Veronica peregrina aka Necklaceweed

Veronica peregrina produces tiny, four-lobed flowers only about 2 to 3 millimetres across, usually white but sometimes pale lavender or faintly pink. They are arranged in loose terminal racemes on very short pedicels and are bilaterally symmetrical. Each individual bloom is short-lived — flowers commonly wilt and fall the day after they open and are replaced by new ones the following day — and is followed by a small heart-shaped to oblate capsule containing many minute seeds.

Two subspecies are generally recognised. Subspecies peregrina is the typical, essentially hairless form and is considered native to the Americas, including New England. Subspecies xalapensis is densely glandular-hairy and is treated as introduced from Europe in some North American floras while occurring widely in California and Latin America. The species also goes by many regional common names — purslane speedwell, neckweed, American speedwell, wandering speedwell, necklace weed and equivalents in French, German, Spanish, Italian, Japanese and Russian.

Folk and ethnobotanical records ascribe limited medicinal value to the plant. Decoctions of the whole herb have been used as an emmenagogue and haemostatic, and reputedly to "promote the knitting together of broken bones," with reported applications including dysmenorrhoea, fractures, haemoptysis and traumatic injuries. The Navajo traditionally used the plant ceremonially as an emetic and in hunting rituals. Plants For A Future rates its medicinal value at 2 out of 5, and there is no modern clinical evidence supporting these uses.

Veronica peregrina has no recorded culinary uses. Both Plants For A Future and Useful Temperate Plants record "no edible parts known," and the species is not consumed traditionally as a food.

No commercial or material uses (fibre, dye, fodder, ornamental, cover crop, etc.) are recorded for Veronica peregrina. Both Plants For A Future and Useful Temperate Plants explicitly list no other uses, giving the species an "other uses" rating of 0 out of 5.

Propagation is by seed only. Plants are direct-sown where they are to grow, with sowing in spring or late summer giving the best results; no special pre-treatment is needed. Because the flowers are hermaphrodite and self-fertile, single plants set viable seed prolifically and the species typically self-sows once established.

Outdoors V. peregrina thrives as a low, weedy annual in moist, disturbed ground in full sun. It tolerates a wide range of soil textures (sand, loam or clay) and pH values from mildly acidic to mildly alkaline, but prefers moisture-retentive yet well-drained soil and cool summers. In its native range it colonises pastures, streamsides, washes, marshy edges and forest openings up to about 3,000 metres, while in gardens it readily volunteers in lawns, vegetable beds, vineyards and even planter boxes wherever the soil stays damp.

The flowers are hermaphrodite and self-fertile, allowing the plant to set seed without insect visitors. The blooms are very small and inconspicuous and produce abundant seed via self-pollination, which contributes to its success as a colonising weed.

Specific pests and diseases of Veronica peregrina are not reported in the consulted floras and extension sources; the plant itself is more often treated as the problem, being widely classed as a "common and obnoxious weed" of lawns, gardens, fields and disturbed ground across its native and introduced ranges.