Explanation by @arethusa

S. ovalis is a small plant with tiny flowers. More significantly, the lateral sepals are generally more separated from the petals and the labella are white or sometimes centrally yellow. S. odorata is actually the largest Spiranthes species in the United States and Canada, has lateral sepals which diverge little from the petals, and has labella which are centrally yellow or yellowish-green. The central yellow-green coloration isn't usually very strong, but it is visible in your photos if you look closely.

Posted on October 13, 2022 05:11 PM by amypadgett