This is a largely Appalachian taxon that probably deserves species status. An 1837 coll. by C.W. Short (GH) is labelled: "Oenothera fruticosa var. ambigua Nuttall. So says Dr. Torrey--It is the most beautiful of our species, and not vespertine [flowering at night]. In the mountains of Ky. June." But there has been much confusion with typical tetragona, brevistipata and fruticosa, partly due to complex nomenclature and conflicting treatments; see notes under those names. O. glauca and close allies in the tetragona group may all be tetraploids (2n = 28), while the fruticosa group is tetraploid, hexaploid or octoploid (Cr, Y). However, Wagner (2014; and FNA in prep.) has combined glauca with tetragona as O. fruticosa ssp. tetragona (Roth) W.L. Wagner. O. glauca differs from typical tetragona (including longistipata) as follows (F, W): petals mostly 2.5-3.5 cm long (versus 1.2-2 cm); cauline leaves mostly 1-3 cm wide (versus 0.5-1 cm), with 1-4 teeth per 2 cm of margin (versus 4-6), often glaucous beneath (versus not glaucous); plants glabrous throughout (versus pubescent to glabrescent). However, there may be intermediate populations, such as on rocky river banks in MCRE; see notes under tetragona. Both taxa together differ from fruticosa (sensu stricto) plus brevistipata (and close allies) as follows (W): capsules oblong, widest near middle (versus clavate, widest above middle), usually abruptly tapered to a stipe 0.1-3 (-7) mm long (versus gradually tapered to 3-10 mm stipe); hairs of ovary and capsule predominantly glandular or the ovary glabrous (versus with nonglandular hairs or mixed); leaves subglabrous or sparsely pubescent (versus generally pubescent), more or less dentate (versus subentire).