Flower:

Spike-like raceme of irregular pale greenish ¼-inch flowers. Sepals and petals are similar; an upper sepal and 2 petals form a hood above, 2 side sepals opened out broadly. The lower lip is broad, with squared sides, a round tip, 2 small side lobes at the base, and near the center of the base a small bump (the tubercle) that blocks insects from entering up the middle, forcing them to enter from the sides. A curved stout spur is below. The flower spike is shorter and more tightly packed in sunny locations, more stretched in the shade.

Leaves and stem:

There are 2 to 3 principal leaves, up to 6 inches long, ¾ inch wide, lanceolate to elliptical, alternately attached, with pointed tips and sheathing at the base. A few short bract-like leaves are on the upper stem. The stem is smooth. Plants are stouter in open sun than in shadier locations.

Notes:

Minnesota is on the northwest edge of this species' range. Rare scattered populations are on the Anoka Sandplain with a few central and southeast Minnesota populations. According to the DNR, much of its habitat is being destroyed by development, mostly around the Metro area. The remaining populations are also threatened by invasive species, woody plants like buckthorn in particular, which kill off the plants by providing too much shade. Tubercled Rein Orchid was added to the Minnesota State Endangered Species list in 1984 but downgraded to Threatened in 2013 after a number of new populations were discovered. This species sometimes goes by Habenaria flava (as in Newcomb's and Peterson's field guides), but genus Habenaria is now widely considered restricted to the tropical species and Platanthera the temperate zone species. Another variety P. flava var. flava, is mostly limited to the southeast U.S. and does not grow in Minnesota.