The bizarre shape of these nuts leaves no room for misidentification. They measure about 2 inches from tip to tip, with a smooth shell as hard as the horns they resemble. The inner nutmeat - as they are sometimes sold shelled - is also wing-tipped but creamy white in color.

Unshelled nuts are difficult to evaluate. Choose that look sound and smell fresh. When cracked, the meat should fill the inner cavity and be uniformly white.

Caltrops, in the shell, may be kept refrigerated for several weeks. Shelled nuts must be eaten within two days of purchase because they decay quickly. Check each nutmeat carefully for soft spots before using.