Lemon, Citrus
The lemon is characterized by its yellow, sunny color and distinctive taste; it is full of vitamins, all of which give it associations with "liveliness," and perhaps also sharpness and clarity.
In Jewish, Christian, and Roman traditions, it is associated with love and marriage; in alchemy, the lemon (and orange) was used as a symbol of the sun. However, it is also sour, which may hint at something difficult to sink one's teeth into.
A key feature of citrus fruits, in contrast to apples and pears, for example, is that they have a very thick peel that protects a very soft interior.