Spiranthes, commonly called Ladies'-tresses, is a genus of orchids (family (Orchidaceae) belonging to the subfamily Orchidoideae.
It has a very wide, almost continuous distribution, mostly in temperate zones of the northern hemisphere: Europe, North Africa, Asia, Australia, New Guinea, the Americas and the Caribbean. It is a provincially endangered orchid, in North America it can be found in Manitoba, Ontario and more than 20 American states. They grow in meadows, fields and savannas but are also found in forests, both on acid and calcareous soil. Most species tend to become weeds in disturbed areas, while they may be scarce in undisturbed areas.
Plants can grow to a height of 12 to 38 cm (4.5 to 15 inches). Spiranthes consists of perennial, terrestrial orchids with clustered, tuberous or rarely fibrous, fleshy roots. The leaves are basal or occasionally cauline (i.e. emerging from the stem). They are variable in shape. They range from broadly ovate to elliptic, or absent at flowering.
The flowering stem has foliaceous sheaths. The stem is erect and spiraling (as the name Spiranthes indicates). It carries persistent, sheathing bracts. The resupinate, tubular flowers are arranged in a more or less spirally twisted, showy or inconspicuous terminal spike. Their color is typically a shade of white or yellowish-white or even pink (as in Spiranthes sinensis).
This genus has undergone many taxonomic changes: originally Spiranthes contained all the species from the subtribe Spiranthinae. In 1920 Schlechter divided this genus in 24 genera. A revision by Williams in 1951 and by Schweinfurth in 1958, inflated the number of species of this genus again. Finally D. Szlachetko, with several studies in the 1990s, divided this genus in several genera, contained in 3 subtribes. During all these changes, there is only one species that has remained taxonomically unchanged: Spiranthes parksii
Spiranthes is derived from the Ancient Greek σπεῖρα (twisted or coiled) and ἄνθος (flower).
Flowers of this genus are commonly popular in Japan, where it is called nejibana (捻花^?) (lit.twisting flower.)

