Senecio madagascariensis
Common names
Fireweed, Madagascar ragwort
Biostatus
Exotic
Conservation status
Not applicable
Category
Vascular
Structural class
Herbs - Dicotyledonous composites
Simplified description
An erect, yellow-flowered annual or short-lived perennial daisy with narrow, non-fleshy, lanceolate leaves and a small fibrous root. It produces many small yellow-rayed flower heads whose outer (calycular) bracts are narrow, 0.5–0.8 mm wide. The small seeds are wind-dispersed.
Flower colours
Yellow
Detailed description
Annual or short-lived perennial herb, erect, upright and less branched than S. skirrhodon. Root system a small fibrous root. Leaves narrow-lanceolate, not fleshy, length:width ratio 5–12. Flower heads yellow-rayed. Calycular bracts narrow, 0.5–0.8 mm wide. Seeds small and wind-dispersed.
Similar taxa
Senecio madagascariensis is most likely to be confused with Senecio skirrhodon DC., a longer-established and largely non-invasive species. Senecio skirrhodon was first recorded as naturalised in 1920 and is found throughout New Zealand. The most reliable distinguishing character is the width of the calycular bracts, which holds regardless of plant condition: 0.5–0.8 mm in S. madagascariensis and 0.8–1.5 mm in S. skirrhodon. Senecio madagascariensis is an upright annual or short-lived perennial with a small fibrous root. Its leaves are narrow-lanceolate and not fleshy, with a length:width ratio of 5–12. Senecio skirrhodon is a perennial with a better-developed rootstock and a more divided, spreading, flaccid habit. Its leaves are broader, more velvety and often fleshy, with a length:width ratio of 3–9. Leaf shape and texture are less reliable on mown plants.
Distribution
The fireweed complex is native to Africa. True S. madagascariensis is a distinct lineage confined to Madagascar. The invasive lineage that carries the name elsewhere originates from continental southern Africa. Its exact source is unclear but possibly the Eastern Cape. This lineage is naturalised in Australia, Hawai’i, Japan and South America. The New Zealand, Australian, Hawaiian and Japanese populations belong to one lineage (Clade V), and the South American populations belong to another (Clade VI).
In New Zealand its presence was confirmed genetically in 2024. It is known from Te Tai Tokerau / Northland, where it has spread south since 2020 from Hokianga to south of Dargaville. It is also known from Cape Palliser Road, South Wairarapa. The Wairarapa population was first noticed by Pat Enright in 2022 and confirmed by morphology and genetic data in 2026. It may be more widespread than records indicate, because populations may have been overlooked or misidentified as S. skirrhodon.
Habitat
In Northland it grows in pasture in sand country, roadsides, quarries and forestry. At Cape Palliser it is scattered along roadside gravel and up into the gravel fans above the road. It favours disturbed, open, well-drained, low-competition ground.
Detailed taxonomy
Genus
Family
Taxonomic notes
New Zealand fireweed-complex plants were long all treated as S. skirrhodon until genetic data showed that two species are present (Schmidt-Lebuhn et al. 2024). A later global study found that Madagascan S. madagascariensis is deeply divergent from all continental African and invasive material (Schmidt-Lebuhn et al. 2025). The type of S. madagascariensis is Madagascan, so the invasive lineage would need another name if it were formally recognised as a separate species. Senecio ruderalis Harv. is the oldest available name, but the change has not yet been formally made.
Endemic genus
No
Endemic family
No
Other information
Etymology
senecio: From the Latin senex ‘old man’ (probably referring to the bearded seeds)
madagascariensis: “from Madagascar”
Referencing and citations
References and further reading
Dymock, J.J. & Winks, C.J. 2025. New Zealand Journal of Agricultural Research 68(7): 1799–1808.
Ford, M.; Shepherd, L. 2026. A new population of highly-invasive fireweed in southern Wairarapa, and a taxonomic complication. Trilepidea 264: 16–21. https://www.nzpcn.org.nz/site/assets/files/0/01/02/336/trilepidea_july_2026_final.pdf
Schmidt-Lebuhn, A.N. et al. 2024. New Zealand Journal of Botany 62(1): 1–13.
Schmidt-Lebuhn, A.N. et al. 2025. Biological Invasions 27: 243.
Webb, C.J., Sykes, W.R. & Garnock-Jones, P.J. 1988. Flora of New Zealand Vol. IV.
Wijayabandara, K. et al. 2022. Plants 11(1): 107.
Attribution
Factsheet prepared by M. Ford from Ford, M.; Shepherd, L. 2026. A new population of highly-invasive fireweed in southern Wairarapa, and a taxonomic complication. Trilepidea 264: 16–21. https://www.nzpcn.org.nz/site/assets/files/0/01/02/336/trilepidea_july_2026_final.pdf