Echinacea (purple Coneflower) Plant Morphology

The Echinacea plant has fascinating anatomy. What appears to be a single flower head is actually hundreds of tiny flowers on a single structure. This article describes the intricate morphology of this plant.

Habit

Echinacea are deciduous herbaceous perennials. All have a taproot except for Echinacea purpurea. They have a short crown from which emerge 5 to 7 erect stems that are arranged alternately. The plant forms a slowly expanding clump that may be divided every few years. The wild-type Echinacea are typically 2 wide and 3-4 tall. However, the high-plain taxa from Texas north to Canada tend to be smaller than the eastern taxa. Modern hybrids have been selected for a smaller stature and range from 10 to 3 tall by 2 wide. In the wild, a single plant can live up to 40 years. The garden forms look their best if they are divided every 4 years.

Leaves

Echinacea leaves vary and may be linear, lanceolate, elliptic or ovate in shape depending on species and on the placement of the leaf. Lower leaves are larger and more rounded at the base, but upper leaves are smaller and thinner with a heart-shaped base. Lower leaves often have their own stalks (petioles) but the upper leaves are usually directly attached to the stem. The leaf margins are usually smooth (entire) but may have some dentation or serration. Most species have very rough textured leaves with varying amounts of hairiness (hirsutism).

Flower

Like all plants in the Asteraceae family, Echinacea flowers are actually inflorescences; a collection of many small fertile florets bunched together on the cone in the center of the inflorescence. The petals of Asteraceae flowers are also florets, just sterile ones. Inflorescences in the Asteraceae family have a special name, a capitulum. A capitulum consists of a flattened receptacle with the central portion containing 200-300 small fertile florets encircled on the outer edge by a single rank of one or two dozen sterile florets. These are called disk florets and ray florets respectively. The purpose of the ray florets (also called ligules) is to attract pollinators with their bright colors, while the disk florets are where pollination occurs. Each disk floret is 5-lobed and situated among sharply-pointed, stiff bracts called palea. The overall appearance of the inflorescence is that of a single flower with many anthers and stigma in the middle. The ray florets are soft, colorful and petal-like. The inflorescence usually has a dozen or more small green bracts (phyllaries) beneath it on a structure called an involucre.

If you look at a coneflower very carefully, you will note that the disk florets do not all shed pollen (reach anthesis) at the same time. The center disk florets open first, and proceed in an outward succession over the course of several days. You can watch this procession and use it to estimate how much longer your flower is going to live.

The inflorescence is held on a strong, rigid, hirsute, unbranched stem (peduncle) that grows to 36 tall or more. There may be small leaves spaced widely along the length of the flower stem. There will be many inflorescences produced in an overlapping sequence starting in July and continuing until frost. The overall effect is that there are up to a dozen inflorescences open simultaneously. Purple coneflowers are ideal for cut flower gardens because of the large flowers on long, sturdy stems. The inflorescences remain open and colorful until they are pollinated. At that time, the color fades to gray and the inflorescence dries up without falling off. Modern hybrids often have reduced fertility or outright sterility which means that their flowers often remain colorful longer than the wild types.

The disk florets may be dark burgundy, black, white, yellow or orange. The traditional color of Echinacea ray florets is pinkish-purple or sometimes yellow or white. However, modern hybrids have broken through this color barrier and may be shades of orange, peach, salmon, and reddish-orange. In wild-type Echinacea, the ligules may be held outward but are usually reflexed downward to varying degrees. The ligules may be wide and overlap each other, but are more commonly narrow with space in between them. Modern breeders have selected strongly for ligule architecture and the hybrids tend to have wide, overlapping, ray florets that are held outward. The wild-type Echinacea purpurea are very lightly scented but Echinacea simulata and some of the modern hybrids are very sweetly scented. The entire inflorescence may be from 2 to 7 wide.

Fruit and Seed

The dry, angled, shark-tooth-shaped fruit of Echinacea is called a cypselae or an achene. It is tan, brown, or bicolored. Each inflorescence can produce as many as 100 seeds. Healthy plants produce several dozen flowers per year, so seed production is prodigious.

We hope you have enjoyed this tour of the Echinacea plant anatomy.