Blue Butterfly-bush (Psoralea pinnata)

Psoralea_pinnata_Abu Shawka
Photo: Abu Shawka

Family: Fabaceae

Growth Habit: Erect shrub to small tree with groups leaves up to 5 cm long crowded together at the tips of branches. The leaves have 5-11 very narrow needle-like leaflets, 2-4 cm long and 0.8-2mm wide. The upper surfaces are channelled and both surfaces are somewhat hairy.

Type of Plant: Erect shrub to small tree from 1-4m high

Stickpen
Photo: Stickpen

Flowers: White to lilac-blue ‘pea-shaped’ flowers, singularly or arranged in clusters in the leaf forks near the tips of the branches. Flowering occurs in spring and summer.

Fruit/Seed: Small egg-shaped pods, 3-4 mm long that turn from green to black when mature with 1 dark brown seed.

Dispersal: Spread by water, garden waste, contaminated soil, machinery birds, ants and mammals. Seedbank can persist in the soil for more than 8 years.

Distribution: Common in coastal and sub-coastal areas of Tasmania.

Status: Undeclared in Tasmania but considered an Environmental Weed.

Weed Impact:

  • Can form dense thickets, shading out understorey species and potentially impeding regeneration of overstorey species.
  • Can fix nitrogen, which can change the soil fertility and therefore suitability for native species, impacting their persistence in the long term.
  • Reported to be becoming a problem in forestry in some states.

Control Methods:

  • Hand pull or dig out seedlings and young plants.
  • Cut and pain with glyphosate larger, mature plants.
  • Spray foliage of any resprouting material with diluted glyphosate.
  • Monitor site for germinating seedlings for at least 8 years.

N.B. Always check the herbicide label before use.