If you are wondering what those are, then you know how I felt when I first encountered them. After doing some research, to my great surprise, I found they are native to a huge stretch of land starting in Ireland and heading all the way to Japan, then veering south through China, Vietnam and hopping to Australia, at some point passing my original home, the UK. I first saw them in Hunan, China.
They are the tubers of Sagittaria sagittifolia, apparently known in English as 'arrowheads', on account of their shape. In Chinese, they are 慈菇 (Mand: cí gū; Cant: ci4 gu1). They are referred to in some older books as Chinese potatoes.
This aquatic root vegetable has little taste but is valued in Chinese cuisine for its texture ( and some supposed , fanciful, magical health benefits). Unlike most root vegetables it remains crisp even after long boiling. Mainly used in hot pots and soups. Very traditional at Chinese New Year.