15a. Amelanchier canadensis (Linnaeus) Medikus var. canadensis
Amelanchier canadensis var. subintegra Fernald; A. oblongifolia (Torrey & A. Gray) M. Roemer
Shrubs, 0.5–8 m. Stems 1–25, in open to dense colonies. Leaves: blade oblong to oblong-elliptic or narrowly oblong-obovate, (24–)35–48(–67) × (12–)20–27(–42) mm, base rounded, apex subacute to rounded and mucronate, abaxial surface glabrous to moderately hairy, adaxial glabrous or sparsely (moderately) hairy. Inflorescences (3–)7–10(–15)-flowered, usually loose, (12–)21–37(–74) mm. Pedicels: 0 or 1(or 2) subtended by a leaf, proximalmost (6–)8–14(–17) mm. Flowers: sepals erect or spreading after flowering, (0.3–)2.1–3.1(–4.6) mm; petals linear to oblong, (4–)7–10.2(–15) × (1.8–)3–4(–5.3) mm; stamens (15–)19–20(–21); styles (3–)5. Pomes maroon-purple, 7–10 mm diam. 2n = 2x, 4x.
Flowering Mar–May; fruiting Jun–Jul. Damp soil of swamps, wet streamheads, bogs, moist to wet thickets, woods; 0–200 m; N.B., N.S., P.E.I., Que.; Conn., Del., D.C., Ga., Maine, Md., Mass., N.H., N.J., N.Y., N.C., Pa., R.I., S.C., Tenn., Vt., Va.
The dense colonies of larger plants, erect inflorescences, usually glabrous ovary apices, and sepals that are erect or ascending after flowering are, in combination, distinctive for var. canadensis. Unusual features are its restriction mostly to the Atlantic coastal plain and tolerance of hydric soils. The variety is abundant in forested wetlands and ecotones with fresh-tidal marshes in the Chesapeake Bay region. K. M. Wiegand (1912) and C. T. Frye (2006) noted that the inflorescence of var. canadensis does not elongate much following flowering.
Variety canadensis is remarkably plastic in habit, flowering at heights of less than 0.5 m in thin soils and growing to 8 m in better conditions. New Brunswick plus eastern Maine and Maryland plus Virginia have dwarf variants that do not appear to be edaphic. Fernald distinguished var. subintegra, which grows in low pine barrens of southeastern Virginia, by leaf blades that are entire or toothed only near the apex.
Variety canadensis is morphologically close to three species of eastern North America that have finely toothed leaves, glabrous ovary apices, and often grow into trees: Amelanchier arborea, A. intermedia, and A. laevis.
Variety canadensis generally flowers at about the same time as Amelanchier laevis. M. L. Fernald (1950) and J. E. Cruise (1964) reported that it hybridizes with A. arborea, A. intermedia, A. laevis, and A. spicata. Hybrids with A. arborea appear to be common and some microspecies may result. C. T. Frye (2006) reported morphologic evidence of introgression with A. obovalis. Tetraploid var. canadensis is self-compatible and produces seeds asexually (C. S. Campbell et al. 1987); diploids are self-incompatible and sexual (C. T. Frye, unpubl.).