Spikes:

Separate staminate (male) and pistillate (female) spikes, with a single staminate spike to 1+ inches long at the top of the stem, or more frequently a bit longer with pistillate flowers at the tip (gynecandrous). Below the terminal spike are 3 to 7 erect to ascending all-pistillate spikes arising singly from the nodes, most of which are in close proximity to the terminal spike but the lowest may be more distant. Pistillate spikes are short-stalked to stalkless, slender and cylindrical, up to 2½ inches long, each with a leaf-like bract at the base of the stalk, the bract of the lowest spike consistently over-topping the terminal spike.

Leaves and stems:

Leaves are basal and alternate on the lower stem, 4 to 9 leaves per stem, 1.5 to 3.5 mm wide, frequently over-topping the flowering stem. Stem leaf sheaths loosely wrap the stem, are translucent whitish, dotted yellowish-brown, thin and fragile, concave to straight across at the tip, and often extend above the leaf base. The ligule (membrane where the leaf joins the sheath) is longer than wide, pointed to blunt at the tip with loose tissue around the edge. Leaves are V-shaped in cross-section when young, and hairless though slightly rough along the edges. Old leaves persist to the next season before withering away.

Bases are wrapped in a light brown sheath that is not fibrous. Stems are 3-sided, smooth to rough along the angles, erect to ascending, elongating at maturity but usually shorter than the leaves. Not all plants produce flowering stems. Plants are clump-forming but not typically colony-forming. 

Fruit:

Fruit develops starting in late spring, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Pistillate spikes are densely packed with numerous fruits, the perigynia mostly ascending and overlapping like shingles.

Pistillate scales are elliptic, rounded at the tip, pale brown to dark red-brown or purple-brown with a broad green midvein, lacking awns, and narrower and shorter than the perigynia. Perigynia are green turning light brown at maturity, 1.7 to 3.2 mm long, 1 to 1.6 mm wide, weakly 5 to 7-veined on both surfaces, hairless, not much inflated but loosely wrapping the achene, lance-elliptic, widest at or below the middle, abruptly tapered to a stalk-like base, somewhat rounded at the tip or tapering to a minute, toothless beak. Achenes are 1.5 to 2 mm long, lens-shaped, reddish-brown at maturity.

Notes:

Carex lenticularis is an uncommon sedge confined to the arrowhead region of Minnesota, found along rocky or sandy shores, and in rock crevices on the north shore of Lake Superior.

Carex is a large genus, with over 600 species in North America and 150+ in Minnesota alone. They are grouped into sections, the species in each group having common traits. Carex lenticularis is in the Phacocystis section (a combination of former Acutae and Cryptocarpae sections); some of its common traits are: typically clump forming and rhizomatous, leaves V or M-shaped in cross-section when young and hairless except along the edges, spikes long and cylindric, spikes drooping to erect on slender stalks to nearly stalkless, terminal spike usually all staminate or with a few perigynia at the tip, perigynia densely packed, green to brownish, 2-ribbed, weakly veined and short-beaked, achenes lens-shaped with 2 stigmas, growing in wetlands and other wet places.

Carex lenticularis is among a group of 5 very similar species in Minnesota; the other 4 are Carex aquatilis, C. emoryi, C. haydenii and C. stricta. There are a few key characteristics that, in combination, help distinguish them from each other: clump-forming or not, the basal sheaths fibrous or not, the length of the lowest pistillate bract relative to the terminal spike, whether the perigynia is broadest above the middle or not. In some cases, the shape of the ligule, the length of the pistillate scales relative to the perigynia, or other characteristics are also relevant to a correct ID. Most references mention perigynia veins (or lack therof) as an important diagnostic, but we have found these to be pretty obscure in most cases, even under magnification, and sometimes the perigynia base is a bit pleated which might be mistaken for veins.

Of these five species, only C. aquatilis and C. emoryi are colony-forming and not clump-forming. Only C. aquatilis and C. lenticularis have the lowest pistillate bract consistently overtopping the terminal spike. Only C. haydenii and C. stricta have fibrous basal sheaths and form dense hummocks. Only C. aquatilis and C. haydenii should have perigynia widest above the middle, though any of these species may be widest at the middle, at least occasionally. C. aquatilis and C. haydenii have perigynia veinless on both surfaces but veins can be quite faint on the others. Inspect multiple specimens in a population to get a consensus on these traits, and mature specimens are always best though not always available.

C. lenticularis is the most distinct of these five, distinguished by the combination of: fruiting stems not more than 24 inches tall, clump-forming, not colony-forming, basal sheaths light brown and not fibrous, the lowest pistillate bract consistently over-topping the terminal spike, a single staminate spike but the terminal spike often has pistillate flowers at the tip (gynecandrous), pistillate spikes never have staminate flowers at the tip, perigynia widest at or below the middle and mostly tapered at the tip, and pistillate scales rounded at the tip and usually shorter than the perigynia. The other members of this group almost always have at least a few staminate flowers at the tip of upper pistillate spikes, never have pistillate flowers on the terminal spike, frequently have multiple staminate spikes, and all tend to form large stands.

There are 4 or 5 recognized varieties of C. lenticularis (depending on the reference), all but one of which are western species with only var. lenticularis found east of the Rocky Mountains. Of note is that, according to Flora of North America, var. lenticularis has pale brown to red-brown scales and the terminal spike is usually staminate. Of the plants we encountered in the field, the terminal spike is more often gynecandrous and pistillate scales are more often very dark purple-brown around the edge. Your mileage may vary.