Its leaves grow in a single whorl below a flower growing in two whorls. The purplish flowers are placed in close whorls on elongate racemes. Flowers have six stamens in two whorls of three, which persist after fruiting. The perianth (perigonium) consists of six undifferentiated tepals arranged in two whorls of three. Basal, medial, and apical whorls of hairs occur on the antennal segments. Perianths&colon; six tepals divided into two whorls, free or joined (connate). Gynoecium tricarpellate, ovary epigynous (inferior), two trimerous androecial whorls with stamens 6, 5 or 1. The leaves of horsetails are arranged in whorls fused into nodal sheaths. The perianth-segments are in two whorls of three. Growing immersed in fresh water, they consist of a central stalk with whorls of branchlets. They contain numerous sporophylls arranged in whorls or spirals. In later lineages, carpels tend to be in whorls. These are concentric, layered whorls of epithelial cells that increase in number throughout life. When the perianth is in two whorls, it is described as biseriate. It has 18 double-crested caudal whorls and 17 single-crested caudal whorls.