Porlieria angustifolia aka Texas Lignum Vitae

Porlieria angustifolia is a shrub or small tree from Texas and eastern Mexico. It belongs to the Zygophyllaceae family. Common names include Texas porlieria and soap bush. Kew places it in desert and dry shrubland habitats. The RHS lists it as non-native to Britain and Ireland. Its native range and habitat place it among dryland woody plants.

This plant forms a dense crown with many branches. Its crooked limbs give the crown a broad shape. Virginia Tech gives a height of 10–15 feet [3–4.6 metres]. The same account describes both shrub and small-tree forms. Young bark is pale gray and smooth. As the bark ages, it darkens and grows rough. The slender twigs are gray-brown. They bear many short, knotted spur shoots. These shoots also carry some of the leaves.

The evergreen leaves have a pinnate structure, with leaflets along a central axis. Each leaf measures about 1½–3 inches long. Leaves grow in opposite pairs or crowd onto spur shoots. Each has six to eight pairs of small leaflets. The leaflets are lance-shaped and often curve. Both their upper and lower faces are dark green. A groove runs along the leaf stalk. The leaflets fold at night, changing the foliage's appearance. Their small size contrasts with the plant's dense branching.

Bright purple flowers appear after rain, potentially throughout the year. This links flowering to rain rather than one fixed season. Each flower measures about half an inch across. Five broad petals form the flower. Long flower stalks arise from the leaf axils. Flowers may stand alone or form small groups. Their color provides a contrast with the dark green leaves.

The fruit is a flattened capsule with a heart-like outline. It measures about one inch long and has two to four lobes. Its surface is glossy and reddish brown. In fall, the capsules split and release shiny red seeds. The flowers, fruit, and evergreen foliage provide several visible features across the year. The supplied accounts describe its dry native habitat but give no detailed garden care. They do not establish cold hardiness, soil needs, or watering schedules. They also provide no evidence about edible parts or toxicity. No specific pests or diseases appear in these accounts.