Eupatorium cannabinum
Environmental Weed (2024)
Common names
hemp agrimony
Biostatus
Exotic
Category
Vascular
Structural class
Herbs - Dicotyledonous composites
Simplified description
Tall upright herb with downy hairy branches up to 2 m tall, leaves in pairs, stalked and divided into 3 segments, each with toothed edges, flowerheads a flat mass of small pink flowers on top of each stem.
Flower colours
Red/Pink, Violet/Purple, White
Detailed description
Perennial herb with a woody rootstock, shoots erect 0.3-2 m, simple or short branched, downy striate. Basal leaves oblanceolate, petiolate; cauline leaves subsessile, 3 (-5)-pinnate with elliptic-acuminate toothed pinnae 5-10 cm, short glandular-hairy. Inflorescence a dense terminal corymb, each head with 5-6 reddish-mauve to white florets, 1-2 mm diameter and c. 10 oblong purple-tipped involucral bracts c. 6 mm. Achenes blackish, 5-angled, gland dotted, pappus whitish.
Similar taxa
Not similar to other wetland plants with possible exception of Bidens spp. that lack hairs and have coarser toothed leaflets.
Distribution
Locally well established in South Taranaki and Wanganui District.
Habitat
Wetlands and riparian margins of water bodies, particularly areas that are rich in Nitrogen.
Conservation status
Not applicable
Detailed taxonomy
Genus
Family
Endemic family
No
Ecology
Flowering
January - March
Fruiting
Autumn
Year naturalised
1975
Origin
Eurasia, North West Africa
Reason for introduction
Ornamental plant
Control techniques
Not controlled in New Zealand.
Life cycle and dispersal
Perennial. Produces thousands of tiny wind dispersed seeds. Also has the potential to spread by water and contaminated machinery, deliberate planting.
Wetland plant indicator status rating
Information derived from the revised national wetland plant list prepared to assist councils in delineating and monitoring wetlands (Clarkson et al., 2021 Manaaki Whenua – Landcare Research Contract Report LC3975 for Hawke’s Bay Regional Council). The national plant list categorises plants by the extent to which they are found in wetlands and not ‘drylands’. The indicator status ratings are OBL (obligate wetland), FACW (facultative wetland), FAC (facultative), FACU (facultative upland), and UPL (obligate upland). If you have suggestions for the Wetland Indicator Status Rating, please contact: [Enable JavaScript to view protected content]
FACW: Facultative Wetland
Usually is a hydrophyte but occasionally found in uplands (non-wetlands).
Other information
Etymology
eupatorium: Commemorating Mithridates Eupator, king of Pontus and Armenia Minor in northern Anatolia (now Turkey) from about 120–63 BC, who is said to have discovered one of the species as an antidote for poison.
cannabinum: Like Cannabis, hemp
Environmental Weed (2024)
This plant is named in a list of 386 environmental weeds in New Zealand 2024 prepared by DOC. 759 candidate species were considered for inclusion on this new comprehensive list of environmental weeds in New Zealand. The species considered were drawn from published lists of weed species, lists of plants that must be reported or managed by law if observed, existing national and regional programmes and agreements for pest management, and species already managed by the Department of Conservation (DOC). Candidate species were then assessed to see if they were fully naturalised and whether they have more than minor impacts in natural ecosystems. Read the full report here.
Referencing and citations
References and further reading
Clapham, A.R.; Tutin, T.G.; Warburg, E.F. (1962). Flora of the British Isles. Cambridge University Press, Second Edition. 1269pp.
Webb, C.J.; Sykes, W.R.; Garnock-Jones, P.J. (1988). Flora of New Zealand Volume 4: Naturalised pteridophytes, gymnosperms, dicotyledons. Botany Division, DSIR, Christchurch.
Attribution
Factsheet prepared by Paul Champion and Deborah Hofstra (NIWA).