Isotoma fluviatilis aka Isotoma

Isotoma fluviatilis is a low, evergreen perennial from Australia. Its native range covers the east and southeast. It belongs to the bellflower family, Campanulaceae. Common names include blue star creeper, laurentia, and swamp isotome. It grows beside creeks and streams in damp sand or mud. It also occurs near granite outcrops and in wet hollows.

The plant forms a close mat of small green leaves. Its runners take root as they spread across the ground. Garden plants reach about 0.17–0.33 feet [0.05–0.1 metres] tall. Their spread reaches about 1.6–2 feet [0.5–0.61 metres]. Growth proceeds at a moderate rate. Plants reach their mature size in one to two years. The green stems have no scent. Leaves have no hairs and vary from narrow to oval. Some lower leaves have a broader, egg-like shape. Their edges may be smooth or have rounded teeth. Each leaf reaches about half an inch long.

Small, star-shaped flowers rise on short stalks above the leaves. Their colour ranges from white to pale blue. Each flower grows alone and measures about a quarter-inch across. Flowers have four or five petals. Bloom runs through spring and into summer. Missouri Botanical Garden lists May to June as its flowering period. Small seed capsules follow, with fruit present in autumn. These uneven capsules widen toward the tip and reach a quarter-inch long.

Grow this plant in moist soil with good drainage. It suits soil with moderate fertility and added organic matter. RHS lists clay, chalk, loam, and sand as suitable soils. It also accepts acid, neutral, or alkaline conditions. Full sun and partial shade both suit it. Sources differ on cold tolerance. RHS assigns H3, for mild and coastal UK sites. US sources list USDA zones 6–8. Divide plants to raise new stock; they need no pruning.

Use it between paving stones, in rock gardens, or along pond edges. It also suits containers and planting beneath roses or shrubs. The mat tolerates light foot traffic. Runners may need deep edging to keep them within bounds. Care needs are low, with few major pest or disease problems. Slugs and snails can cause damage. Soil that stays too wet without drainage can cause root rot.