Species

• Spiranthes aestivalis (Poir.) Rich. (1817) : Summer-flowering Spiranthes (Western & Central Europe to NW. Africa)
• Spiranthes angustilabris J.J.Sm. (1913) (New Guinea)
• Spiranthes brevilabris Lindl. (1840) : Texas Ladies'-tresses (SE. U.S.A. to East Texas)
  • Spiranthes brevilabris var. brevilabris
  • Spiranthes brevilabris var. floridana (Wherry) Luer (1972).
• Spiranthes casei Catling & Cruise (1974 publ. 1975) : Case's ladies'-tresses (Eastern Canada to NE. U.S.A.)
  • Spiranthes casei var. casei
  • Spiranthes casei var. novaescotiae Catling (1981) (Nova Scotia)
• Spiranthes cernua (L.) Rich. (1817) : Nodding Ladies'-tresses (Eastern Canada to Central & Eastern U.S.A.)
• Spiranthes delitescens Sheviak (1990) : Reclusive Ladies'-tresses (Arizona)
• Spiranthes diluvialis Sheviak (1984) : Ute's Ladies'-tresses (NW. U.S.A. to Nebraska)
• Spiranthes eatonii Ames ex P.M.Br. (1999) : Eaton's Ladies'-tresses (SE. U.S.A. to E. Texas)
• Spiranthes graminea Lindl. in G.Bentham (1840) : Canelo Ladies'-tresses (Arizona, Mexico, Honduras, Nicaragua)
• Spiranthes hongkongensis S.Y.Hu & Barretto (1976)(Hong Kong)
• Spiranthes infernalis Sheviak (1989): Ash Meadows Ladies'-tresses (Nevada)
• Spiranthes lacera (Raf.) Raf. (1833) : Northern Slender Ladies'-tresses (C. & E. Canada to C. & E. U.S.A)
  • Spiranthes lacera var. gracilis : Slender Ladies'-tresses (Bigelow) Luer (1975) (S. Ontario to C. & E. U.S.A.)
  • Spiranthes lacera var. lacera
• Spiranthes laciniata (Small) Ames (1905): Lace-lipped Ladies'-tresses (New Jersey to E. Texas)
• Spiranthes longilabris Lindl. (1840) : Giant-spiral Ladies'-tresses (SE. U.S.A. to E. Texas)
• Spiranthes lucida (H.H.Eaton) Ames (1908) : Shining Ladies'-tresses (SE. Canada, NC. & E. U.S.A.)
• Spiranthes magnicamporum Sheviak (1973) : Great Plains Ladies'-tresses (S. Canada to C. & EC. U.S.A.)
• Spiranthes nebulorum Catling & V.R.Catling (1988) (Mexico, Guatemala)
• Spiranthes ochroleuca (Rydb.) Rydb. (1932) : Yellow Nodding Ladies'-tresses (SE. Canada to E. U.S.A.)
• Spiranthes odorata (Nutt.) Lindl. (1840) : Fragrant Ladies'-tresses, Marsh Ladies'-tresses (SE. U.S.A. to SE. Oklahoma)
• Spiranthes ovalis Lindl. (1840) : October ladies'-tresses (Ontario to EC. & SE. U.S.A.)
  • Spiranthes ovalis var. erostellata Catling (1983).
  • Spiranthes ovalis var. ovalis
• Spiranthes parksii Correll (1947): Navasota Ladies'-tresses (Texas)
• Spiranthes porrifolia Lindl. (1840) : Leek-leaved Ladies'-tresses, Creamy ladies'-tresses (W. USA)
• Spiranthes praecox (Walter) S.Watson in A.Gray (1890) : Early-blooming Spiranthes, Green-vein ladies'-tresses (New Jersey to E. Texas)
• Spiranthes pusilla (Blume) Miq. (1859) (Sumatra)
• Spiranthes romanzoffiana Cham. (1828) : Hooded Ladies'-tresses (Great Britain, Ireland, Subarctic America to N. & WC. U.S.A)
• Spiranthes sinensis (Pers.) Ames (1908) : Chinese Spiranthes (E. European Russia to Pacific, Borneo, Java, Sumatra, Philippines, Australia, Tasmania, New Zealand, New Guinea, Samoa, Vanuatu)
  • Spiranthes sinensis f. autumnus Tsukaya (2005) (Japan)
• Spiranthes spiralis (L.) Chevall. (1827) : Autumn Ladies-tresses, Spiraled Spiranthes (Europe, Mediterranean to W. Himalaya)
• Spiranthes torta (Thunb.) Garay & H.R.Sweet in R.A.Howard (1974): Southern ladies'-tresses (Florida, Caribbean, Mexico, Central America)
• Spiranthes tuberosa Raf. (1833) : Little Ladies'-tresses (E. & EC. U.S.A)
• Spiranthes vernalis Engelm. & A.Gray (1845): Spring Ladies'-tresses (Quebec, E. & EC. U.S.A, Mexico, Guatemala, Bahamas)

Division into species and hybrids

Since the species do not readily cross with each other, hybrids are rare in this genus.

• Spiranthes × intermedia Ames (1903) (SE. Canada to NE. U.S.A.)
• Spiranthes × itchetuckneensis P.M.Br. (1999) (Florida)
• Spiranthes × simpsonii Catling & Sheviak (1993) (SE. Canada to NC. U.S.A)

Dr. Charles Sheviak, a taxonomist with the New York State Museum, has suggested that Spiranthes delitescens is an amphiploid hybrid between two species with different chromosome numbers, possibly Spiranthes vernalis and Spiranthes porrifolia Sheviak (1990) (Arizona).

Spiranthes spiralis in its habitat

However, more complicated forms of gene flow are present in this genus. There are a number of polyploid species known as the S. cernua complex, which are characterized by apomixis and polyembryony. This complex includes S. cernua, S. parksii,^[1] and perhaps S. casei.^[2] Related species, which include at least some plants identified as S. magnicamporum, S. ochroleuca, and S. odorata, are diploids and there is gene flow from the diploids to the polyploids, but not in reverse.^[2]