Know Your Natives – White-Nymph

White-nymph (Trepocarpus aethusae) of the Carrot (Apiaceae) family is the only species worldwide of the genus Trepocarpus––the genus is “monotypic.” Etymology of the generic name is uncertain. The specific epithet is a reference to Arethusa, a water nymph of Greek mythology. The species occurs in the central and southwestern portions of the Southeastern U.S., primarily from eastern Texas and Oklahoma to Alabama and Tennessee and north to southeastern Missouri, southern Illinois, and eastern Kentucky, with scattered occurrences in Georgia, Florida, and South Carolina. In Arkansas, it grows throughout most of the state except for portions of the Ozark Highlands. Habitats are moist to wet soils of lowland woods, floodplains, and swamp margins.

The herbaceous annual has a taproot to 2 inches long. First growth of a new plant appears during winter as a pair of long, grass-like cotyledons (seed leaves). The 2-3 foot tall mature plants bear alternate, highly dissected leaves on light green, finely ribbed, smooth and glabrous stems. Stem nodes are purple. Internodes zigzag from node to node. Crushed plant parts have a strong carrot odor.

Photo 1: Root and lower stem of a 2½ foot tall plant. The leaf on left subtends a branch while the leaf of branch on right has already dropped, as have lower leaves. Photo – July 6.
Photo 2: First growth in mid-winter is two grass-like, long cotyledons. Lobes of the lower compound leaves are wider than those that are more distal. Photo – March 2.

The compound leaves are triangular in outline, the leaflets and sub-leaflets dissected into delicate lobes. Lower and mid-plant leaves are 3-times pinnate and uppermost leaves are 2-times pinnate. Petioles, about ¼ inch long, have winged upper edges and clasping bases. A large, mid-stem leaf may be 3½ inches long (including petiole) and 4 inches wide. Mid-stem leaves have several to eight or more opposite pairs of leaflets. 



Photo 3: This young plant has straight internodes that zigzag from node to node. The long internodes and large dissected leaves give the plant an airy appearance. Plant at left is White Crown Beard. Photo – May 4.
Photo 4: Lobes gradually become acicular from the wider lobes of the stem leaf (on left) to leaves of branches (clockwise from upper right). Upper right leaf shows abaxial side; all others, show adaxial sides. Leaf at center, with a short floral stem, terminated a branch. Photo – July 6.

The inflorescence consists of compound umbels atop straight, leafless floral stems that are 2-4 inches long. Umbels consist of 3-4 umbellets that terminate straight ¼-½ inch long peduncles. Umbels and umbellets are subtended by several irregularly sized and positioned acicular bracts up to 1 inch long. Umbellets comprise 4-9 fertile and infertile flowers; pedicels of fertile flowers are very short (less than 1/16 inch) to absent while pedicels of the smaller infertile flowers may be ¼ inch long.

Photo 5: Umbels, on long leafless floral stems, consist of three to four umbellets. Umbels and umbellets are subtended by acicular bracts. Photo – June 27.

Fertile flowers, with spreading corollas slightly wider than 1/16 inch, have 5 minute acicular sepals, 5 petals, 5 stamens, and 1 pistil (consisting of an inferior ovary bearing 2 styles and stigmas). Floral parts are attached at the summit of a prominent naked ovary about ¼ inch long and 1/16 inch wide. 

Umbellets produce several to half a dozen or more elongate fruits. As fruits mature in mid-summer, the entire plant quickly fades. Fruits, remaining as paired nutlets, persist on the dead branches as the plant disintegrates. Seed dispersal may be birds dropping a nutlet while removing chaff or by water-transport of the buoyant nutlets.

Photo 6: The paired stigmas and styles can be seen emerging from a mounded structure called the stylopodium at the tip of the ovary on several flowers at right. The two carpels of the compound ovary are separated by a depressed area and can be seen on the flower at far left. Photo – May 26.
Photo 7: When dry, these fruits will split into two separate 1-seeded units called mericarps. Umbels are subtended by short acicular bracts; umbellets are subtended by longer acicular bracts. Flowers have short sepals that persist at fruit apex. Photo – July 18.

White-nymph, with lacy foliage and tiny white (nymph-like?) flowers, can be a lovely specimen plant, but can get lost among other plants. It can be an aggressive self-seeder and spreads easily in its preferred habitat. Spread can be controlled by removal of entire plants before seed dispersal. It may be suitable for a “controlled” area of a native plant garden or in a natural area. In midsummer, after seed-set, the plant quickly disintegrates. It is a host plant of the Black Swallowtail (Papilio polyxenes). It is not eaten by deer.

Photo 8: This plant in an open site shows the characteristic ascending and widely spreading branches. The plant is hosting several Black Swallowtail caterpillars. Photo – June 17.

Although white-nymph is the only species of its genus, its structure is somewhat similar to that of several other species in the carrot family in Arkansas. It can be recognized by its intricately dissected, flattened leaves and white-petaled flowers atop large, glabrous ovaries.

Article and photographs by ANPS member Sid Vogelpohl

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