Circaea ×sterilis

Herbs glabrous or pubescent with at least a few hairs at nodes; stolons tipped by apical tuber or, more commonly, apex slightly dilated. Stems 7–70 cm. Leaves: petiole 0.8–5.5 cm; blade narrowly to broadly ovate, 2–7 (–11) × 1.3–4.2 (–7) cm, margins denticulate to prominently serrate, base cordate, apex short-acuminate to acute. Inflorescences 1.5–18 cm, sparsely to densely stipitate-glandular. Flowers opening after elongation of axis, ± loosely spaced; pedicels ascending to spreading at anthesis, 1.8–5.5 mm, with a minute, setaceous bracteole at base; floral-tube 0.4–1.2 mm, funnelform to narrowly so; nectary projecting beyond opening of floral-tube, 0.1–0.4 mm; sepals pink or pale green with apex commonly purple-tinged, narrowly oblong to oblong-obovate or ovate, 1.6–3.5 × 0.9–2 mm; petals white or pink, narrowly obtriangular to very broadly obovate, base cuneate to rounded, 1–3.6 × (0.6–) 1.5–3.6 mm; apical notch (1/3–) 1/2–3/4 length of petal; filaments 1.3–3.7 mm, pollen highly sterile (less than 2% fertile); style 2.7–4.7 mm. Capsules sterile, usually aborting before maturity, rarely developing to 3 × 1.5 mm, clavoid to obovoid, somewhat rounded to smooth or with low ribs and shallow grooves, tapering to pedicel, 2-locular, often with one locule larger, each with infertile seed. 2n = 22 (9 bivalents plus a ring or chain of 4, or 11 bivalents at meiosis).

Phenology: Flowering summer.
Habitat: Moist places in deciduous, mixed, or coniferous forests, especially in naturally disturbed areas along streams.
Elevation: 0–1000 m.

N.B., N.S., Ont., P.E.I., Que., Conn., Maine, Mass., Mich., Minn., N.H., N.J., N.Y., N.C., Ohio, Pa., S.Dak., Vt., Va., W.Va., Wis.

Discussion

Circaea ×sterilis is a sterile hybrid intermediate in morphology between C. alpina × C. canadensis. Although sexually sterile, like other hybrids in Circaea, it reproduces more vigorously vegetatively than either of the parents. Its occurrence in naturally disturbed places along streams no doubt results in portions of stolons being broken off and carried away during high water to establish new colonies some distance away; colonies often extend for great distances along streams. The hybrids persist many years and colonies discovered 100 or more years ago can still be found in the same locality, often in the absence of one or both parents. The hybrid also occurs outside the range of C. canadensis subsp. canadensis, most conspicuously on the Gaspé Peninsula, Quebec, and in northern New Brunswick, but also elsewhere. Those hybrids may indicate a once more northerly range for C. canadensis subsp. canadensis, or that seeds resulting from hybridization events can be transported outside the range of the parents by birds or mammals.

M. L. Fernald (1950) misapplied the name Circaea canadensis Hill to plants now known to be hybrids (C. ×sterilis) between C. canadensis and C. alpina in North America and placed C. intermedia Ehrhart, a name published later, in its synonymy. Circaea ×intermedia is the hybrid between the European C. lutetiana Linnaeus and C. alpina Linnaeus. Hill used the name C. canadensis for plants in North America, to distinguish them from the European C. lutetiana.

Selected References

None.

Lower Taxa