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Saltmarsh Dodder

© Mary Jo Adams. WSU Beachwatcher's Beachlog Sept 2006.

A couple of years ago, after monitoring at Camano Island’s English Boom beach, John Custer and I decided to take a look at a small nearby area of salt marsh. As expected, there was a lot of pickleweed (Salicornia sp.) there but we were surprised to see what looked like tangles of delicate orange dental floss wrapped around it. I had no idea what the string-like material was but John suggested that it might be dodder and that proved to be correct; we were seeing saltmarsh dodder (Cuscuta salina).

There are about 150 known species of dodder. Its closest relatives are the morning glories and dodder used to be included in the morning glory family (Convolvulacea) but is now classified in a family of its own, Cuscutaceae. Dodders are parasitic plants and rely on their host plants for water and carbohydrate. Because they don't photosynthesize, they have no chlorophyll and their leaves are reduced to minute scales. Like the dodder we saw at English Boom, their color is often orange or yellow.

Dodder starts life as a seed that germinates into a seedling with a root anchoring it to the soil. The newly emerged filamentous stem immediately begins seeking a host plant. It has several days for this quest and if no host is found within that time, it depletes its energy store and dies. If luck holds and it finds a host, the dodder seedling wraps around it in a counterclockwise direction.

Small bumps on the dodder stem called haustoria tap into the host’s stem and the parasite/host bond is formed. With that connection, the dodder’s root becomes superfluous and disappears. The stem will twine upwardly around the host plant’s stem following that same counterclockwise direction until it reaches the top, and then will form small flowers that later give way to seed-bearing fruit. Dodders usually do not kill their host plants, but sap their growth and vigor.

While some dodders are host-specific, our salt marsh dodder can grow on several species other than pickleweed, including Jaumea carnosa, another Island County native with pretty yellow flowers and a nifty common name: salty Susan.

Speaking of common names, the dodders have some pretty imaginative handles as well: golden thread, witch's hair, devilguts, strangleweed, and tanglegut. As you may have deduced from the names, some dodders are not very popular. They grow on agricultural crops and ornamentals, making them first class pests. As such, they are classified as noxious weeds. There is also an invasive Japanese dodder (Cuscuta japonica) that has recently been found in several states, including California. With a growth rate of six inches per day, seeds that can remain dormant for many years, and the ability to grow on a wide variety of broad leafed plants ranging from small vegetation like alfalfa to large trees, this invader is judged to be a real threat.

Dodder is just one of many fascinating plants on Island County beaches and backshores. To learn about more of them, check out the recently expanded Shore Plants section of the EZ ID web pages.