This is true, and, as a former botany teacher, I welcome the release of these stamps. These five crops are very important, not only to those of us who live in the Western Hemisphere, but around the world. (We are certainly also indebted to many Old World plants, as well! Thank God for plants from both hemispheres.)
One aspect of the history of these crops is what the King James version of the Bible (1611 AD, before any significant traffic with the New World) does with the word for one particular crop, namely corn. A search of that version for the word "corn" on the Blueletter Bible site returns 102 occurrences in 94 verses, from Genesis 27:28 through 1 Timothy 5:18. Luke 15:15-16 refers to the prodigal son, who wanted to eat from the husks from the food fed to the pigs. Clearly, these references can't have been to Zea mays, the plant most commonly called corn, and the one pictured on the stamps, since this plant did not exist in Bible lands at that time. The word, corn, has these definitions, from the Free Dictionary:
This explains the use of the word in the KJV. The ESV Bible doesn't use the word, corn.
Beans we now use as crops were domesticated in both the New and Old Worlds, some types in one place, some in another. The Sunflower genus of plants are apparently all from the New World. So are the plants usually called chili peppers, and those called squashes, although all three of these plants have Old world relatives, found in the same plant families. (In case you've forgotten, or never knew, a family, such as the pea family, usually contains more than one genus, and a genus usually contains more than one species. The scientific name of an organism, such as Zea mays, consists of its genus and species name. Common names are fine, but since they vary between locations and cultures, to say nothing of between language groups, their use can confuse.)
Thanks for reading!