This recent segregate of nigromarginata is known from the mid-Atlantic Coastal Plain (especially Va.) to the Ozarks, and may be expected across much of Ky. (Werier 2006). It is generally reported from more mesic or base-rich soils (usually on mossy banks with thin soil), but further ecological data are needed. Its relatively narrow leaves and short culms also suggest umbellata, but it lacks the more clustered spikes of umbellata and rugosperma (which have frequent basal spikes and lack projecting staminate spikes). C. reznicekii differs from nigromarginata in its mostly narrower widest leaf blades (ca. 1.2-2.2 mm versus 2.3-4.5 mm); its mostly shorter (and often relatively uniform) longest culms (mostly 2-10 cm versus 6-40 cm); its pistillate scales with reddish color usually no more than submarginal (versus often reddish-black from margins to the stripes beside mid-veins); and its somewhat less extensive staminate spikes (usually no more than 3-4 mm above lateral spike apices, versus often up to 5-7 mm).