3,041. Similar-Looking Trees

Hilchos Kilayim 3:4

The ideas in the preceding halachos also apply to trees: some kinds of trees may have leaves or fruit that are similar, but they’re kilayim with one another because they’re still separate species. Examples of this include apples and crabapples, peaches and almonds, and plums and jujube; all of these pairs look similar but are kilayim with one another. Apricots and white plums are not kilayim with one another, nor are quince and hawthorn.

Hilchos Kilayim 3:5

There are plants and trees that the Sages weren't concerned about vis-à-vis kilayim even though they’re different species because the leaves or the fruit of one resemble those of the other so much that they appear to be variants of the same species. The idea is that when it comes to kilayim we rely on how things look.