Ah, you didn't tell us that although you are an Oregonian (by question), you are a Britisher (by recipe).

King Edward, Maris Piper, and Estima are British varieties, characterized as hardy, high-yield plants. The King Edward, as befits its name, has been called the "true British potato for centuries." It has pink and white skin and creamy flesh. Maris Piper and Estima, of apparently lesser lineage, have yellow/brown skin and creamy/yellow flesh.

In this country, where potatoes must survive without pomp and pageantry, we would call them good, all-purpose potatoes - perhaps boiling potatoes. Round red potatoes (such as La Rouge or Red Pontiac), long whites (such as White Rose) or round whites (Kathadin or Superior) will work in your soup. What you don't want is a high-starch potato, such as a russet.