Spinach is a name used for leafy green vegetables. The true spinach that you commonly find in a U.S.A. grocery store has the scientific name: Spinacea oleracea. However, there are other species of edible leafy greens that have been given the name spinach, even though they are not related to the true spinach. These plants are similar to spinach and work well as a spinach substitute. True spinach prefers to grow in cooler weather and does not grow during hot summers. Many of the spinach substitutes thrive in the heat and are grown during hot summers when spinach will simply not grow.