Stachytarpheta cayennensis

Stachytarpheta cayennensis.

Dark Blue Snakeweed, native to Central America, is naturalised in S.E. Queensland.

They are perennial shrubs 1 – 2 m high.
The young, greenish-purple stems are 4-angled.
Older, pale brown, woody stems are cylindrical.
Stems may have a few hairs near the nodes or none at all.

The opposite, ovate leaves are up to 10 cm long.
There are no hairs or only a few mainly on the midvein underneath.
The edge is deeply toothed and the tip pointed.
The veins are depressed on the upper surface giving a wrinkled appearance.

The inflorescences are narrow, erect, slightly curved spikes up to around 40 cm long.
The stalkless flowers are sunken into the main axis with a bract at the base of each.
Flowers open a few at a time starting at the base.

The flowers have a similar structure to those of S. mutabilis.
The corolla tube is around 6 mm long.
The corolla, around 5 mm across, can be dark blue, violet or purple.