Spiranthes is a genus of orchids in the subfamily Orchidoideae. They are known commonly as ladies tresses, ladies'-tresses, or lady's tresses. The genus is distributed in the Americas, Eurasia, and Australia. The genus name Spiranthes is derived from the Greek speira ("coil") and anthos ("flower"), and was inspired by the spirally arranged inflorescence. Description These are perennial herbs growing from fleshy root systems that range from slender to tuberous, and are occasionally stoloniferous. Most of the leaves are basal, but some species have leaves higher on the stem before the inflorescence matures, often taking the form of a sheath around the stem. The inflorescence is a terminal spike with flowers arranged in a characteristic loose or dense spiral. As in most other orchids, the flowers are resupinate, twisting during development into an upside-down position. The six tepals may be separate, or the three upper may be joined to form a hood over the lip petal. The lip is thin to somewhat fleshy, and two basal glands produce nectar. The flowers are usually white, cream, ivory, or yellowish, and two species have pink flowers; a few are also fragrant. Taxonomy and naming The genus Spiranthes was first formally described in 1817 by Louis Claude Richard in his book De Orchideis Europaeis Annotationes. The genus's name is derived from ancient Greek words meaning "a coil" and "a flower". Since its original description, the genus has undergone many taxonomic changes. Spiranthes once contained all the species from the subtribe Spiranthinae. In 1920, Spiranthes was split into 24 genera. Revisions in 1951 and 1958 placed more species into the genus. During the 1990s it was divided again. Spiranthes has recently received increased attention from taxonomists and systematists, leading to new species discovery and the resolution of many long-term taxonomic questions. It is difficult to clearly define some of the species of this taxon because some of them are polymorphic, taking a number of different forms, with some species belonging to species complexes involving several closely related and morphologically similar species (e.g., the S. cernua species complex; S. parksii, a member of the S. cernua complex and probably a descendant of S. cernua. It has been suggested that this species is just another rare form). Species list The following is a list of species accepted by the World Checklist of Selected Plant Families as at May 2020: Spiranthes aestivalis (Poir.) Rich. (1817) – summer-flowering spiranthes