Know Your Natives – Yellow Pimpernel

Yellow pimpernel (Taenidia integerrima) of the Parsley or Carrot (Apiaceae) family is an elegant and attractive herbaceous perennial with twice-compound leaves and compound umbels of tiny yellow flowers. The genus name comes from the Greek taenidion, “a small band,” referring to the scarcely prominent ribs of the fruit. The specific epithet, from Latin for “most entire,” refers to the smooth margins of the leaflets (unusual in the family). In the U.S., pimpernel occurs principally from Iowa and southeast Minnesota, south to eastern Oklahoma, and then east to New York and the Carolinas, excluding the Mississippi Embayment and most of the Atlantic and Gulf Coastal Plains. In Arkansas, it occurs within the Interior Highlands across the northwestern half of the state, along with two southeastern counties. Preferred habitat includes partially sunny to sunny, dry to moist, rocky to clayey soils of open woodlands and prairies. Taenidia is a small genus comprising only two North American species, of which only T. integerrima occurs in Arkansas. 

Mature plants have multiple stems to 3 feet tall which grow from a “crown” atop a carrot-like white taproot. The glabrous (hairless) and glaucous (whitish from a thin layer of wax) main stems typically have several lateral stems, often somewhat swollen at the nodes. In spring, plants are reddish, becoming greenish by the time of flowering, with the stems retaining a reddish hue. The root and other parts of the plant, when cut or crushed, have a pleasant celery scent.

Photo 1: Carrot-like taproots can become large. Stems grow from a “crown” atop the root.
Photo 2: First leaves appear in mid-winter. A stem will emerge from “within” the clasping petiole of the leaf at left. Photo – February 20.

Stems have several to a half-dozen widely spaced leaves that grow from rounded nodes. Along with the leaf, nodes bear lateral stems from leaf axils as well as floral stems directly from the node but opposite to the leaf base. Leaves are large, to 6-9 inches long and 6 inches broad, and 2 or 3 times compound. They are petiolate with clasping bases. 

Photo 3: Winter leaves remain close to the ground. Most leaflets have a simple ovate shape. As shown, venation is made prominent by reddish coloration. Photo – February 20.
Photo 4: New leaves grow from within clasping petioles of previous leaves. The striped segments shown in this photo are clasping bases of new leaves which contain hidden rudimentary additional leaves, stems and inflorescences. The yellow mass is a compound umbel just beginning to expand. Photo-March 15.

Ultimate leaflets, to 1¾ inches long and 1 inch wide, are oval to elliptic and often lobed. Leaflet margins are smooth; tips are narrowed to a blunt or sharp point. Leaves are glabrous.

Photo 5: Display of lower, middle and upper twice-compound leaves. Upper surfaces shown on left and lower surfaces shown on right. 
Photo 6: Plants are erect, with terminal inflorescences. This elegant plant is 26 inches tall. Photo – April 27.

Glabrous inflorescences comprise open, loose, compound umbels (3 to 6 inches wide) terminating the floral stems. Floral stems bear 8 to 18 rays (to 3 inches long) which, in turn, bear the secondary umbels or umbellets. All flowers of a compound umbel bloom at the same time. With several umbels at the upper portion of stems, a plant is in flower for a month or more. 

Photo 7: This compound umbel, 2¼ inches across, has 17 umbellets that are about ¼ inch across. Stalks of the umbellets are typically called rays.

The bright yellow flowers, less than 1/16 inch across, have five broadly oval inturned petals and five stamens. Sepals are absent. Flowers at the perimeter of umbellets are perfect (with stamens and pistils) while interior flowers are staminate (stamens only). Stamens, with knobby anthers, extend between and well above petals. Ovaries are inferior, each topped with a tiny pair of styles. Pedicels of fertilized perfect flowers continue to grow as fruits mature and staminate flowers fade away. A fertilized flower produces a 3/16 inch long fruit that separates into two halves, each with five longitudinal ribs.

Photo 8: Flowers at perimeter of umbellets are perfect while interior flowers are staminate. Note developing fruits.

In a garden setting, the leafy yellow pimpernel would be an attractive plant with reddish foliage and bright yellow compound umbels. However, it readily self-seeds and can re-grow from decapitated taproots. Also, fruiting umbels are not positioned for quick removal. The plant would be suitable for a partially shady, fertile natural area. It provides pollen and nectar to a wide variety of small insects and is host plant for the Black Swallowtail (Papilio polyxenes ssp. asterius) and Ozark Swallowtail (Papilio joanae).

Article and photographs by ANPS member Sid Vogelpohl

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