Circaea ×sterilis
Onagraceae tribe Circaeeae
7–70 cm.
petiole 0.8–5.5 cm;
blade narrowly to broadly ovate, 2–7(–11) × 1.3–4.2(–7) cm, margins denticulate to prom-inently serrate, base cordate, apex short-acuminate to acute.
opposite or whorled, [alternate];
stipules present.
1.5–18 cm, sparsely to densely stipitate glandular.
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.
primarily protogynous, actinomorphic and 4-merous, or zygomorphic and 2-merous;
stamens 2 times as many, or as many, as sepals;
pollen shed in monads.
indehiscent, either a fleshy berry or a dry capsule, covered with stiff, hooked hairs.
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.
1–500, without hairs or wings.
= 22 (9 bivalents plus a ring or chain of 4, or 11 bivalents at meiosis).
Circaea ×sterilis
Onagraceae tribe Circaeeae
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.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
Genera 2, species 117 (2 genera, 4 species, including 1 hybrid, in the flora).
All previous classification systems have placed Circaea and Fuchsia into different tribes, based on their morphological and geographical differences. Molecular analyses place these genera into a single clade (C. J. Bult and E. A. Zimmer 1993; E. Conti et al. 1993; R. A. Levin et al. 2003, 2004; V. S. Ford and L. D. Gottlieb 2007) that is as or more strongly supported than are other clades. The two genera share the feature of indehiscent fruits, expressed in Fuchsia as fleshy berries and in Circaea as dry fruits covered with hooklike hairs; nonhomologous indehiscent fruits also occur in Onagreae. The only occurrences of protogyny in the family occur in these two genera (not in all species of either, P. H. Raven 1979).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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