Amelanchier arborea

Downy shadbush

Description
Trees or shrubs. Stems 1–10, 2–20 m, solitary or in small clumps, fastigiate,; twigs glabrous at flowering. Leaves conduplicate in bud; less than half-expanded and not unfolded, green or brownish, abaxially densely tomentose by flowering; petioles 10–25 mm; blades green abaxially, ovate to obovate, 4–10 x 2.2–5 cm, firm, bases cordate or rounded, margins serrate nearly to or to base with 6–10 teeth per cm, lateral veins 11–17 pairs, anastomosing and becoming indistinct near margins, apices acute to acuminate, surfaces and petioles sparsely pubescent or glabrous. Inflorescences 4–11-flowered, drooping, 3–5 cm, only proximalmost 1–2 pedicels subtended by leaf. Pedicels hairy, proximalmost 0.8–1.7 cm. Flowers: hypanthia campanulate, 2.5–3.5 mm diam.; sepals rapidly recurving after flowering , 2–3 mm, adaxially hairy; petals white or pinkish (in southern part of range), linear to oblong, 10–18 x 2–5 mm, not andropetalous; stamens 20; styles 5; ovary summit rounded, glabrous ( sparsely or densely hairy). Pomes maroon-purple, 6–10 mm diam., insipid. 2n = 34, 68.


Flowering/Fruiting
Flowering Mar–May; fruiting Jun–Jul.

Habitat
Dry to moist woods, mesic mixed hardwoods and pine-hardwoods, fields, thickets, roadsides; 0–10 00 m

Range
N.B., N.S., Ont., Que.; Ala., Ark., Conn., Del., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Tex., Vt., Va., Wis., W.Va.

Discussion
(see Systematics page for references cited)
Amelanchier arborea is distinctive for its relatively robust stems, approaching 40 cm in diameter. Its leaves, which are densely tomentose upon emerging from the overwintering buds, are not as well developed at flowering as those of most other Amelanchier. The usually glabrous ovary summit and relatively large, finely toothed leaves are also helpful in distinguishing it.

Amelanchier canadensis was applied by many early botanists to A. arborea and A. laevis until Fernald (1941) clarified the issue; this usage appears in some older manuals. S. McKay(in P. Landry 1975) transferred Amelanchier laevis to subspecific status under A. arborea, and these two taxa are generally considered to be closely related. Allozyme data show that, with one exception, populations of each species are more closely related to a nearby population of the other species than they are to conspecific populations (R. D. Overath and J. L. Hamrick 1998). The two taxa are readily distinguished in flower, however, when differences in leaf color, pubescence, and inflorescence size are evident. Amelanchier arborea has a more southerly distribution, and A. laevis extends much farther to the north.

Amelanchier arborea exhibits considerable intraspecific variation, and several subspecific taxa have been published in this species. A. arborea var. alabamensis differs in its densely hairy ovary summit. Variation in ovary-summit pubescence in A. arborea does not appear to be associated with any other taxonomically informative variation; individuals with varying amounts of ovary pubescence occur sporadically in populations but this does not appear ecologically significant. We conclude that this variety does not warrant taxonomic recognition. We have observed groups of populations that differ in the number of flowers per inflorescence, color of the expanding leaves, size of the teeth, and other features.

Amelanchier arborea generally flowers a little before A. laevis and to a week or more before congeners at the same site. Amelanchier arborea has been reported by M. L. Fernald (1950) to hybridize with A. bartramiana, A. canadensis, A. humilis, and A. laevis. We have collected putative hybrids with A. amabilis. Hybrid swarms have been reported in New Jersey between this species and A. laevis, but not with A. canadensis (J. E. Cruise 1964). Limited sampling suggests the possibility of fully or predominantly sexual individuals (C. S. Campbell and W. A. Wright 1996).