Shrubs. Stems 1–70, 0.3–2.5 m, suckering and forming dense clumps. +/- stiffly erect, fastigiate; twigs glabrous at flowering. Leaves conduplicate in bud; less than half-expanded and -unfolded, green, abaxially densely tomentose by flowering;petioles 10–15 mm; blades abaxially green, elliptic to oblanceolate or oblong-elliptic, 1–1.8 x 1.1–3.5(–6.1) cm, thin, bases rounded to cuneate, margins serrate nearly or fully to base with 4–6(–10) teeth per cm or often entire proximal to middle, lateral veins (4–)6–7(–8) pairs, anastomosing and becoming indistinct near margins , apices subacute to rounded and mucronate, surfaces glabrous or with remnant of tomentum. Inflorescences 7–10-flowered, erect, 2.1–2.9 cm, only proximalmost 1–2 pedicels subtended by leaf. Pedicels glabrate, proximalmost 0.7–1.4 cm. Flowers: hypanthia campanulate, 4–5 mm diam.; sepals irregularly spreading or recurving after flowering , 1.9–2.4 mm, abaxially hairy; petals ivory, spatulate to oblong, 2.6–5.8 x 1–3 mm, sometimes andropetalous; stamens 20; styles 5; ovary summitsrounded, glabrous or densely lanuginose. Pomes dark purple-blue, 7.5–10 mm diam., sweet. 2n = 68.
Flowering Mar–May; fruiting Jun–Jul.
Fields, sandplain grasslands, heaths, glacial outwash plains, forest openings, disturbed sites, river shores, among rocks or sand, mostly dry habitats but also ditches, swales; 0– 300 m
N.S.; Conn., Maine, Md., Mass., N.H., N.J., N.Y., Va.
(see Systematics page for references cited)
In the absence of flowering material, identification of Amelanchier nantucketensis is tentative and it is easily confused with A. spicata. K. M. Wiegand (1912) thought that A. nantucketensis was of hybrid origin between A. spicata (which he called A. stolonifera) and A. canadensis (as A. oblongifolia). G. N. Jones (1946) lumped all andropetalous taxa into A. spicata. A. C. Dibble (1995) expanded the range for A. nantucketensis beyond eastern Massachusetts and considered A. oblongifolia var. micropetala (A. stolonifera forma. micropetala (Robinson) Rehder ) inseparable from A. nantucketensis, as both have andropetaly and do not differ otherwise.
Amelanchier nantucketensis can reach 2.5 m but is usually much lower, with spindly, straight, pale gray stems. Andropetaly is a highly unusual feature within the plant kingdom; it might not be present on every flower but can be found somewhere on the plant. The petal-borne pollen is viable and associated with a unique pollinator guild of native bees (A. C. Dibble and F. A. Drummond 1997). Conservation challenges for this apomictic tetraploid were discussed by A. C. Dibble and C. S. Campbell (1995).
Amelanchier nantucketensis has been documented to be self-compatible and to produce seed asexually (C. S. Campbell et al. 1987).