Yellow meadow-parsnip or smooth meadow-parsnip (Thaspium trifoliatum var. aureum) of the Carrot (Apiaceae) family has small yellow flowers with in-turned petals, much like those of the golden-Alexanders (Zizia aptera and Zizia aurea) (see last paragraph). The genus name, coined by Thomas Nuttall, is a play on Thapsia, a related genus of the Mediterranean region. The specific epithet is Latin for “three-leaved.” In the U.S., Thaspium trifoliatum occurs primarily from Pennsylvania and Illinois south to Alabama and Arkansas.* Within Arkansas, it occurs statewide, most commonly in the Interior Highlands and on Crowley’s Ridge. Habitat includes clayey to sandy or rocky soils of sunny, moist prairies and partially shaded woodlands.
This herbaceous perennial, with erect stems to 2½ feet, is supported by a main root that becomes elongate and horizontally positioned near the soil surface. This root, to 2 or more inches long, bears numerous spreading to descending smooth, ropy, white roots that may be 8+ inches long. The main root becomes rough, irregular and knobby as old stems decay and “buds” of additional ropy roots form. A mature plant may have a single stem or multiple stems with each stem developing from a separate growth-point on the upper side of the main root.
Stems are not branched except for a few axillary floral branches just below the terminal inflorescence (see below). The round, slightly ridged, hollow, thin-walled, stems as well as all other parts of the plant, are hairless (glabrous).
Plants bear both basal (radical) and cauline (stem) leaves. Radical leaves are both simple and ternately compound, with 3 leaflets. Stem leaves are typically trifoliate. Margins are finely serrate, more sharply so distally, and highlighted by a thin but distinct white line which tends to be broader at the serration tips. Leaves are a medium to dark green, firm to rather leathery. Venation is well-expressed adaxially (above) and slightly recessed abaxially (below). Tertiary veins terminate at serrations’ tips. Leaves have sheath-like, clasping bases (see Photo 3).
Simple leaves are ovate with a cordate base and rounded apex. Leaflets of compound leaves become narrower higher on the stem, with more attenuate bases. Simple leaves occur on stemless seedlings and as radical leaves on mature plants. They have a combination of palmate and pinnate venation––the broader leaves with palmate venation, the more elongate leaves with mixed proximate palmate veins and distal pinnate veins. Simple leaves are 1-4 inches long, somewhat narrower in width, and with petioles 1-4 inches long.
Compound leaves are typically trifoliate, with a terminal leaflet and an opposite pair of lateral leaflets. Lateral leaflets are broadly lanceolate, often with asymmetric bases, 1-2 inches long and about 1 inch wide. Terminal leaflets are similar, but with bases symmetric. Size of the compound leaves varies from plant base to apex; larger leaves may be 11 inches long, including a 1 inch petiole, and 4 inches wide. Occasionally, terminal leaflets are subtended by an “extra” pair of lateral leaflets so that the odd-pinnate leaves have five leaflets.
Considerable variation occurs in length of petioles (leaf stalks) and petiolules (leaflet stalks). Leaves and leaflets may be stalked, subsessile or sessile. Uppermost compound leaves associated with the inflorescence tend to be sessile.
The inflorescence, from March to May, consists of compound terminal and axillary umbels (to 3 inches wide) on erect, straight peduncles to 3 inches long. Umbels branch into 6-10 grooved rays to ½ inch long, each ray terminating in an umbellet of 6-12 tiny, pedicellate flowers. All umbellets of a particular umbel bloom at the same time with flowers opening sequentially from perimeter to center.
The pale yellow flowers, less than ⅛ inch wide, have a short calyx of 5 tooth-like sepals, 5 broadly oval petals, 5 stamens, and a 2-celled inferior ovary topped with a stylopodium bearing a pair of styles. Ovaries have 10 longitudinal wings, widest at mid-ovary. Petals are strongly incurved toward the flower’s center and do not unfurl with age.
In mid to late summer, a fertilized flower produces a 3/16-inch-long broadly elliptical fruit with prominent longitudinal wings. When mature, fruits are hard and dry, and split into two 1-seeded mericarps, each with a semi-persistent style. Fruits may persist on dry stems into fall. Dispersal would be mainly by wildlife, strong winds, gravity and surface water flow.
Yellow meadow-parsnip is an attractive perennial that provides basal wintertime greenery and attractive leafy stems in early spring. Due to its tendency to self-seed, this species may be best suited for a natural area or wild garden. In a more formal setting, removal of fruits before maturity may be appropriate. Similar-appearing golden-Alexanders reportedly are not as aggressive in self-seeding.
Other Thaspium taxa in Arkansas are hairy meadow-parsnip (Thaspium chapmanii), hairy-joint meadow-parsnip (Thaspium barbinode), and purple meadow-parsnip (Thaspium trifoliatum var. trifoliatum). Purple meadow-parsnip differs from yellow meadow-parsnip primarily by its dark maroon flowers.** Hairy and hairy-joint meadow-parsnips (T. chapmanii and T. barbinode, respectively) have thinner, more divided leaves that are more prominently coarsely and irregularly sharply toothed. Hairy meadow-parsnip has pale yellow to creamy white flowers and hairier and more dissected (2-3-ternate) leaves, while hairy-joint meadow-parsnip has golden yellow flowers and less dissected leaves (1-2-ternate).
Two Arkansas species of Zizia are easily confused with yellow meadow parsnip: golden-Alexanders (Zizia aurea) and the less common heart-leaf golden-Alexanders (Zizia aptera). Golden-Alexanders (Z. aurea) has several characteristics to aid in its identification: 1) flowers are a darker yellow and the central flower of the secondary umbellet is sessile as opposed to pedicellate, 2) fruits are ribbed or without ribs rather than strongly winged, 3) basal leaves are all compound rather than simple, and 4) habitat preference is for more moist soils. Heart-leaf golden-Alexanders (Z. aptera) is quite similar to golden-Alexanders, except at least some basal leaves are simple and cordate.
* On national distribution maps, the two varieties are often not separated.
**Thaspium trifoliatum has been classified into two varieties. T. trifoliatum var. trifoliatum with maroon flowers and T. trifoliatum var. aureum with yellow flowers. T. trifoliatum var. flavum and Thaspium flavum are synonymous with T. trifoliatum var. aureum.
Article and photographs by ANPS member Sid Vogelpohl