[Wood Ear, Cloud Ear, Tree Ear, Mouse ear, Jelly mushroom; Pepeiao (Hawaii); Jamur kuping, Tenga ng daga (Philippine); Ara-ge-ki-kurage (Japan); Mu-ehr (China); Bo'k-ni (Hokkien); Jamur kuping (Malaysia); Hakeke (Maori); Auricularia polytricha | also species A. auricula-judae (Jew ear), Hirneola auricula-judae and others (variation in color)]
This thin nearly black fungus is sold dried and will expand to about 4 times the dried volume and about 5 times the weight when soaked. It is often used in soups and stir fries in China and Korea for its slippery but crunchy texture. It has little flavor of its own but does absorb flavors from other ingredients it's cooked with. In the photo there are three dried ones on the left, each a little over and inch across, and on the right a rehydrated one that was originally the same size as one of the others. Some are blacker after soaking.
It is held in Chinese medicine to improve blood circulation and relieve atherosclerosis. Preliminary tests in Western medicine are encouraging and include confirmation of anticoagulant properties.
More on Mushrooms.
Fresh is now often available in the Asian markets here in Los Angeles. It is grown in China and package on foam trays and shrink wrapped in California. It is shiny on the concave side and matte on the convex side. The photo specimens to the left were purchased at a large Asian market in Los Angeles (San Gabriel) for 2019 US $6.11 / pound, labeled "Wood Ear".
This variety is now the one carried by the Korean Markets here in Los Angeles (2021). It is much larger than the regular ones and tan on the bottom side. Cooked it is black on both sides. Soaked, it is more leathery than the regular, and needs to be cut rather than torn apart. It remains a little leathery after cooking but has the crunch expected of Black Fungus.
Technically, "cloud ear" and "wood ear" are supposed to be different sizes / varieties, but that and any other distinctions are pretty much lost in commercial products. Most available in California is just called "Black Fungus".