Spikes:

A cluster up to 2¾ inches long at the top of the stem, made up of 4 to 8 small spikes, those at the tip of the stem close to each other but not tightly crowded and the lower spikes all well separated from each other. All spikes are stalkless and have staminate (male) flowers at the tip and pistillate (female) flowers at the base (androgynous). At the base of each spike is a bristle-like bract, the lowest may be more leaf-like and often overtops the terminal spike.

Leaves and stems:

Leaves are basal and alternate along the lower quarter of the stem, the largest up to 16 inches long and 1.3 to 1.9 mm wide, mostly shorter than the flowering stems, initially erect becoming arching. Stem leaf sheaths tightly wrap the stem and are translucent whitish, concave and slightly thickened at the tip but easily torn. The ligule (membrane where the leaf joins the sheath) is as wide as or wider than long. Leaves are hairless, V-shaped in cross-section when young.

Old, dead leaves are often persistent to the next season. Bases are wrapped in a brown sheath that may become fibrous with age. Stems are erect to ascending to prostrate, very slender and only up to 1.5 mm diameter at the base, 3-sided, rough textured on the upper stem, elongating up to about 30 inches at maturity. Plants are densely clump-forming and not colony-forming. At maturity, the whole plant may flatten out in a radiating pattern.

Fruit:

Fruit develops in late spring through early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Pistillate spikes each contain 3 to 8 fruits that are spreading to reflexed (downward pointing). The remains of the slender styles tend to persist in fruit, though readily detach from the achenes; the 2 stigmas are often reflexed but straight to slightly twisted and 1 to 1.5 mm long.

Pistillate scales are egg-shaped, translucent white with a green midrib, blunt at the tip, awnless, and are up to half as long as the perigynia. Perigynia are 2.6 to 3.8 mm long, 1 to 1.5 mm wide, green to yellowish brown at maturity, hairless, thickened and spongy at the base, flattened on the back side, veinless except for several lines along the spongy base on the back side (best seen at maturity), generally lance-shaped in outline, widest at or below the middle, rounded to straight across at the base and gradually tapering at the tip to a short beak that has minute teeth along the edges and 2 small teeth at the tip. Achenes are 1.5 to 2 mm long, 1 to 1.4 mm wide, flattened lens-shaped, broadest above or below the middle, and mature to brown.

Notes:

Carex radiata is a common sedge found in moist to mesic deciduous or mixed woods, floodplain forests, pond edges, wetland margins, and only occasionally in more open areas. It is a great addition to a shade garden, developing large mounds and numerous flowering spikes, but robust plants tend to flatten out at maturity—an interesting phenomenon.

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 radiata is in the Phaestoglochin section; some of its common traits are: clump forming, basal sheaths usually fibrous, sheath fronts sometimes cross-wrinkled (rugose), leaves hairless and V-shaped in cross-section when young, 3 to 15 stalkless spikes (rarely the lower are branched), terminal spike with staminate flowers at the tip (androgynous), lateral spikes androgynous or all pistillate, perigynia ascending to spreading and flattened on the back side, rounded and spongy at the base, beaked, the beak usually toothed, flattened lens-shaped achenes.

Carex radiata is distinguished by the combination of: densely clump-forming, widest leaves less than 2 mm wide, up to 8 stalkless spikes with staminate flowers at the tip, spikes few-flowered and most widely separated, perigynia spreading to reflexed, 2.6 to 3.8 mm long, spongy at the base, veinless except for lines on the spongy base, styles often persisting in fruit, the stigmas usually reflexed but more or less straight and up to 1.5 mm long, and usually a woodland habitat.

Most similar is Carex rosea, which is overall more robust, has few persistent old leaves, widest leaves are at least 2 mm wide, perigynia are slightly larger (to 4+ mm long), and the stigmas are more tightly coiled, not straight. When styles are missing check the leaf width and the presence of numerous old, dead leaves for a determination. The arrangement of C. radiata perigynia is similar to some members of the Stellulatae section, which have staminate flowers at the base of a spike (gynecandrous) rather than the tip (androgynous).

Carex radiata and Carex rosea have a convoluted history. At one time we had C. rosea and C. convoluta, then C. rosea became C. radiata and C. convoluta became C. rosea (there should be a law against reusing names like that!). There is currently a mix-up of old Herbarium records for these two species and the distribution maps reflect that confusion. Someone will have to examine the old specimens and make new determinations before this is straightened out and the distribution within the state corrected.