oxalic acid
A dicarboxylic acid found in many plants; used in chemistry and as a cleaning agent.
Oxalic acid is abundant in spinach.
Oxalic acid can bind with calcium to form stones.
Standard chemical term; katakana for シュウ is common in scientific contexts.
Rare kanji form using 蓚; not commonly used in modern writing.
From シュウ (蓚, a type of sorrel) + 酸 (acid). The kanji 蓚 refers to plants of the genus Rumex, which contain oxalic acid.