Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Fls unisexual, without perianth, borne in spikes, each fl solitary in the axil of a scale; spikes unisexual or bisexual, when bisexual the staminate fls usually either termina(spikes androgynous) or basal (spikes gynaecandrous); stamens (2)3; pistillate fls individually enclosed by a sac-like scale (the perigynium), from the mouth of which the style or stigmas protrude, as well as being subtended by the open pistillate scale; stigmas 2 or 3, the achene accordingly lenticular or trigonous; grass-like perennial herbs with 3-ranked lvs, closed sheaths, and triangular or terete, mostly solid stems, the lower sheaths bladeless (plants aphyllopodic) or with ± well developed blade (plants phyllopodic); spikes solitary and terminal, or much more often racemosely arranged in a terminal infl that is rarely again branched, sometimes some of them well removed from the others and axillary to lvs near the base. 1500+, cosmop., especially in moist North Temperate and Arctic regions.
Some spp. of subg. Primocarex have a definite rachilla alongside the achene within the perigynium, showing that each pistillate fl represents a branch of an infl that has been reduced to a single fl. The perigynium is a highly modified bract on the adaxial side of this short, uniflorous branch. The bract wraps around the pistillate fl, and its margins are connate so that the fl is enclosed in a sac with a minute apical opening. In two of the four subgenera (Primocarex and Vignea) the line of fusion of the bract-margins can be seen as a suture or imperfection toward the tip of the dorsal side of perigynium. The side of the perigynium next to the pistillate scale is called the dorsal side, and the side next to the axis of the spike is called the ventral side. Many of the characteristically tristigmatic spp. of Carex occasionally have a few distigmatic fls intermingled; such specimens should be keyed as tristigmatic.