What Does It Look Like?
What is it?
Snakeweed (Stachytarpheta spp.) is a clumping perennial shrub which grows up to 2 m high from a single white woody root-stock. The stems are tough and widely branched, with opposite, lance shaped leaves up to 10 cm long and attached to the stems by short stalks (petioles). Leaf margins are crenate to serrate. The flowers are formed along stiff spikes, up to 50 cm long and 0.5 cm wide. The distinctive shape of these spikes gives these weeds their name.
Each flower is about 0.5 cm wide and has 5 petals that fuse to form a tube at their base. Flowers bloom in rotation from the bottom of the spike upwards and wilt soon after being picked. Flower colour varies with the species and may be white to pale blue, light blue, dark blue to purple or pink. A pointed bract protects the point where the flower joins the spike.
After flowering the spikes dry off and the seeds develop beneath the bracts. The seeds are dark brown to black and 4-6 mm long (Smith 1997).
For further information and assistance with identification of Snakeweed contact the herbarium in your state or territory.
Pink, Red, Purple, Blue, White
Growth form (weed type/habit)
Where it currently grows? Preferred habitat
Snakeweed prefers areas where average rainfall exceeds 1000 mm (Parsons & Cuthbertson 2001). It is reported to prefer waterways and adjacent pasture areas (Smith 1997), disturbed areas including roadsides, and over grazed pastures, and monsoon forest disturbed by pigs and buffalo (Institute of Pacific Forestry 2007) and sometimes cultivated fields (Parsons & Cuthbertson 2001).
Are there similar species?
Snakeweed (the genus Stachytarpheta) is very distinctive and not easily confused with other genera. The various species of Stachytarpheta could be confused with one another. Navie (2004) provides the following features for differentiation:
Stachytarpheta australis has pale blue or almost white coloured flowers about 5 mm in diameter that are borne on relatively robust flower spikes about 3-5 mm thick. Its stems and lower leaf surfaces are hairy an dits leaves have a somewhat wrinkled appearance with sharply toothed margins.
Stachytarpheta jamaicensis has pale blue, blue or mauve coloured flowers to 8 mm in diameter that are borne on relatively robust flower spikes 3-5 mm thick. It stems and leaves are totally hairless and its leaves are slightly fleshy in nature and sharply and deeply toothed margins.
Stachytarpheta cayennensis has dark blue, purple, or violet coloured flowers about 5 mm in diameter that are borne on slender flower spikes 1-3 mm thick. Its stems and leaves are almost totally hairless and its leaves have a wrinkled appearance with sharply, and deeply toothed margins.
Stachytarpheta mutabilis has pink to reddish coloured flowers, 10-12 mm in diameter, borne on robust flower spikes up to 7 mm thick. Its stems and both leaf surfaces are densely covered in hairs and its leaves are velvety in texture with sharply, but finely toothed margins.
These Snakeweeds are also relatively similar to common verbenas (Verbena litoralis and Verbena officinalis) and Chaff Flower (Achyranthes aspera) as these species also have very elongated flower spikes. The flowers of chaff flower are greenish-coloured and lack obvious petals and the leaves have entire margins. The verbenas have four fully developed stamens instead of the two in the Snakeweeds, and smaller flowers that are less than 4 mm in diameter.