This word is acceptable for play in the US & UK dictionaries that are being used in the following games:

• Lexulous
• Wordscraper
• Wordosaur

n. Plural form of arboretum.

"Public gardens, such as arboreta and botanical gardens, often do a splendid job educating and inspiring the public in ornamental horticulture; their offerings in food gardening tend to be more limited."