Know Your Natives – Cut-Leaf Coneflower

Cut-leaf coneflower (Rudbeckia laciniata var. lanciniata) of the Aster (Asteraceae) family occurs across the eastern U.S. to North Dakota and New Mexico.  In Arkansas, it occurs primarily in the Ouachita and Ozark Mountains.  The genus name established by Carl Linnaeus (developed binomial nomenclature in 18th century) commemorates his professor O.O. Rudbeck.  The specific epithet relates to the slashed or torn appearance of the leaves.  Other common names include tall coneflower, goldenglow and green-headed coneflower.

This herbaceous perennial, forming clonal colonies from its rhizomatous base, is native to flood plains and moist, fertile soils in partially sunny woodlands, thickets, sloughs and prairies margins.  It does well during hot and humid summers, but quickly wilts when soil becomes dry.  Colonies have stems that reach a typical height of 5 to 8 feet but may reach 10 feet.  Light green stems are terete (rounded), slightly ridged and are glaucous (with a waxy blue-gray sheen).  The tough, non-woody stems, about ¼-inch wide, have a pulpy white interior surrounding a hollow core.  Branching occurs near the top of the plant.  Overall, the plant is glabrous, but a few fine hairs may be found.

Leaves, dark green above and lighter green below, are mostly three-lobed, but with simple leaves high in the plant.  First leaves of spring can be shallowly lobed with serrated margins.  Later, alternate stem leaves are deeply three-lobed.  Stem leaves may be 12 to 16 inches long (including 2- to 6-inch petioles) and equally wide.  The three lobes of stem leaves are narrowly to broadly lanceolate with large serrations on margins.  Lobes may be dissected to the point that some lobes, especially terminal lobes, have secondary lobes.  Width of lobes reduces gradually toward their common junction so that they may be almost sessile at the rachis.  Lateral lobes are not symmetrical along their main vein–the side away from the midrib is wider.  Leaves approaching the inflorescence become smaller and unlobed, and petioles become shorter.  Margins of the smallest leaves are entire (not serrated).  Basal and lower stem leaves tend to drop in response to drying soil.

Petioles, with grooved upper surfaces and bases that wrap halfway around the stems, support ascending leaves with drooping tips.  Narrow wings of leaf blade may extend a short way down the petiole.

Venation is slightly incised above and strongly raised below.  Primary and secondary veins are mostly aligned along the long axis of leaves and leaf lobes, while secondary and tertiary veins are pinnate to net-like (reticulate).

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 1:  A young plant in late May showing relatively shallowly three-lobed leaves.

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 2:  An established colony in mid-April.  Three-lobed leaves are further deeply cut.

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 3:  Display of various leaf shapes and a stem segment.  Upper and lower surface of large stem leaves shown.

Inflorescence, in mid-summer, consists of solitary composite flower heads on long, naked peduncles at the ends of branching stems near the top of the plant.  In the area of the inflorescence, each stem leaf subtends one smaller axillary branch.  An axillary branch may itself produce one or more leaves from which, in like pattern, other axillary branches may continue this branching pattern.  At the final leaf of a branch or stem, a peduncle bears a single flower head.  With main stems diverging away from axillary branches, the main stems within the inflorescence zigzag from leaf to leaf.

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 4:  Uppermost flower heads of a 7-foot plant in mid-July. Of the pair of heads on right, one head (left) is at the apex of a main stem and the other (right) is an axillary head.

Within the inflorescence, a single stem may produce 40 or more composite flower heads.  Flower heads, very early in their growth, are exposed as green domes surrounded by 8 to 14 elongate, pointed, outward-flaring bracts (phyllaries) of unequal length and in several series.  With approaching anthesis, ligules of the 6 to 12 infertile ray florets, at first up-pointing flare outward, become bright yellow and broadly oblong-ovate with a pinched base.  Phyllaries and ligules, at anthesis, are somewhat droopy about the central disk that is ½ inch or more wide.  The diameter of the entire flower head is to 2 to 3 inches.  The central disk remains green until the 100+ disk florets open, at which time it becomes brownish yellow.  Yellowish tubular disk florets, about ¼ inch long and 1/32 inch wide, have a tubular corolla with 5 upward pointing, triangular lobes and 5 exserted stamens.  Split (bifurcated) stigmas become exserted later than the stamens.  The central disk, appearing prickly when in bloom, becomes brown as florets fade.  Fertilized disk florets produce 1/8 inch-long, 1-seeded, 4-sided, conical-shaped achenes with short bristles at the top edge.

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 5:  A pair of nectar-feeding wasps (Scolia bicincta) eat nectar and carry pollen from flower to flower.  Stamens (red arrow) and bifurcated styles (blue arrow) become exserted as florets become receptive to pollination.

Cutleaf coneflower - Rudbeckia laciniata var. lanciniataPhoto 6:  Display of leaves from upper branches, a branch segment and front and back of flower heads.  Note that central disk of small flower head on stem is already fully exposed.

In a garden setting, cutleaf coneflower is an eye-catching plant throughout the growing season.  Its extravagant leaves and interesting flowers place it on the “list of plants for consideration” for a partially shady, large garden or natural area.  However, the plant can become a vigorous colonizer.  Some of its many extending rhizomes and offset plants will probably need to be removed every year to maintain control.  In a too-sunny or too-dry site, leaves droop and the plant may wither.

Article and photographs by ANPS member Sid Vogelpohl

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