菱 is "water chestnut", a nut that actually is spiky, the <> figures are a stylization of that. 菱形, that is, "water chestnut-shaped" is indeed used for what's c

菱 is "water chestnut", a nut that actually is spiky, the <> figures are a stylization of that. 菱形, that is, "water chestnut-shaped" is indeed used for what's called "diamond-shaped" in English, maybe hence the confusion.