Mishna Peah Chapter 1, Mishna 4:
כלל אמרו בפאה. כל שהוא אוכל, ונשמר, וגידוליו מן הארץ, ולקיטתו כאחת, ומכניסו לקיום, חייב בפאה. והתבואה והקטניות (1) בכלל הזה.
First principle, fruits that must met five criteria.
- Food, => not plants for the production of dyes,
- In a guarded place, => not wild plants,
- Grows on the ground, => not mushrooms and truffles,
- Harvested at one time, => not figs,
- Earned, => not fresh vegetables.
(1): After the rule, the mishna enumerates examples, tevua, it's the five species of cereal, kitnit, it's non cereal consumable seeds, and further in the next mishna tree fruits. It seems useless. The Melechet Shelomo explains that it's an allusion for the hermeneutic basis of the rule. Indeed, the Talmud Yerushalmi explains that
ובקוצרכם אין לי אלא תבואה קטניות מנין ת"ל ארצכם אלנות מנין ת"ל שדך
Kutsrechem for 5 cereals, Artsechem for kitniot, Sadecha for tree fruits. See Rabenu Shimshon for an extensive explanation and different degrees of duty, rabbinical and scriptural.