Sea Rocket
| During a recent hike at Rocky Point, after several days of windy weather, I noticed how sand had piled up over the backshore plants, particularly the sea rocket. That got me thinking about the harsh conditions this tenacious plant has to endure. Sea rocket, a member of the mustard family, is a pioneer species, able to colonize areas of bare coastal sand where very few plants can survive. The sandy substratum is a very unstable medium for plant growth, and the lack of humus means that it's not only unable to retain moisture but is also nutritionally poor. |
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Sea rocket puts down a long taproot that holds it in place. The root then branches into an extensive network that tends to stabilize the sand. This species has thick fleshy leaves to help it retain moisture. It has also adapted to tolerate salt spray and its low growing form makes it less of a target for abrasive, blowing sand. Sea rocket may be buried by sand; when that happens it responds with increased growth and seed production. |
| If you spot sea rocket on the beach, take a close look at the seedpods. They look like little two stage rockets with a dividing boundary line about ¾ of the way up from the bottom. I tugged on one to get a closer look and the bottom part of it popped off neatly at the boundary line. This is another of Mother Nature's inventive mechanisms to ensure survival of the species. Both sections of the pod contain seeds. The lower part has a corky composition so |
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There are two species of sea rocket found on the West Coast. American sea rocket (Cakile edentula) is thought to have been introduced from the East Coast, arriving more than 100 years ago. It is still found on the Atlantic coast and also around the Great Lakes. Another species, Cakile maritima is the more recent arrival. It originated in Europe and apparently arrived in California in the 1930s, where it has replaced most of the C. edentula. The European species has also been found in a few places along the west side of Vancouver Island.
While at Rocky Point, I decided to get some photographs of the sea rocket. Oddly, the shape of the leaves did not seem to match the descriptions of the American sea rocket that I expected to find. I could not however find any good references to tell if this might be European sea rocket. I sent pictures of the leaves and pods to Dr. Eugene Kozloff. He wrote to me that he prefers to use the fruit for identification. (According to the New York Public Library Science Desk Reference, the fruit is the entire seed-bearing organ of a plant, or in this case, the pod.)
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Dr. Kozloff says that in C. maritima, the blades of most leaves are deeply lobed in a pinnate pattern. On both broader sides of the fruit, the two segments are separated by a suture that is shaped like an |
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In C. edentula, the leaf blades usually have a wavy margin, or are just shallowly lobed near the base. The two segments of the fruit are separated by a simple constriction. The petals are about 6-8 mm long. |
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With this information, it appears that Whidbey Island has both species of sea rocket. At Rocky Point and the Dune area of Deception Pass State Park (both on northwest Whidbey Island), I found mostly European sea rocket (C. maritima) but also a few C. edentula. At Ala Spit and Monroe Landing (both on the east side of Whidbey Island), I found only American Sea Rocket (C. edentula).
Sea rocket is an annual and several nights of below freezing temperatures in late October have caused it to shrivel up and wilt away so further investigation will have to wait for spring.
Sea rocket is just one of many species of fascinating plants that live in the harsh environment of the backshore.
Mary Jo Adams
Beach Watcher,
Class of '99
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