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Published In: De Orchideis Europaeis Annotationes 28–29, 36–37. 1817. (Aug.-Sept. 1817) (De Orchid. Eur.) Name publication detail
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 7/23/2009)

 

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15. Spiranthes Rich. (ladies’ tresses)

Plants lacking rhizomes, the roots fascicled from the base of the flowering stem, sometimes thickened and tuberlike. Flowering stems with dense terminal spikes of narrow, cylindrical to broadly urn‑shaped flowers. Leaves several, green, basal, those of the flowering stems reduced to small sheathing bracts. Sepals and lateral petals similar, linear to lanceolate. Lip ovate to oblong, with 2 small conical protuberances on either side of the base. Stamen 1, staminodes lacking. Capsules ascending, 4–10 mm long, elliptic in outline, with longitudinal lines or ribs. Thirty species, nearly worldwide, but most diverse in North America.

The generic boundaries are still hotly debated by orchidologists. A conservative classification would combine about 35 segregates into Spiranthes, and the genus in the broad sense contains about 300 species.

The species of Spiranthes in Missouri all have the flowers in a single spiral in the inflorescence. However, in some taxa the spiral is so tight and each loop of flowers around the axis occupies so little vertical space that the overall appearance presents the illusion of two or more vertical ranks or intertwined spirals. Sometimes the spiral nature of the flowers is not discernable at all in such plants.

Species determination in Spiranthes can be challenging, especially from dried, pressed specimens. The relative positions of the perianth parts and details of lip coloration are most easily observed from living plants in the field. In all species, the flowers are progressively smaller toward the tip of the inflorescence. The size measurements cited in the species treatments refer to fully formed flowers in the lower half of the spike.

The common name is believed to have arisen because the spiral arrangement of the flowers was thought to resemble a woman’s braided hair. The spiral pattern of flowers is thought to be an adaptation to bee pollination, and most of the species are pollinated by various bees, from bumblebees to honeybees and smaller, native bees.

 

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1 Sepals and lateral petals 6–11 mm long (2)
+ Sepals and lateral petals 3.5–7.0 mm long (4)
2 (1) Axis of the inflorescence with dense, short, nonglandular hairs, the flowers appearing as a single spiral along the flowering stems; flowering stems 50–100 cm long 7 Spiranthes vernalis
+ Axis of the inflorescence with sparse to dense, glandular hairs, the flowers appearing as though in 2 or more intertwined spirals along the flowering stems (sometimes no spirals are discernable); flowering stems mostly 10–50 cm long (3)
3 (2) Lateral sepals only slightly spreading, oriented parallel to the rest of the perianth 1 Spiranthes cernua
+ Lateral sepals spreading, the tips arching upward and angled away from the rest of the perianth 4 Spiranthes magnicamporum
4 (1) Sepals fused in the basal 0.5–1.0 mm; lip white with an orange-yellow to yellow area in the middle of the inner surface 3 Spiranthes lucida
+ Sepals free to the base; lip all white or with a green area in the middle of the inner surface (5)
5 (4) Flowers appearing as though in 2 or more ranks or intertwined spirals along the flowering stems (sometimes no spirals are discernable) 5 Spiranthes ovalis
+ Flowers appearing as a single spiral along the flowering stems (6)
6 (5) Lip white with a green area in the middle of the inner surface, this usually darkened when dry; axis of the inflorescence with sparse to dense, glandular hairs 2 Spiranthes lacera
+ Lip all white; axis of the inflorescence glabrous 6 Spiranthes tuberosa
 
 
 
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