Thyme-Leaved Sandwort
Arenaria serpyllifolia
Pink family (Caryophyllaceae)

Description: This annual plant has stems 6-10" long that are ascending or sprawling. These stems are round, dark purple, and finely pubescent. Multiple stems are produced from the base of the plant, otherwise they are little branched. The opposite leaves are widely spaced along the stems. Each leaf is about " long and a little less across. It is ovate, smooth along the margins, and slightly ciliate. The upper stems terminate in small clusters of flowers; these flowers bloom only one or two at a time on pedicels about " long. Each flower is about 1/5" (4 mm.) across, consisting of 5 white petals, 5 green sepals, 10 stamens, and 3 styles. The petals are unnotched at their tips, while the sepals are lanceolate, slightly pubescent, and longer than the petals. The blooming period occurs during late spring to early summer and lasts about 1-2 months. The seed capsules are ovoid, the same length or a little shorter than the sepals, and firm in texture. Each capsule has 3 bifurcated teeth (appearing to be 6 small teeth) along its upper rim. It contains several seeds with pebbly surfaces that are gray-black and reniform. The root system consists of a taproot. This plant reproduces by reseeding itself.

Cultivation: Full sun, mesic to dry conditions, and poor soil are preferred. While this plant can grow in more fertile soil, it has trouble competing with taller, more aggressive plants.

Range & Habitat: The adventive Thyme-Leaved Sandwort is a fairly common plant that occurs in many counties of Illinois, except for the NW and south-central areas of the state (see Distribution Map). It is native to Europe. Habitats include rocky glades, cliffs, fields, cracks in sidewalks and along curbs, barren areas along railroads and roadsides, and sunny waste areas that are gravelly or sandy. This plant prefers disturbed habitats with scant vegetation; in Illinois, it continues to spread into new areas.

Faunal Associations: The small white flowers probably attract Syrphid flies and small bees. The relation of this species to birds and mammalian herbivores is not well understood.

Photographic Location: Several plants were growing from the cracks of a sidewalk curb in Urbana, Illinois.

Comments: Thyme-Leaved Sandwort is a fairly common little plant that grows in obscure corners of the landscape. Because of its small stature and nondescript appearance, it is frequently overlooked by passersby. What distinguishes Thyme-Leaved Sandwort from the similar-appearing Stellaria and Cerastium spp. (Chickweeds) is the structure of their flowers: the Chickweeds have petals that are notched at their tips, unlike the petals of the former. The other Sandworts that occur in Illinois have been reassigned to the Minuartia genus and the Moehringia genus. These Sandworts also have unnotched white petals, but their leaves are either smaller in size or linear in shape. Many of these species have flowers that are slightly larger and showier than those of Thyme-Leaved Sandwort.