Shimeji mushroom. Lyophyllum. しめじ。
Also known as "beech mushroom" or "clamshell mushroom."
As is shown in the saying "Kaori wa matsutake, aji wa shimeji" ("For fragrance, matsutake mushrooms; for taste, shimeji"), these are mushrooms with a good taste.
There are two basic types of mushrooms that are called shimeji, the one very expensive as it is difficult to cultivate, the other commercially grown and therefore easily obtainable.
The first one is also called "hon-shimeji" (Lyophyllum shimeji) or "real shimeji." It is an autumn mushroom of excellent flavor - some say, better than matsutake which is more about fragrance.
[Shimeji. Photo Ad Blankestijn]
The other is "buna-shimeji" (Hypsizigus marmoreus), "beech mushroom." This one is widely cultivated since the early 1970s. It is a very good substitute for hon-shimeji (and often sold as such).
Shimeji are straw-colored and have a cap of about 1 cm. Shimeji have pleasant crunchy texture and somewhat nutty taste. They come in either white or brown. Raw shimeji tend to be bitter, so they should be used cooked.
Shimeji is rich in umami compounds and is used soups, tempura and sweet simmered dishes. It is also used in Japanese-style spaghetti.