purpletop, cluster flower vervain, tall verbena
This is a purple flowered herb with erect stems up to 2m tall which are conspicuously square in cross-section and rough.
Leaves are sessile (without a stalk), dull green and also rough. Leaves are narrowly rectangular to pear-shaped and hairy. The base of the leaf is slightly stem-clasping, leaf margin is irregular to regular toothed and apex is tapering to a point.
Inflorescence (a group of flowers) occurs in the end of the branch having small purple-mauve flowers on cylindrical flowerheads grouped in threes. Flowers in late Spring and throughout Summer.
Fruit is a mericarp meaning that one segment of a fruit breaks at maturity into units. The seed is tiny and is progressively realeased from the base to the top of the seedhead.
Other plants easily confused with this plant
There are a number of species of Verbena all with stems with a square cross section. A number are weeds of disturbed areas. Many are native to South America, some originate in the Mediterranean.
A species native to Australia is Verbena gaudichaudii which only grows to 1 m and has pale pink to lilac flowers which are well spaced and rarely clustered. The leaves have a short stem.
Sources & References
"Weeds - an illustrated botanical guide to weeds of Australia" by B. A. Auld and R. W. Medd
"Plantnet FloraOnline" (2005) http://plantnet.rbgsyd.nsw.gov.au/
Prepared by Justin KY Chu, July 2005
Checked by IEWF, December 2006