Know Your Natives – Rue-Anemone

Rue-Anemone (Thalictrum thalictroides; formerly Anemonella thalictroides) of the Buttercup (Ranunculaceae) family is a small, perennial, woodland ephemeral with an umbellate inflorescence of white to pink flowers. The genus name is the Latin form of the Greek word thaliktron, used in ancient times to describe some meadow-rues, possibly in reference to their compound leaves. The specific epithet, originally applied when the species was treated in the genus Anemonella, is a reference to the similarity of its compound leaves to those of the meadow-rues, plants already treated as species of Thalictrum. In the U.S., Rue-Anemone occurs from northeast Texas and southern Arkansas to Minnesota and east to the Atlantic Coast, reaching the Gulf Coast in Mississippi, Alabama, and the panhandle of Florida. In Arkansas, Rue-Anemone occurs across much of the state except for some portions of the Mississippi Alluvial Plain and low-lying areas of the West Gulf Coastal Plain. The common name “Rue-Anemone” is based on this species’ leaves being similar to those of the meadow-rues and its flowers being similar to those of the anemones. Other common names include Windflower based on the flowers’ quick response to breezes. Rue-Anemone is found in well drained, sandy to loamy, mesic soils within open deciduous woodlands and thickets and along woodland margins.

Rue-Anemone, an herbaceous perennial, occurs as isolated plants. The rootstock consists of a single tuber or 2-3 tubers joined at their tips. Depending on the time of the year, tubers may be globose or spindle shaped (fusiform). During the growing season, tubers shrink. When tubers become dormant in early summer, with nutrient reserves replenished, they are white and globose (see Photo 7). Whether a plant has one or several tubers, leaves and stems grow from a single near-surface caudex. Tubers are to 1½ inches long with long fibrous roots. Mature plants have one to several compound basal leaves and one to several floral stems. Stems and leaves grow directly from the caudex. The entire plant is glabrous (without hairs). Plants go dormant with the heat and dryness of summer.

Photo 1: Plants may have single or 2-3 fusiform to globose tubers. As shown, tubers on left have shriveled due to late winter vegetative growth. Lower portion of leaves and stems of plant on right are white and twisted due to an overcover of fallen leaves. Photo – March 22.

Floral stems appear in late winter before the basal leaves. When stems first appear, flowers are hidden by a protective layer of leaf-like bracts. At full development, stems are 4-9 inches tall––an erect wiry leafless peduncle (or scape) topped with the inflorescence, surrounded by an involucral whorl of 3-9 bracts. The bracts, unlike the leaves, are simple, with a single rounded to obovate blade (see below) on a long wiry thread-like petiole. The inflorescence consists of a single flower (occasionally) or an umbel of 3-6 flowers (usually 3) on ascending thread-like pedicels to 1½ inches long. Umbels have a central larger flower which blooms before the laterals. Infrequently, a flower may have an “extra” subtending bract. Peduncles and pedicels are reddish in sunnier habitats, but trending to light green in more shaded habitats. Peduncles are typically three or more times longer than the pedicels.

Photo 2: Involucral bracts form a protective layer for emerging flowers. Basal leaves emerge after the floral stems. Photo – March 9.

Basal leaves are biternate (twice ternate) with three compound leaflets on a straight wiry petiole. Each compound leaflet has a terminal subleaflet and an opposite pair of lateral subleaflets. While leaves may be 3-10 inches long, a typical leaf is 3½ inches long and 2½ inches wide, including a 2-inch petiole, 1-inch petiolules (leaflet stalks), and ¼-inch subleaflet stalks. The glabrous leaves and bracts, all about the same size, are rounded to obovate, with rounded, indented base and a broad apex with 3 rounded shallow lobes. Blades, to about ¾ inch wide and broad, quake in the breeze. Venation is ternate, with primary veins terminating at the three main lobes. The upper leaf surface is medium green, the lower light green to purplish, especially along the veins. Blades of terminal leaflets and involucral bracts are similar in size and appearance.

Flowering may extend over the month of March and into April. Umbels, with 3-6 perfect (with stamens and pistils) flowers, have a central flower which blooms first and tends to be the largest flower of the umbel. Flowers, to 1 inch across (occasionally 1½ inches), have a showy calyx of 5-10 large petal-like sepals (true petals are absent), which may be pure white to pinkish (varying by plant), the pinkish flowers being an even darker pink in bud. Sepals are oblong to broadly lanceolate (with or without a tiny notch at the apex) and may be in a single or double layer. Flowers have numerous stamens with delicate, long, white filaments topped with bright yellow, 2-lobed anthers. Stamens surround up to 15 closely packed, postlike, stubby pistils, the green ovaries topped by short white styles and stigmas. Anthers are positioned above the stigmas, flowers above their leafy involucral bracts.

Photo 3: Flowers arise on thread-like pedicels above the leaf-like single-blade involucral bracts. The numerous stamens have anthers which are positioned above the stubby closely packed pistils. This plant has pure white sepals in a single layer. Photo – March 20.
Photo 4: This plant has pink sepals in a double layer. This central flower (1 inch wide) is surrounded by four additional flowers (partially shown) to form an umbel. Two flowers are subtended by “extra” bracts (lower left and upper right). Photo – March 22.
Photo 5: An unusual plant with large flowers (1 5/8 inches across) with broadly lanceolate sepals. Photo – March 22.

Fertilized ovaries produce ribbed seeds with a fusiform shape less than ¼ inch long, with a slightly skewed apex. A flower may bear up to 15 1-seeded fruits (achenes) which stand erect on a small spheroid base. Seeds, with 8-10 prominent longitudinal ribs, do not dehisce (split) when dry. At the end of the growing season (with hot or dry weather), with plants becoming dormant, tubers are white and globose.

Photo 6:  Seeds with a fusiform shape with about ten rounded ribs extended from base to apex.  As shown, remnants of the stigmas are persistent.  Photo – April 9.
Photo 7: By the end of the growing season, the tubers have become globose with the storage of nutrients. Photo May 27.

For a garden or natural area, Rue-Anemone would be an excellent choice for a partially shaded flower bed or an open deciduous woodland. Although of small stature, flowers and leaves are decorative and interesting. Plants reliably produce blooms in late winter/early spring which provide pollen (no nectar) to early-season small bees and other insects. Flowering may persist for a month, the flowers remaining open during darkness and rainy periods. Rue-Anemone does self-seed well in favorable habitats, so that it is a good choice for a naturalized landscape. It is not eaten by deer.

Four additional species of the genus Thalictrum occur in Arkansas: Arkansas Meadow-Rue (T. arkansanum), Purple Meadow-Rue (T. dasycarpum), Early Meadow-Rue (T. dioicum), and Wax-Leaf Meadow-Rue (T. revolutum). Rue-Anemone may be distinguished from these four species by its small size, conspicuous petaloid sepals, leaf-like involucral bracts, ascending stamens, and umbellate inflorescences.

The Arkansas species most likely to be confused with Rue-Anemone is False Rue-Anemone (Enemion biternatum) which has similar size, leaves, and flower characters. However, False Rue-Anemone has several key differences: 1) Single flowers are axillary, 2) Flowers are always white and typically have five sepals, 3) Lobes of blade are incised, and 4) Fruits are dehiscent follicles rather than indehiscent achenes.

Photo 8: False Rue-Anemone is similar to Rue-Anemone but has single axillary flowers, white sepals only (none pink), incised leaflet blades, and follicle fruits. Photo March 21. (Photo courtesy of Eric Hunt)

Article and photographs by ANPS member Sid Vogelpohl

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