Loosestrife family (Lythraceae)
Description: This native plant is a summer annual that often branches at the base, otherwise it is usually unbranched. The erect or sprawling stems are about ½–1' long. They are light green, glabrous, and either round or angular in circumference. Pairs of opposite leaves occur at intervals along these stems. They are up to 2½" long, ¼" across, linear or linear-lanceolate, smooth along the margins, and glabrous. Each leaf clasps the stem at the base, where it often has a pair of small shallow lobes (i.e., it is auriculate). Along the upper surface of each leaf, there is a conspicuous central vein that runs along its length. From 1-7 flowers are produced in tight clusters in the upper axil of each leaf. These flowers are sessile, or nearly so. Usually, fewer flowers are produced per axil in the upper leaves (about 1-3) than in the lower leaves (about 3-7). Each flower is about ¼" across, consisting of 4 rounded petals that are pink or purple, a tubular calyx that is divided into 4 segments that form ridges at their edges, 4 or 8 stamens with yellow anthers, and a stout central style. The calyx is initially green or purple, but it later becomes red when the seeds begin to ripen. In the middle of each calyx segment, there is a secondary ridge along its length; these 4 secondary ridges are slightly less pronounced than the 4 primary ridges between the segments of the calyx. The blooming period occurs from mid-summer to early fall and lasts about 2-3 months. Individual flowers are short-lived. An ovoid seed capsule develops within the surrounding calyx that causes it to swell in diameter. This capsule contains numerous tiny seeds that are shiny and yellow. These seeds are small enough to be blown about by the wind, and they probably float on water. The root system consists of a shallow tuft of roots. This plant spreads by reseeding itself.
Cultivation: The preference is full sun, wet conditions, and muddy soil. The seeds germinate better if they are temporarily submerged in water, and then left in muddy soil. This emulates their natural habitat.
Range & Habitat: Scarlet Toothcup is an occasional to locally common plant in most areas of Illinois, except in the upper two tiers of counties, where it is largely absent (see Distribution Map). Habitats include muddy shores of ponds, mud flats along rivers, ditches, limestone quarries, and grassy areas that are prone to occasional flooding. This species tolerates disturbs conditions in wetlands.
Faunal Associations: The nectar of the flowers attracts various insects, including small bees (Little Carpenter, Halictid), Syrphid flies, Tachinid flies, and small- to medium-sized butterflies (Whites, Sulfurs, & others). The bees also collect pollen. The seed capsules are eaten by ducks during the fall and winter, including Anas platyrhynchos (Mallard), Anas acuta (Northern Pintail), and Anas crecca (Green-Winged Teal). The foliage is not known to be toxic, and it is probably eaten by Branta canadensis (Canada Goose).
Photographic Location: Along the muddy shore of a pond in Champaign, Illinois.
Comments: The common name, 'Scarlet Toothcup,' refers to the appearance of the fruits when they begin to ripen during the fall. Another common name for this species is 'Purple Ammannia,' which refers to the color of the flowers. Scarlet Toothcup is a wetland species that is not very showy and often overlooked, although it is useful as a source of food for waterfowl. The only other species in this genus that occurs in Illinois, Ammannia robusta (Robust Toothcup), was formerly regarded as a subspecies of Scarlet Toothcup, or Ammannia coccinea robusta. However, genetic analysis has revealed that it is a distinct species. Robust Toothcup occurs primarily in NE Illinois and has an appearance that is similar to Scarlet Toothcup. The petals of its flowers are light pink to pink and there are only 1-3 flowers (or seed capsules) per leaf axil, whereas Scarlet Toothcup has flower petals that range from pink to purple and there are often 3-5 flowers (or seed capsules) per axil among the lower leaves (and sometimes even more). Another wetland species in the Loosestrife family with a similar appearance is Rotala ramosior (Wheelwort). Unlike the preceding Toothcup species, Wheelwort has only a single flower or seed capsule per leaf axil, and the petals of its flowers are white. Whereas the Toothcup species have leaves that clasp their stems, the leaves of Wheelwort are sessile.