This is the dried tree fungus that looks like little shreds of black paper in Chinese Hot and Sour Soup. Black fungus (Auricularia polytricha) is an edible wild mushroom sometimes known as tree ear or cloud ear fungus, given its dark, ear-like shape. While predominantly found in China, it also thrives in tropical climates like the Pacific Islands, Nigeria, Hawaii, and India. Known for its jelly-like consistency and distinct chewiness, black fungus is a popular culinary ingredient across a range of Asian dishes. It has likewise been used in traditional Chinese medicine for hundreds of years. It is an important blood thinner.

Emerging research indicates that black fungus offers many benefits, such as protecting your liver, lowering cholesterol, and boosting gut health. It's also packed with fiber and antioxidants. (healthline.com)

From the manufacturer: 

For the fungus from Changbai Mountain, if you need to eat it quickly, soak it in warm water to make it swell. If you do not need to eat it quickly, soak it in cold water for 12 hours, which will have a better taste and richer nutrition. Storage method: cool and dry place

It is known as Mandarin Chinese: 云耳; pinyin: yún'ěr, lit. "cloud ear"[citation needed], Chinese: 毛木耳; pinyin: máomù'ěr, lit. "hairy wood ear"), and in Japanese it is called ara-ge-ki-kurage (アラゲキクラゲ, lit. "rough-hair-tree-jellyfish"). It is also known as black fungus, black Chinese fungus (or mushroom), wood ear fungus, wood fungus, ear fungus, or tree ear fungus, an allusion to its rubbery ear-shaped growth. 

While predominantly found in China, it also thrives in tropical climates like the Pacific Islands, Nigeria, Hawaii, and India. 

Known for its jelly-like consistency and distinct chewiness, black fungus is a popular culinary ingredient across a range of Asian dishes. It has likewise been used in traditional Chinese medicine for hundreds of years.