When most people envision a Black-eyed Susan, they are thinking of Rudbeckia hirta. This species is a short-lived perennial or biennial, often behaving as an annual. From a botanical perspective, it is characterized by its coarse, hairy stems and leaves (the species name "hirta" means hairy). The classic flower structure consists of a prominent, dark brown to black central cone (the "eye") surrounded by bright yellow, daisy-like ray florets. This species is the genetic foundation for many popular cultivars and is prized for its vigorous self-seeding habit, ensuring a persistent presence in the landscape. It thrives in full sun and well-drained soil, showcasing the typical resilience of the genus.
For gardeners seeking a more permanent fixture, Rudbeckia fulgida is an excellent choice. This species is a true, clump-forming perennial that spreads steadily by rhizomes to form dense colonies. Its foliage is generally less hairy than that of R. hirta, and the flower heads are slightly smaller but produced in incredible profusion from midsummer into fall. The most famous selection is Rudbeckia fulgida var. sullivantii 'Goldsturm', which has become a landscape staple for its exceptional flower power and ruggedness. This variety demonstrates the plant's evolutionary strategy of investing in a strong, spreading root system for long-term dominance in a sunny meadow or border.
When vertical accent is needed, Rudbeckia laciniata, or the Cutleaf Coneflower, stands out. This species is a robust perennial that can reach heights of 3 to 9 feet, supported by strong, branching stems. Botanically, it is distinct for its leaves, which are deeply lobed or divided, giving them a lacy, delicate appearance contrary to the plant's overall stoutness. The flowers also differ; the central cone is greenish-yellow and more elongated or cylindrical, while the ray florets droop gracefully. This adaptation likely attracts a different set of pollinators. It thrives in moist, fertile soils, often found naturally along stream banks, showing a greater tolerance for moisture than other species.
Rudbeckia subtomentosa, the Sweet Coneflower, offers a subtle but delightful botanical distinction. As the common name implies, the foliage of this perennial species has a slight vanilla or sweet fragrance, especially when crushed—a rare trait in the genus. The leaves are gray-green and less coarse, with a downy (tomentose) underside. The flowers are typical in shape but often have a greater number of ray florets, creating a fuller, more radiant appearance. It is a clump-forming plant that prefers consistent moisture but is still quite drought-tolerant once established, representing a balance between the ruggedness of the genus and a more refined aesthetic.
Plant breeding has expanded the palette of Black-eyed Susans far beyond the classic yellow and black. Hybrids, often involving crosses between R. hirta and other species, have introduced a stunning array of colors and forms. These include doubles and semi-doubles where the central cone is replaced with extra ray florets, changing the fundamental floral architecture. Cultivars like 'Cherokee Sunset' offer hues of bronze, mahogany, and gold, while the 'Prairie Sun' variety features a unique green central cone surrounded by lemon-yellow rays tipped in gold. From a plant perspective, these cultivars often sacrifice some seed viability and hardiness for their novel ornamental traits, making them more reliant on horticultural propagation.
