Which items are required for the "Polyculture" achievement?

A complete list can be found here on what needs to be shipped:

Spring:

• Parsnip
• Green Bean
• Cauliflower
• Potato
• Kale
• Garlic
• Rhubarb

Summer:

• Melon
• Tomato
• Blueberry
• Hot Pepper
• Wheat
• Radish
• Starfruit
• Hops
• Corn
• Red Cabbage

Fall:

• Eggplant
• Pumpkin
• Bok Choy
• Beet
• Yam
• Cranberry
• Amaranth
• Grape
• Artichoke

In addition, the guide also states strawberries (spring) and coffee beans (spring or summer) or also needed. A user in the comments in the guide (and here) also states that flowers are not necessary (they have been removed from the quote).

"Crop" is anything you can grow from its specific seed, except for flowers, ancient fruits, and sweet gem berries. The full list is:

• Cauliflower
• Coffee bean
• Garlic
• Green bean
• Kale
• Parsnip
• Potato
• Rhubarb
• Strawberry
• Blueberry
• Corn
• Hops
• Hot pepper
• Melon
• Radish
• Red cabbage
• Starfruit
• Sunflower
• Tomato
• Wheat
• Amaranth
• Artichoke
• Beet
• Bok choy
• Cranberry
• Eggplant
• Grape
• Pumpkin
• Yam