Know Your Natives – Prairie Ragwort

Prairie Ragwort (Packera plattensis, formerly Senecio plattensis) of the Aster, Sunflower, or Composite (Asteraceae) family is an herbaceous perennial with felty, white stem hairs and attractive, yellow, radiate flower heads. The genus name honors Canadian John G. Packer, author of Flora of Alberta. The epithet refers to the range from which the species was first described: “of the Platte River region.” Prairie Ragwort is widespread within central U.S. from north-central Louisiana and central Texas north to Indiana and eastern Montana. Widely scattered populations also occur in the eastern U.S. In Arkansas, it is reported from throughout much of the state but appears to be more common in the Ozark Plateaus and the Arkansas River Valley. Habitats include various dry to mesic sandy to limy soils in prairies, fields and open woodlands. The species is also known as Prairie Groundsel.

Prairie Ragwort has erect flowering stems to 2 feet tall which are unbranched, except within the inflorescence. Stems grow from short, vertically oriented, perennial rootstocks which extend deeper into the soil with age and become roughened by encircling leaf scars. One to several slender taproots may be present along with string-like fibrous roots, all growing from the rootstock’s tapered distal end. String-like, near-surface, white stolons (same appearance as the roots) extend off the rootstock and give rise to clonal plantlets. These may be as far as a half-dozen inches from the parent. Apparently, rootstocks survive for only several years, but, with continual production of new plantlets, the plant is perennial.

The rootstock may produce 1-3 closely spaced, light green to basally purple, hollow stems, clothed in woolly pubescence. As they age, stems may become more or less glabrous above, except for patches of woolly hair in the leaf axils.

Photo 1: This several-year plant with three growing stems has only string-like fibrous roots. The clonal off-set plant connects to the parent rootstock by a string-like stolon. Photo – April 24.

Plants have simple basal leaves. Early new leaves are oval to elliptic with later leaves becoming broadly lanceolate. Basal leaves, with long slender petioles, are dark green above and light green beneath. Early in the growing season, they have a dense mat of short appressed hairs (floccose pubescence). Oval leaves may be 6 inches long (including a 3½ inch petiole) and 1¼ inches wide, while lanceolate leaves may be 10 inches long (including a 5½ inch petiole) and 2 inches wide. Basal and stem leaves are shown in Photo 4. Leaves are firm to slightly leathery with the blade ascending along both sides of the midrib. Petioles are light green and grooved above, with the groove continuing along the leaf midvein. Basal leaves that grow later in the growing season are ascending to erect with the final leaves of the growing season being ground-hugging for surviving over winter months.

Photo 2: Early basal leaves of clonal plantlets are oval to elliptic with dentate margins and appressed floccose pubescence. Several additional plantlets can be seen. Photo – April 2.

Mid-stem to upper-stem leaves are sessile and alternate, measuring 6 inches long and 2 inches wide, but quickly reduced in size distally into the inflorescence. The blades are deeply, pinnately cut into a half dozen or more lobes, with midribs between lobes slightly winged. Larger basal lobes clasp the stem. Blades are mostly glabrous with sparse hairs beneath.

Photo 3: A plant at early stage of stem growth. It has oval to elliptic basal leaves and “transitional leaves,” lobed near the base, resembling soon-to-appear, mid- to upper stem leaves. Photo – February 20.
Photo 4: Display of basal to lower stem leaves (four on left) and mid- to upper stem leaves (four on right) with wing-like lobes and sessile/clasping bases. Upper and lower surfaces are shown alternately. Photo – May 2.

The inflorescence consists of “radiate” flowerheads––comprising both ray and disc flowers––arranged in corymbs that are further aggregated to form a compound corymb with all the heads at about the same height. As in virtually all composites, disk flowers of a head bloom centripetally––the outer, peripheral florets bloom first. In contrast, the central head of the corymb (as well as the central corymb of the compound corymb) initiates blooming––i.e., the heads bloom centrifugally. With each corymb having up to about 10 flowerheads, the entire cluster may have 40+ flowerheads. Flowering continues for about a month (April-May) before plants are overshadowed by later competitors, including prairie grasses.

