Arenaria serpyllifolia L.

Thymeleaf Sandwort

Arenaria serpyllifolia plant

Family - Caryophyllaceae

Habit - Taprooted annual forb.

Stems - Sprawling to erect, usually branched, moderately pubescent with minute, downward-curved hairs, sometimes also stipitate-glandular.

Arenaria serpyllifolia stemStem.

Leaves - Opposite, fused basally into a sheath, usually sessile. Leaf blades 0.2-0.7 cm long, elliptic to broadly ovate, tapered at the base, acute, entire, glabrous.

Arenaria serpyllifolia leavesLeaves.

Inflorescence - Axillary single flowers or terminal loose cymes. Pedicels elongating in fruit to 1 cm, retrorsely pubescent. Bracts paired, leaflike.

Flowers - Sepals 5, 2-3 mm long, becoming elongated to 4 mm long at fruiting, free or basally fused, lanceolate to narrowly ovate, sharply pointed, the margins thin and whitened. Petals 5, free, usually shorter than the sepals, 0.6-2.7 mm long, oblong, not tapered to a stalklike base, entire at the tip, white. Stamens 10, the filaments white, glabrous, distinct. Pistil with 1 locule, sessile. Styles 3, white, glabrous, each with the stigmatic area along the inner surface. Ovary superior, green, glabrous, 1.5 mm long, 1 mm in diameter, unilocular. Placentation free-central.

Arenaria serpyllifolia flowerFlower.

Arenaria serpyllifolia flower2

Arenaria serpyllifolia calyxCalyx.

Fruits - Capsules, 3.0-3.5 mm long, dehiscing apically by 6 ascending to recurved teeth. Seeds 10-15, 0.3-0.6 mm wide, kidney-shaped, the surface tuberculate, black.

Arernaria serpyllifolia fruitFruit.

Flowering - April - August.

Habitat - Glades, fields, bluffs, roadsides, railroads, disturbed areas.

Origin - Native to Europe.

Other info. - This tiny plant is common throughout most of Missouri and large portions of the continental U.S. It is small and inconspicuous, and often overlooked, although large populations can be showy in their own way on warm, sunny spring days. This species can be identified in the field by its small, opposite, ovate leaves and its small white petals, which are smaller than the sepals.

Missour plants can be subdivided into two varieties: var. serpyllifolia, which has more conical fruits and larger seeds, and var. tenuior, which has more cylindrical fruits and smaller seeds. The distinction is subtle and only possible if mature fruits are present (or by counting chromosomes).

Photographs taken in Gainesville, FL., 2-11-03, and at Providence Prairie, Lawrence County, MO., 6-18-05 (DETenaglia); also along the Katy Trail west of Augusta, St. Charles County, MO, 5-12-2017 (SRTurner).