Callianthe megapotamica comes from Brazil, where it grows as a medium-sized woody shrub with a natural arching habit that sends its branches cascading outward and downward in graceful sweeps. The flowers are the main event: small, pendulous, lantern-shaped blooms with butter-yellow petals extending below a bold red calyx, dangling from the branch tips in a display that persists from summer until the first frost. Hummingbirds discover these flowers reliably. Bees and butterflies do too. The leaves are elongated triangles with a heart-shaped base and serrated edges, medium green and clean against the profusion of color below. In frost-free zones 8 through 11, the shrub grows 5 to 8 feet tall and wide, becoming a substantial landscape presence. In cooler climates it performs equally well in a conservatory or as a large container plant moved indoors before the temperatures drop.

This is a fast-growing plant that benefits from deliberate pruning: cutting back by up to 40 percent in late winter or early spring maintains a compact, full shape and encourages the new growth on which flowers are produced. Spent blooms can be removed during the season to keep the display tidy, though the plant flowers so prolifically that deadheading is more aesthetic than necessary. Bright indirect light suits it best; direct midday sun can stress the foliage. Soil should be loamy, moist, and well-drained, and container plants benefit from repotting every one to two years as the root system expands. Stem cuttings taken during the growing season root readily. Watch for whiteflies, spider mites, and mealybugs, which find the lush growth attractive.