Flower:

Slender spike-like raceme of 5 to 40 small irregular flowers, about ⅜ inch across, yellowish green in color espcially the lower lip. An upper (dorsal) sepal and two lateral petals form a hood above, 2 oval to lanceolate petal-like sepals spread laterally, often curling back at tips. The lower lip is also lanceolate and about the same size as the lateral sepals. The tip of the lower petal will either open down as the blossom opens or stay touching the tip of the hood above during the entire bloom period. A short, curved club-like spur is behind. Flowers have no fragrance.

Leaves and stem:

Leaves are few to several on a single stem, oblong to lance-linear, up to 9 inches long and 1½ inches wide, sheathing the stem, reducing in size as they ascend the stem, becoming bract-like in the upper plant. Stem, leaf surfaces and leaf margins are hairless.

Fruit:

Fruit is an upright, ridged, elliptical to cylindric capsule containing dust-like seed.

Notes:

Until recently, in Minnesota Northern Green Orchid and  Tall Northern Bog Orchid (Platanthera huronensis) were considered to be  Platanthera hyperborea, also called Northern Green Orchid, but whose range is now considered limited to Greenland and parts of Alaska. There are several easy discriminators between our two species that are helpful when applicable. In Minnesota the range of P. aquilonis completely overlaps the northern boreal forest range of P. huronensis, but it also extends throughout the western and southern prairie regions where P. huronensis has never been encountered (see range maps). Its slender flower spike is rarely ever over 24 inches with a maximum of 40 green to yellowish green flowers on the most robust specimens.  Within the range of P. huronensis, any plants over 24 inches with more than 40 flowers will likely be that species and prompt one to check for a whitish green flower color and fragrance. When plant height and flower number overlap, ID can be a challenge even for experts and requires 10x magnification and a metric ruler. The most precise information for these characteristics can be found in Welby Smith's book “Native Orchids of Minnesota”. For P. aquilonis the lower lip is lance-shaped much like the lateral sepals and measurably shorter, 2.5-5 mm long by 1-1.5 mm wide, than for P. huronensis. There is no dilation of the lip but rather a rounded even taper from base to tip, and the anther sacs are borne somewhat horizontally above the stigma, being closer at the tips and widely separated at their bases. The spur is typically shorter and somewhat club shaped, 2-4.5 mm long. The hood of P. aquilonis also tends to be more flat where P. huronensis is more erect, especially when a flower is in its prime. Flora of North America has a good illustration of the characteristics. The tendency, in many specimens, for the tip of the lower lip to remain adhered to the tips of the upper sepal and petals can make close observation of these traits difficult.