15. Spiranthes Rich. (ladies’ tresses)
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.
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.
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.
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.
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.