Blackstonia perfoliata aka Yellow Wort

Blackstonia perfoliata, or yellowwort, belongs to the gentian family, Gentianaceae. It is an annual plant of temperate regions. Its native range spans Europe, the Mediterranean region and Iraq. It grows wild in Britain and Ireland. Its range also includes parts of North Africa and western Asia. Chlora perfoliata is another name used for this species.

Yellowwort forms clumps with paired leaves along the stems. The leaves have pointed tips and a waxy surface. Their colour ranges from grey-green to blue-green. Each pair joins at the base, enclosing the stem. This gives the stem the look of passing through the leaves. The RHS describes plants reaching about 1.3 feet [0.4 metres] tall. Its garden size range reaches 1.6 feet [0.5 metres] in height and spread. The foliage is deciduous.

The flowers are yellow, with a cup-like shape. Each bloom has six to eight petals. Flowers appear through summer and autumn, then close in the afternoon. The yellow blooms contrast with the grey or blue-green leaves. These leaf and flower traits help identify the plant. Its wild habitats include chalk grassland, limestone grassland and dunes. It also grows in rocky sites.

In gardens, give yellowwort full sun and soil that drains well. Neutral or alkaline soil suits it. The RHS lists chalk, loam and sand as suitable soil types. Its moisture range runs from dry to moist. South-facing and west-facing sites suit its light needs. It can grow in exposed or sheltered positions. The RHS gives it the UK hardiness rating H7. This rating covers the coldest European continental conditions. Grow new plants from seed; no pruning is needed.

Yellowwort suits coastal gardens, cottage gardens and informal planting. It also fits wildflower meadows and wildlife gardens. These uses reflect its grassland and dune habitats. The RHS reports few problems with pests or disease. Plants For A Future records no weed concern. The plant can supply an extract used as yellow dye. That source lists no known food or medicinal uses. It also records no known hazards. This does not establish that the plant is safe to eat.