Not really a cranberry, but it has berries that can be a good substitute for cranberries. The leaves are much like the leaves of Red Maple (Acer rubrum), and the flowers come in dense cymes. Most of the flowers are tiny, but the outer flowers in each cyme, which are sterile, are immensely overgrown, making the whole cyme much more showy and a much more attractive target for pollinators. This bush was growing at the edge of the woods in Harmarville, where it was blooming in late May.
This species is often considered as variety americanum of the Eurasian species V. opulus, and so Gray classifies it:
VIBÚRNUM [Tourn.] L. ARROW-WOOD, LAURESTINUS. Calyx 5-toothed. Corolla spreading, deeply 5-lobed. Stamens 5. Stigmas 1-3. Fruit a 1-celled 1-seeded drupe, with soft pulp and a thin-crustaceous (flattened or tumid) stone. —Shrubs, with simple leaves, and white (rarely pink) flowers in flat compound cymes. Petioles sometimes bearing little appendages which are evidently stipules. Leaf-buds naked, or with a pair of scales. (The classical Latin name, of unknown meaning.)
§ 2. ÓPULUS [T onrn.] DC. Winter-buds scaly; leaves palmately veined and lobed; drupe bright red, acid, globose; stone very flat, orbicular, not sulcate.
V. Ópulus L., var. americànum (Mill.) Ait. (CRANBERRY-TREE, HIGH-BUSH CRANBERRY, PIMBINA.) Nearly smooth, upright, 1-4 m. high; leaves 3-5-ribbed, strongly 3-lobed, broadly wedge-shaped or truncate at base, the spreading lobes pointed, mostly toothed on the sides, entire in the sinuses; petioles bearing 2 glands at the apex; cyme broad, the marginal flowers neutral, with greatly enlarged flat corollas; stamens elongate. (V. americanum Mill.) — In woods and along streams, Nfd. and e. Que. to B. C, s. to N. J., Pa., Mich., Wisc., and n. e. Ia. June, July. (E. Asia.) — The acid fruit of this and the next is a substitute for cranberries. The well-known Snow-ball Tree, or Guelder Rose, is a cultivated state of the typical Old World form, with the whole cyme turned into showy sterile flowers.