Hypericum canadense
Perennial or annual herb, perennating by autumn basal offshoots, 0.3-0.6(0.75) m tall, erect, with stems few or solitary, often with strict or ascending branches from upper nodes, not rooting, with taproot. Stems green, 4-angled, scarcely ancipitous above, with lines smooth, internodes 2 mm (lower) to 30 mm (upper) long, shorter than to exceeding leaves,. Leaves sessile to subsessile, erect or spreading, not tetrastichous, persistent; lamina (6-) 10-40 (-55) x 0.5-4(-5.5) mm, linear to oblanceolate-linear (the lower oblanceolate to obovate), plane, not cucullate, midrib prominent proximally, smooth, slightly paler beneath, not glaucous, chartaceous; apex rounded, margin entire, base parallel-sided to attenuate, not sheathing, free; basal or near-basal veins l-3(-5), without or with 1-4 pairs of ascending midrib branches, tertiary reticula-tion obscure, dense; laminar glands dense, punctiform, not prominent. Inflorescence 1-c. 35-flowered, terminal, branching regularly dichasial or monochasial above 2nd or 3rd node, sometimes with ascending pairs of flowering branches from up to 8 nodes below, the whole diffusely corymbiform to cylindric; pedicels 1-3 mm long; uppermost leaves and bracts subulate, entire. Flowers 5-6 mm in diam., stellate. Sepals 2.5-4.5 x 0.8-1 mm, linear-lanceolate to lanceolate or rarely ovate, acute to acuminate, margin entire; veins 3-5, unbranched, not prominent. Petals golden yellow, occasionally veined red outside, 2.5-4 x 1-l.4(-2) mm, equalling or shorter than sepals, elliptic to narrowly obovate; apiculus and glands absent. Stamens 12-25, obscurely 3-5-fascicled, longest 2-2.5 mm long, c. 0.7 x petals. Ovary c. 2 x 1 mm, ovoid-conic; styles 3, 0.5-0.8 mm long, c. 0.3 x ovary; stigmas narrowly capitate. Capsule 4-6 x (l.5)2-2.5(-3) mm, narrowly conic to conic-cylindric, exceeding sepals. Seeds 0.5-0.7 mm long; testa finely linear-scalariform.
2n = 16 (Moore, 1973; Kapoor, 1982); n = 8 (Hoar & Haertl, 1932; D. H. Webb, 1980).
Bogs, marshes, depressions, lakes and pond margins; lowland.
Canada (eastern Ontario to Newfoundland). St. Pierre & Miquelon. U.S.A. (Minnesota to Maine, south to Florida and west to Alabama and Mississippi).
H. canadense was the (derivative) eastern member of a vicariant species pair, of which H. majus was the western member; but the pair became sympatric in glaciated north- eastern North America by the subsequent migration eastward of H. majus, and they now hybridise freely (see Utech & Iltis (1970), Webb (1980), and below). H. canadense may also have helped this intermixing by migrating westward; according to Utech & Iltis it appears to have spread in Wisconsin since 1930. It differs from H. majus by the narrower, linear (not lanceolate) leaves and smaller flowers and fruits.
H. canadense was first collected in Ireland in 1906 (Webb, 1969), but the specimen was not correctly identified until after the second collection, in 1954, from Lough Mask, Co. Galway (Webb, 1957). It is currently known from five distinct localities near Lough Mask in Co. Galway and Co. Mayo, as well as from one locality in the south of Ireland (Co. Cork, Glengarriff). The provision of open habitats by grazing and trampling of wet turf by cattle seems to be an important factor in its distribution in Ireland. It is likewise termed a pioneer by Utech & Iltis (1970).
The first record of H. canadense from eastern Holland (Almelo, Prov. Overijsel) was in 1909 (Jonker, 1959; Heine, 1962). It was subsequently refound in 1918 but not recognised until Jonker collected it in the same area (at Harbrinhoek) in 1934 (Jonker, 1935). In Holland it grows in dune slacks. The status of H. canadense in Europe has been much debated, and Webb (1958) and Webb & Halliday (1973) have reviewed the evidence. Its occupation of natural habitats remote from habitation and human activity, and the absence of a noticeable increase in area since its discovery, suggested that it is an established member of the Irish and Dutch floras, possibly a periglacial survivor. On the other hand, its relatively recent discovery in areas that were well-known to some earlier botanists, as well as the discovery in scattered European localities, at various dates since 1834, of four other closely related North American species (Heine, 1962; Robson, 1968), tends to indicate a more recent arrival. Introduction by human agency seems unlikely (except perhaps to Glengarriff (Lousley, 1971)), but long-distance transport (ancient or recent) by waterfowl remains a distinct possibility. [Subsequent work has produced strong evidence that it has almost certainly been introduced to Ireland and probably from there to Ireland by birds. See Part 9.] Bouchard (1954), however, thought that the French population of H. majus (Haute-Saône) could have been introduced with fodder for American horses during the 1914-1918 war.
As well as crossing with H. majus, H. canadense hybridises with H. mutilum and H. boreale and possibly H. gymnanthum.
Britton (1891) and D. H. Webb (1980) both doubted that the type of H. canadense [var.] β minimum Choisy belonged to H. canadense, but I can confirm that it does do so.