Spiranthes spiralis

Species of orchid

Spiranthes spiralis, commonly known as autumn lady's tresses, is an orchid that grows in Europe and adjacent North Africa and Asia. It is a small grey green plant. It forms a rosette of four to five pointed, sessile, ovate leaves about in length. In late summer an unbranched stem of about tall is produced with approximately four sheath shaped leaves. The white flowers are about long and have a green spot on the lower lip. They are arranged in a helix around the upper half of the stalk. The species is listed in Appendix II of CITES as a species that is not currently threatened with extinction but that may become so. Autumn lady's tresses are legally protected in Belgium and the Netherlands, and in some regions of France.

Autumn lady's tresses is a polycarp, perennial, herbaceous plant that remains underground during its dormancy in summer with tubers. The species has thirty chromosomes (2n=30).

Outer tepals are oblong ovate, slightly tapering to a blunt tip, long, white with a light green vein, have a ciliate or very finely serrated edge, and on the outside with little glandular hairs. Inner perianth leaves are white, elongate with a blunt tip, a vein and adhere with the slightly longer upper outer perianth leaf, thereby forming an upward decurved upper lip. The lower lip is pale green with a wide irregular jagged edge of crystal like transparent white growths, oblong, approximately long and 2½–3 mm (0.10–0.12 in) wide, trough shaped, rounded and without lobes and at its top bending down. Both lips give the flower as a whole a trumpet shape. The lower lip encloses the column (merger of the stamen and style) at the base, and there are also two white, glossy, round, nectar secreting glands, each with a ring of papillae around their base. The small column is green.

In 1753, Carl Linnaeus was the first to correctly describe the species in his Species Plantarum, naming it Ophrys spiralis. In 1827, François Fulgis Chevallier moved it to the genus Spiranthes that had been erected by Louis Claude Richard in 1817. Synonyms include O. autumnalis, Epipactis spiralis, Serapias spiralis, Neottia spiralis, N. autumnalis, Ibidium spirale, Gyrostachys autumnalis, Spiranthes autumnalis and S. glauca. Autumn lady's threshes belongs to a genus with many species in North America, but only three species occur in Europe.

Recent DNA analysis showed that three Eurasian species of Spiranthes are most related to each other, with a clade consisting of S. sinensis and S. aestivalis being the sister group of S. spiralis.

The botanical name is derived from the ancient Greek σπεῖρα (speira) "spiral" and ἄνθος (anthos) "flower". The species name spiralis also refers to the placement of the flowers in a spiral.

Autumn lady's tresses occurs in Europe and small adjacent parts of North Africa and Asia. In the west, it occurs from Ireland to Portugal, in the south from Spain including the Balearic Islands, the coastal mountains of Algeria, Italy including Sicily, Greece including Crete, the Mediterranean, Aegean and Black Sea Coasts of Turkey and the Caucasus Mountains, North Iran eastwards to the Western Himalayas. To the North its limit is from northern England, the Netherlands, Denmark and the southern Baltic, Poland to western Ukraine. It is now considered regionally extinct in Denmark, but it has been introduced to the Swedish island of Öland, where it now seems to be established. In Switzerland the most recent locations are around Lake Lucerne, the Rhine Valley near Chur, in the area of Lake Walen and in Ticino. In Italy it is found in the north east near the sea. In Great Britain and Ireland its northernmost occurrence is on the Isle of Man. It has never been found in Scotland. In Ireland it has a scattered southern distribution north to County Sligo, with the only known colony in Northern Ireland discovered in 2023 in County Down. In Germany, the plant is endangered in Bavaria (Franconian Heights and Franconian Jura) and Hesse, very endangered in Baden Württemberg (Swabian Jura and foothills of the Alps) and Rhineland Palatinate, and near extinction in Saxony Anhalt, Thuringia and Lower Saxony. In France, it occurs across the country, except for the regions of Champagne Ardenne and Lorraine, and the departments of Nord, Aisne, Eure, Bas Rhin, Val d'Oise and Seine et Marne. It is relatively common on the coasts of Brittany and the Provence, and in the valley of the Orne. The original range of S. spiralis is probably Mediterranean. Only when man created the habitat for this orchid by settling and converting forests to agriculture and animal husbandry, the species could spread to the north (7000 to 4000 BC).

It grows in dry grassy places such as meadows, garigue, heaths, and pine woodland, generally on calcareous soils.

Autumn lady's tresses may be found on quite different substrates, from weathered chalk and limestone to sand and gravel in dunes and slightly acidic heathlands. Occasionally, it has also been found on clay on sloping sites. It sometimes occurs in lawns, and was reported from the top of a wall in Sicily. Soils need to be low in nitrogen and phosphorus and neither dry nor wet. The species occurs in different plant communities, most commonly in highly diverse Festuca ovina–Avenula pratensis grasslands that exist because of intense grazing by sheep or rabbits. These grasslands contain grasses, dicots, and mosses in different mixtures. The turf is short, continuous and consist of very small individual plants. Characteristic species that may be abundant in these grasslands in the UK include the grasses Sheep's fescue Festuca ovina, red fescue F. rubra, Quaking grass Briza media, crested hair grass Koeleria macrantha and Crested dog's tail Cynosurus cristatus, the dicots ribwort plantain Plantago lanceolata, Small burnet Poterium sanguisorba ssp. sanguisorba, Common Bird's foot Trefoil Lotus corniculatus, Common Cat's ear Hypochaeris radicata, Mouse ear hawkweed Pilosella officinarum, Rough hawkbit Leontodon hispidus and Dwarf thistle Cirsium acaule, and the moss Pseudoscleropodium purum. In the Netherlands, the remaining population in an old dune grassland occurs in a community akin to the Botrychio Polygaletum, where it occurs with Briza media, Glaucous sedge Carex flacca, Broad leaved thyme Thymus pulegioides, Common milkwort Polygala vulgaris and Fairy flax Linum catharticum.

Pollination of autumn lady's tresses is little observed. In the Netherlands the common carder bee (Bombus pascuorum) and red tailed bumblebee (Bombus lapidarius) are regular visitors. In southern France (Rhône Department) the honeybee also pollinates. The silver Y (Autographa gamma) is also seen to visits the flowers, but attached pollinia have not been observed. In 52% of the plants the flowers are arranged counterclockwise, in 39% clockwise and in 9% of the plants the flowers are to one side of the inflorescence. The pollinators always land at bottom of the inflorescence and visit the flowers ever higher up. Most bumblebees have a strong preference for counterclockwise arrangement, fewer for clockwise. It seems that autumn lady's tresses responds to this preference by offering different inflorescence types and thus increases the chances of fertilization.

The rust Uredo oncidii is known to infect the leaves and stems of Spiranthes spiralis.