Americans have been preparing muffins since at least the 19th century, using a wide variety of products to add flavor to the basic batter of flour, sugar and butter (generally not prepared with eggs and by definition unleavened). Fruits and even some garden vegetables have served as flavorings.
Poppy seeds were already popular in most parts of the world for their taste and texture—as well as the narcotic characteristics of the opium poppy plant they are harvested from. As other countries began imitating the American muffin, the occasional use of poppy seeds to flavor them spread as well.
Lemmon poppy muffin mix is sold per 1.36kg box.