7. Platanthera praeclara Sheviak & M.L. Bowles (western prairie fringed orchid)

Pl. 116 f, g; Map 478

Habenaria leucophaea (Nutt.) A. Gray var. praeclara (Sheviak & M.L. Bowles) Cronquist

Flowering stems 25–85 cm long, the flowers 8–18 in a dense raceme. Main stem leaves 3–6. Sepals 11–13 mm long, the upper sepal slightly shorter than the lateral ones, light creamy white, usually greenish tinged toward the base. Lateral petals 10.5–15.0 mm long, broadly obovate to broadly spathulate, the tips cut straight across or shallowly indented, sharply toothed or with a short fringe, light creamy white. Lip 19–32 mm long, 3‑lobed, the lobes broadly fan‑shaped, deeply fringed, light creamy‑white. Spur 36–55 mm long, 2.0–3.2 mm in maximum diameter. Column 5.5–7.5 mm long, white, the viscidia 6.2–7.5 mm apart, positioned so as to face forward (more or less parallel to each other). 2n=42. June–July.

Uncommon, known from mostly historical collections in western Missouri (Wyoming to Minnesota south to Oklahoma, almost exclusively in the Great Plains). Mesic portions of upland prairies and bottomland prairies, often on calcareous substrates or on loess‑derived soils.

As with its eastern counterpart, P. leucophaea, this beautiful orchid has been extirpated throughout a large portion of its former range because of the plowing of many prairies and the overgrazing of others. It also is presently listed as Threatened by the U.S. Fish and Wildlife Service under the federal Endangered Species Act. The few extant stations for this species are all in northwestern Missouri, and all occur in mesic upland prairies on loess‑derived soils. Invasion of these prairies by woody plants appears to be the most significant threat to the populations, aside from the continued threat of the plow.

The eastern and western prairie fringed orchids were first separated and characterized by Sheviak and Bowles (1986). Although superficially similar morphologically, producing similar, sweet fragrances, and pollinated nocturnally by species of sphinx moths, these two beautiful orchids have sufficiently different pollination syndromes that hybridization in nature is unlikely. The closely placed, inwardly facing viscidia of P. leucophaea deposit pollinia on a different portion of a potential pollinator’s eyes or proboscis than do the more broadly spaced, outwardly facing viscidia of P. praeclara.

Other morphological trends also serve to separate the two taxa. Inflorescences of P. praeclara tend to be shorter, more densely flowered, and fewer flowered than are those of P. leucophaea, and the flowers of the former tend to be larger, with longer sepals and spurs. There are also subtle differences between the two species in lateral petal shape and perianth color.