Carex rostrata Stokes and Carex utriculata Boot are morphologically and ecologically similar wetland sedges (Cyperaceae). Both species can be found in suitable habitats throughout the Northern Hemisphere, but the former has an infrequent and localized distribution (Ball & Reznicek 2002). In North America the name C. rostrata has long been erroneously applied to plants that are actually C. utriculata. The true identity and distribution of C. rostrata in North American is still largely unknown. Indeed, only five of the hundreds of specimens labeled as C. rostrata at the UBC herbarium were actually C. rostrata. All remaining specimens were C. utriculata.
Because C. rostrata is rare (blue-listed) in British Columbia it is important to be able to distinguish it from the common C. utriculata. With a few tips this can easily be done in the field and herbarium. The foliage of C. rostrata has a whitish-green to grayish blue-green appearance, and C. utriculata tends to be pale-green to green. These species often co-occur with C. rostrata preferring the wetter parts of a wetland and C. utriculata preferring the drier parts (Fig. 1).
The whitish-green to grayish blue-green colour of C. rostrata seems to be caused by many tiny, tightly packed pimples (papillae) on the top (adaxial) side of the leaves. These papilla can only be seen with the aid of magnification strong enough (about 20-30X) to clearly see the tissue between the veins of the leaves (Fig. 2). The adaxial leaf surface of C. utriculata is usually smooth and green but may have some bumps (scabrous), however they do not affect the leaf morphology enough to alter the colour (Fig. 3).
In the absence of magnification these two species can still be discerned based on macro-morphological leaf characters. The leaves of C. rostrata are narrow (rarely up to 4.5 mm wide), broadly U-shaped in cross section; the margins are rolled up back toward the centre of the adaxial surface (involute); and the bottom (abaxial) side lacks a thin, short ridge running down its centre (Fig. 4). The leaves of C. utriculata are broad (>4.5 mm wise), broadly gull-winged to flat in cross section, do not have involute margins, and the abaxial surface has a thin short ridge running down its centre (Fig. 5). The Flora of North America has a very nice plate (Ball & Reznicek 2002, p. 505) that illustrates the leaf cross-section profile of C. utriculata and the papilla of C. rostrata very well. However, this plate does not show the involute margins of C. rostrata (Ball & Reznicek 2002, p. 505).
Table 1. Summary of key traits distinguishing Carex rostrata and C. utriculata
Ball, P., and A. Reznicek. 2002. Carex. In: Flora of North America North Editorial Committee, eds. 1993+.Flora of North America North of Mexico.12+ vols. Oxford Univ. Press, New York, USA. Vol. 23, pp. 255-572.
CANADA. British Columbia: A. Kruckeberg 364, July-16-1982, 1 km W of north tip, Texxeron L, and 5 km S of Kuzkwa R., on Leo Cr. Rd., UBC (54.79418 -124.739645, 2538 ft.); R. Annas s.n., August-5-1972, Ecological Reserve south of Parker Lake near Mile 308 of the Alaska Highway, UBC (58.812211 -122.898385, 1255 ft.); Beamish, Vrugtman, & Sperrings 8815, August-2-1961, Sphagnum bog, Selina Lake, Bowron. Rd., Wells area, UBC (53.2100 -121.4446, 3600f t.); Krajina & Pojar s.n., July-20-1974, Shores of Taltzen Lake, ca. 6 mi. WSW of Hwy. 16 along Kitsequecla road. Marshy shores of Taltzen Lake, UBC (54.931 -127.513, 2200 ft.).