I say it's spinach

(Broccoli was a relative novelty at that time, just then being widely introduced by Italian immigrant growers to the tables of East Coast cities.

[4]) What White called "the spinach joke"[5] quickly became one of the New Yorker cartoon captions to enter the vernacular (later examples include Peter Arno's "Back to the drawing board!"

[6] For instance, Alexander Woolcott in his 1934 collection While Rome Burns: "This eruption of reticence... will, I am sure, be described by certain temperaments as an exercise in good taste.

[13] The same phrase, although with unclear meaning, is also seen in the nursery rhyme "A Frog He Would A-Wooing Go" ("With a rowley, powley, gammon and spinach/heigh ho!

[14] The 1989 second edition of the Oxford English Dictionary lists these two close senses as letters below the same number in the entry for "spinach".