocket, and it is definitely a mustard, which are brassicas. In terms of growing related plants in a seaside vegetable garden, per Scott’s comments, in California there are many commercial growers of things like brussel sprouts whose farms are right on the cliffs next to the ocean. We frequently go to Sunset State Beach, near Watsonville, California, and there is a large brussel sprout farm right next to the state beach. They seem to tolerate the salt very well, and like the sandy soil and cooler temperatures you get right next to the Pacific Ocean.
This species also occurs in the Chicago Region on beaches along Lake Michigan in Illinois, Indiana, and Michigan. See Plants of the Chicago Region by Swink and Wilhelm (4th Ed. p. 172).