Veronica filiformis

Veronica filiformis is a species of flowering plant in the genus Veronica. It is known by many common names, including slender speedwell, creeping speedwell, threadstalk speedwell and Whetzel weed. It is native to eastern Europe and western Asia, and it is known in many other regions as an introduced species and a common weed.

V. filiformis is a rhizomatous perennial herb producing mats of hairy stems that readily root at nodes that touch substrate. It is self-sterile and rarely seeds, being spread by stolons.

The corolla of V. filiformis is four-lobed and blueish with a white tip, around 8–10 mm in diameter, the top lobe being largest since it is actually a fusion of two lobes. At the center are two long, protruding stamens. 

Solitary flowers occur in leaf axils. They are on relatively long, slender stalks that arise from the leaf axils, and appear between April and July. The leaves, found near the base of the stem, are 5–10 mm across, rounded or kidney-shaped with blunt teeth and short stalks, and smaller on distal parts.It is perennial. In Ireland, the plant was sewn into the clothing of travellers for good luck.

A native to northern Turkey and the Caucasus, V. filiformis was introduced to the United Kingdom from Turkey in 1808 as a rock garden plant and was first reported as an escape in 1838. It was introduced to the United States nursery trade in the 1920s and is now generally considered a weed. 
It can be invading of lawns, sod, and turf, and has become naturalised in gardens and grassy paths and on roadsides. It prefers shade, moist soils, good fertility and a low mowing height, and due to the speed at which is spreads, it is often necessary to use herbicides to remove it.