TETRANDRIA, (τετρανδρία "four," and άνδρες "a man or husband"); the name of the fourth class in Linnæus's Sexual System, consisting of plants with hermaphrodite flowers, which have four stamens or male organs that are of equal length. In this last circumstance consists the main difference, according to Linnæus, between the plants of the class in question and those of the 14th class, didynamia, in which the four stamens are of unequal length, two of them being long, and two short.—The orders in this numerous class are three, founded upon the number of styles or female organs. Scabious, teazel, barren-wort, the starry plants of Ray, and the greater number of genera in this class, have one style; dodder, and hyacinth have two; holly, and a few others, have four.