Black Radish - [Spanish Black Radish]
This Radish is particularly favored in Northeastern Europe, Poland, Lithuania, Russia and Hungary, so how it got called "Spanish" in the U.S. is beyond me. This is not a mild radish, falling somewhere in between the red radish and horseradish in pungency, so if you can't take the heat use the milder Daikon instead. Note that black radish is a lot drier than other radishes so substitutes may make recipes too watery. You will find Black Radish sold in markets serving Polish, Russian and Hungarian comunities.

Daikon Radish
Essential to Japanese, Korean and Chinese cuisines, these large white radishes are now available throughout the U.S. even in regular supermarkets. Asian markets may have several shapes and will also carry both roots and leaves in various dried, pickled and salted forms. Most markets remove the leaves because they yellow quickly but some farmer's markets will have them with leaves on.

These are fairly mild radishes, generally similar to a very mild red radish. Most Japanese diakons are shaped like fat carrots and are marketed in various sizes from a few ounces to several pounds, but in Japan spherical varieties are also grown. Korean daikons are fatter and shorter, often quite cylidrical. The photo specimens are: Korean, 4-3/4 inches diameter, 7 inches long and 3-1/4 pounds, about average size; Japanese, 2-1/4 inches diameter, 12 inches long and 1-1/2 pounds, again about average. Details and Cooking.

Red Radish - []
Here we have the standard American red radish (which is not always red) found in every supermarket and farmer's market in the country. An excellent addition to salads or just eaten whole, but the greens are usually in not very good shape and are a bit coarse anyway. For Slavic salads try to get Black Radish, or lacking that use Daikons, but for American recipes this is always the radish expected unless specifically stated otherwise. There is pretty much no difference in flavor or hotness with color or even shape (elongated versions are also sold.

Turnip - Asian
When you see East Asian recipes calling for "turnip". or bags of "salted turnip leaves" or "preserved turnip" what is really meant is one or another variety of Daikon Radish.

Turnip - Baby
These are usually special small varieties grown for the yuppie salad trade. The flesh is mild and may be of various colors: white, yellow, orange or red. They are generally sold whole with leaves on and need to be used quickly as they don't keep well.

Turnip - European - [B.Rapa rapa]
This turnip, grown all over the U.S. and Europe (except the British Isles), is available in any supermarket. Until the introduction of Potatoes from South America it was of critical importance in Northern Europe for the survival of both people and their livestock throught the winter. It grows well in colder climates, stores plenty of food value and can be kept in a root celar for some months after harvest. They can grow to over 2 pounds but for human consumption are usually harvested much smaller when they are more tender. The greens are also edible but commercial turnip greens are usually from a different variety with big leaves and small roots.