Amelanchier cusickii
Amelanchier nantucketensis
Cusick's serviceberry, Cusick's shadbush, saskatoon
Nantucket serviceberry, Nantucket shadbush
fully unfolded;
petiole (9–)12.8–19(–28) mm;
blade elliptic to suborbiculate, (22–)33–46(–61) × (13–)25–32(–50) mm, base subcordate to truncate, each margin with (0 or)1–6(–11) teeth on proximal 1/2 and (2–)4 or 5(–7) teeth in distalmost cm, largest teeth 1 mm, apex usually truncate, sometimes mucronate to acute, abaxial surface glabrous or sparsely hairy by flowering, glabrous (or sparsely hairy) later, adaxial glabrous later.
less than half-unfolded;
petiole (6–)9–15(–22) mm;
blade elliptic to oblanceolate or oblong-elliptic, (11–)29–41(–55) × (13–)19–29(–42) mm, base rounded to cuneate, each margin with 0–4(–10) teeth on proximal 1/2 and (0–)3–8(–12) teeth in distalmost cm, largest teeth less than 1 mm, apex subacute to rounded and mucronate, abaxial surface densely (moderately) hairy by flowering, surfaces sparsely hairy (or glabrous) later.
(4–)6–8(–10)-flowered, (17–)26–36(–47) mm.
(4–)6–8(–11)-flowered, (12–)24–36(–53) mm.
(0 or)1 or 2 subtended by a leaf, proximalmost (4–)9–14(–18) mm.
(0 or)1(or 2) subtended by a leaf, proximalmost (4–)7–14(–38) mm.
sepals erect to recurved after flowering, (2.6–)3.3–4.3(–5.3) mm;
petals obovate to oblanceolate, (10.8–)13.3–20.1(–23.2) × (2.3–)3.3–6.3(–7.5) mm;
stamens (14–)18–20(–21);
styles (4 or)5, (1.7–)2.6–4(–4.8) mm;
ovary apex glabrous or sparsely hairy (or with a ring of hairs at base of styles).
sepals irregularly spreading or recurved after flowering, (1.3–)2–3(–3.9) mm;
petals spatulate to oblong, (2.2–)3–4.5(–6.8) × (0.6–)1–2(–3) mm, sometimes bearing 1 or 2 tiny pollen sacs near margins on adaxial surfaces;
stamens (12–)18–20;
styles (4 or)5, (1.7–)2.6–3.7(–4.3) mm;
ovary apex glabrous or sparsely to densely hairy.
bluish black, 10 mm diam. 2n = 4x.
dark purple-blue, 7.5–10 mm diam. 2n = 4x.
Amelanchier cusickii
Amelanchier nantucketensis
Amelanchier cusickii has distinctively long petals. Leaves that are glabrous upon expanding and glabrous or sparsely hairy ovary apices are also useful for identification. The species flowers before A. alnifolia, which suggests that the two are genetically distinct. G. N. Jones (1946) noted that A. alnifolia and A. cusickii frequently grow together and that there is no evidence of hybridization; the authors have observed hybridization between A. alnifolia var. semiintegrifolia and A. cusickii.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
In the absence of flowering material, identification of Amelanchier nantucketensis is tentative; it is easily confused with A. spicata. K. M. Wiegand (1912) thought that A. nantucketensis originated as a hybrid between A. spicata (which he called A. stolonifera) and A. canadensis (as A. oblongifolia).
Amelanchier nantucketensis can reach 2.5 m but is usually much shorter, with spindly, straight, pale gray stems. Some petals of A. nantucketensis bear 1 or 2 tiny pollen sacs near margins on adaxial surfaces. Petal-borne pollen, which is highly unusual within the plant kingdom, is viable in A. nantucketensis and associated with a unique pollinator guild of native bees (A. C. Dibble et al. 1997). Conservation challenges for this apomictic tetraploid were discussed by Dibble and C. S. Campbell (1995).
Amelanchier nantucketensis has been documented to be self-compatible and able to produce seed asexually (C. S. Campbell et al. 1987).
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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