Comparison of Carex pellita and Carex lasiocarpa

Carex pellita and Carex lasiocarpa are closely related. 

1. Sedges (Carex) of Saskatchewan, Fascicle 3, Flora of Saskatchewan by Anna Leighton distinguish between the two species as follows:

C. pellita - leaves 2-3 (6) mm wide, flat
C.  lasiocarpa - leaves less than 2.2 mm wide, involute to rolled

2. Flora of North America distinguish them as follows:

C. pellita - Leaf blades flat or folded into an M shape except at base and near tip, (2–) 2.2–4.5 (–6) mm wide, not prolonged into long filiform tip; leaves and proximal bract with midvein forming prominent, sharply pointed keel for much of length.
C. lasiocarpa - Leaf blades involute to triangular-channeled, 0.7–2(–2.2) mm wide, those of vegetative shoots especially long-prolonged into curled, filiform tip; leaves and proximal bract with midvein low, rounded, forming inconspicuous keel (at least proximally).

3. Genetic Differentiation Between Carex lasiocarpa and C. pellita (Cyperaceae) in North America by Katherine A. McClintock and Marcia J. Waterway in American Journal of Botany 81(2): 224-231, 1994 provides the following (somewhat edited by myself) discussion:

"Carex lasiocarpa and C. pellita are two closely related and structurally similar rhizomatous sedges, characterized by their densely pubescent, short-beaked perigynia.  The two species can be distinguished from each other by the shapes of their culms and leaves, with C. lasiocarpa having terete culms and involute leaves with an indistinct midvein, while C. pellita has more triangular culms and flat leaves with revolute margins and a prominent midvein.  Carex lasiocarpa is circumpolar in distribution, while C. pellita is restricted to North America, where the two species have different, but broadly overlapping, geographic ranges.  The habitat of the two species differ very markedly.  Carex lasiocarpa is typically found in bogs and minerotrophic fens with a water pH of 3.6 to 6.7 and calcium concentrations from 0.5 to 13.8 mg/liter, but it is also a member of emergent marsh communities in both eastern and western Canada.  In contrast, the habitat of C. pellita is sunny swampy places, mostly in calcereous soils.  C. pellita can be found on sandy or marly shores, marshes, meadows, swales, riverbanks, and rarely in dry sandy woodland."

"Clausen and Wahl (1939) considered C. pellita as a subspecies of C. lasiocarpa, based in part on their observations of continuous variation in structural characters such as leaf width, peduncle length, and the shape of the pistillate scales in the region where the two taxa are sympatric."

The authors studied the morphological differences between the type specimens as well as allozyme variation and chromosome numbers.  They concluded that C. pellita and C. lasiocarpa are in fact different species.  They suggested C. pellita may be a daughter species still in the process of divergence from C. lasiocarpa.