Spiranthes diluvialis

Ute Ladies' Tresses is a perennial orchid with usually 1 stem that is 20-50 cm tall and arising from tuberously thickened roots. Its narrow leaves are 1 cm wide, can reach 28 cm long, are longest at their base, and persist during flowering. The inflorescence consists of few to many white or ivory flowers clustered in a spike of 3-rank spirals at the top of the stem. The sepals and petals are ascending or perpendicular to the stem. The lateral sepals often spread abruptly from the base of the flower, and sepals are free or only slightly connate at the base. The lip petal is somewhat constricted at the median.

Spiranthes diluvialis has characteristics intermediate between S. romanzoffiana and S. magnicamporum. Adapted from Fertig et al. (2005): S. diluvialis is distinguished from S. romanzoffiana by its whitish, stout, ringent (gaping at the mouth) flowers, by its oval to lance-shaped, narrowed-at-the-middle lip petal with crispy-wavy margins that is exposed in lateral view (compared to the deeply constricted, fiddle-shaped lip petals of S. romanzoffiana), by its sepals being free or connate at the base for a short distance rather than fused to form a hood above the lip, and by its sparsely pubescent inflorescence (S. romanzoffiana has pubescence of short hairs along the stem and inflorescence). S. romanzoffiana occurs in montane wetlands (up to 3400 m) throughout the Rocky Mountains. S. magnicamporum and S. cernua have strap-shaped, wavy-margined lip petals (compared to S. diluvialis' oval to lance-shaped, narrowed-at-the-middle lip petal with crispy-wavy margins), lack leaves at flowering time (leaves of S. diluvialis persist at flowering time), and occur in low-elevation (to 1900 m) wetlands of the Great Plains east of the known range of S. diluvialis (except in Nebraska). S. porrifolia has pale yellow flowers with sepals fused for about half their length but not forming a hood (compared to the white flowers with sepals free or connate for a short distance of S. diluvialis), strap-shaped lip petals with peg-like hairs on the upper surface (compared to S. diluvialis' oval to lance-shaped, narrowed-at-the-middle lip petal with crispy-wavy margins), and glabrous stems. It occurs primarily along the Pacific Coast inland to Idaho and western Nevada in wetlands from 100-2600 m. S. infernalis has yellowish-white flowers with a green lip that is widest near the middle before tapering to the base and is endemic to the Ash Meadows of southern Nevada.
From CNHP Wetland Guide 2012:
Main Characteristics:
·Tepals distinct or united only at the base, not forming a hood above the lip, outer lateral tepals spreading
·Flowers diverging at about a 90 degree angle or higher from rachis
·Inflorescence looser, rachis usually visible

This species is adapted to early- to mid-seral, moist to wet conditions, where competition for light, space, water, and other resources is normally kept low by periodic or recent disturbance events. Major occupied habitat types include (1) alluvial banks, point bars, floodplains, or ox-bows associated with perennial streams, with a high water table and short, perennial graminoid- and forb-dominated vegetation maintained by grazing, periodic flooding, or mowing; (2) river floodplain habitats which experience regular spring flooding and/or frequent large scale floods but maintain relatively stable, moist to wet soil in summer, within moist meadow, riparian woodland, or riparian shrubland communities; (3) shores of lakes and reservoirs, in mesic meadow-type vegetation maintained by lake level fluctuations or seasonal flooding of gravel bars; (4) groundwater-fed springs, sometimes in desert settings, or sub-irrigated meadows where edaphic characteristics (e.g. high water table and calcic soil), fire, and/or grazing are sufficient to prevent invasion of later seral vegetation; and (5) human-influenced habitats, including perennial stream, river, lakeshore, and spring sites directly associated with human-developed dams, levees, reservoirs, irrigation ditches, reclaimed gravel quarries, roadside barrow pits, and irrigated meadows. More than half of documented populations occur in sites in which natural hydrology has been influenced by dams, reservoirs, or supplemental irrigation, and many populations occur within agricultural or urban settings. 550 - 2100 m. (adapted from Fertig et al. 2005)

Across its range Spiranthes diluvialis blooms from early July to late October. Asynchronous maturation of flowers promotes outcrossing, but flowers are self-compatible (Fertig et al. 2005).