tengusa; red algae (Gelidiaceae)
Refers to red algae of the family Gelidiaceae, especially Gelidium crinale. Commonly used to make agar (寒天).
Agar is made from tengusa seaweed.
Tengusa is known as a raw material for agar.
We gathered tengusa on the shore.
They boil down the tengusa to extract the base for agar.
Usually written in katakana; the kanji spelling 天草 is less common.
Kanji spelling; may be confused with the place name 天草 (Amakusa).
Hiragana spelling, also seen.
The origin of the name is uncertain. The kanji 天草 literally means 'heaven grass', but this is likely an ateji (phonetic) assignment.