Photo 5: This portion of a colony includes several plantlets and 20-inch-tall flowering stems. The clasping pinnate stem leaves decrease in size distally to the base of the inflorescence branches, transforming to tiny lanceolate bracts within the corymbs. Photo – April 4.

Flowerheads, to ¾ inch wide, are subtended by a rounded-elongate 1/4-inch-long involucre of a single series of 16± appressed, green, lanceolate, tomentose bracts (phyllaries). Heads comprise 80± central yellow disk florets and a dozen or so outer yellow ray florets. The perfect tubular disk florets (with pistil and stamens) have five short triangular flared corolla lobes. The pistillate ray florets (no stamens) bear ¼ inch long, strap-like ligules above their short tubes. Ovaries are surmounted by a pappus of erect hair-like bristles that later will aid in fruit dispersal. Disk florets have 5 stamens, the anthers of which form a ring around the developing style. As the style elongates through the anther ring, it plunges the pollen out of the anthers, transporting it to the surface of the head where it is available to pollinating insects. Thereafter, the style bifurcates and recurves to expose two elongate stigmas which capture pollen on their sticky surfaces from other florets.

Photo 6: As shown, peripheral disk florets of the central flowerhead are starting to open. Phyllaries, in a single series, remain edge-to-edge and appressed. Photo – March 31.
Photo 7: Stems, peduncles and involucres are pubescent, with the stem/peduncle junction having arachnoid pubescence. Bifurcated stigmas of flowerhead on right are covered with pollen. Photo – April 3.

Ovaries of fertilized florets quickly develop into single-seeded, non-dehiscing fruits (achenes). The elongate brown achenes, with ribbed sides, are about ⅛ inch long with a spreading “parachute” of many ascending straight white bristles (the pappus). Wind dispersal continues over a month or so.

Photo 8: As fruit matures, the base of the involucre enlarges. At maturity (on right) the bristle-topped achenes await dispersal by wind. Photo May 2.

For a shady or sunny garden, Prairie Ragwort has a nice height, interesting leaves, and showy flowers that reach peak bloom when many springtime flowers have faded. Plants provide nectar and pollen to visiting insects. On the other hand, with plants being stoloniferous, containment of a colony may become a challenge. Disposal of stems before seed dispersal would limit establishment of new colonies. It may be more appropriate for a prairie garden where it may be controlled by competitive grasses. The foliage is toxic to mammals (pyrrolizidine alkaloids).

Six additional species of ragwort are known to occur in Arkansas. Butterweed (Packera glabella) and Great Plains Ragwort (Packera tampicana) are annual species. Round Leaf Ragwort (Packera obovata) has glabrous stems and obovate basal leaves often with purple undersides. It usually is found in shaded, moister woods and can form large colonies. Golden Ragwort (Packera aurea) has glabrous stems and large heart-shaped basal leaves on long petioles. It grows in wetter areas, often associated with seeps, springs, or banks of spring-fed streams. Woolly Ragwort (Packera tomentosa) has tomentose pubescence covering leaves and the entire stems. Balsam Ragwort (Packera paupercula) may be the most similar species. This species is described as being highly variable both morphologically and ecologically and is still relatively little understood in Arkansas, so a comparison is difficult. It seems to have narrower, more elongate basal leaves and apparently flowers later than most of the other ragworts, including Prairie ragwort. More study of these species is needed.

Photo 9: Stem display of Round Leaf Ragwort (left), Prairie Ragwort (center), and Woolly Ragwort (right). Prairie Ragwort has pinnate cauline leaves with lobes extending to a narrow blunt apex.

Article and photographs by ANPS member Sid Vogelpohl

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