Fireweed

Habit of fireweed

Flower and variable leaves

Flowers occur in a loose cluster at the end of  branches

 

Flower is made up of small flowers (florets) in the centre and ray florets surrounding 

Small yellow daisy-like flowers with 13 ray florets

Seedhead forming

Fruit is an achene that has a pappus of silky white hairs

Scientific Name

Senecio madagascariensis Poiret

Common Names

fireweed

Origin

Native of south-eastern Africa and Madagascar

Family

Asteraceae

Habit

It is an erect, invasive, glabrous (without hairs or scales) or sparsely hairy herb that grows up to 20-60cm high and is a perennial exotic weed. It may sometimes become woody, much branched, and shrub-like. Growth habit varies considerably depending on conditions. In harsh, dry conditions it acts as an annual and may be under 20cm tall with minimal branching and flowers. In ideal conditions it acts as a short lived perennial and can grow up to 50cm tall with numerous branches, large leaves and many flowers.

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Habitat

It occurs in NSW mainly east of the ranges near the coast, often associated with cattle pastures. It invades pastures and native vegetation and can withstand drought conditions. It is an invasive weed that quickly colonises heavily grazed, cultivated or neglected land during the autumn to spring period.  Ideal conditions for fireweed growth are dry summers followed by autumn and/or winter rains.

General Description

Stems and Leaves:

The leaves are alternate, narrow-lanceolate to elliptic or oblanceolate. They are generally bright green and glabrous (smooth) and have margins that are lobed, serrate (asymmetrical teeth) or entire. The broader and longer leaves are stem clasping and fleshy and are 2-7cm long and 3-10mm wide but occassionally reach 8-10cm in length on vigorous and older plants. The stem is glabrous (smooth).

Flowers and Fruit:

The flowerheads (capitula) are small, yellow and daisy-like and are from 1-2cm in diameter and can number from 2-200 per plant. The inflorescence is a loose corymb (all the flowerheads are at the same level even though their stalks arise at different levels).  The flowerheads are made up of tubular (disc) florets and ray florets. The flowerhead has a fairly constant number of bracts (phyllaries) 20-21 in one row and of the same length. The number of ray florets is usually 13. Flowering occurs mainly from April to September.  The fruit is an achene (a dry indehiscent 1-seeded fruit) that is 1.5-2.5mm long and brown in colour. It has a pappus (the appendages, hair or scales at the top of the seed) that is 4-6.5mm long. Its seeds are 1.5-2.5mm long, light and slender with short hairs in longitudinal lines. The cypsellas (seeds) are cylindrical in shape, and crowned by a pappus of fine, silky white feathery hairs.

Distinguishing characteristics

The plant has an infloresence which has 13 ray florets and a fairly constant number of bracts 20-21. The plant is generally low, and heavily branched. The leaves are bright green and alternate with the longer leaves being stem clasping.

Senecio lautus (variable groundsel) can be distinguished from S. madagascariensis as the involucre (the whorl of bracts surrounding the inflorescence) is more than 4mm in diameter whereas it is 4mm or less in S. madagascariensis. The involvcral bracts of Senecio lautus are fewer in number (12-20), have narrow brownish tips, papery margins and are covered with very short, white hairs. The seeds (cypsellas) of S. lautus are usually densely hairy. Senecio guadridentatus is found in all states of Australia except N. Territory and grows in disturbed situations especially after fire. It is widespread. S. guadridentatus is a silver-greyish, erect, perennial herb that grows up to 1m high. The surface of the plant is covered in dense, white hairs. The leaves are 5-12 cm long and are linear to lanceolate. The flowerheads are narrow and cylindrical, 1-2mm in diameter in loose terminal clusters. These features distinguish it from Senecio madagascariensis.

Sources & References

Auld BA, Meld RW (1992) 'Weeds an illustrated botanical guide to the weeds of Australia.' (Inkata Press: Melbourne)

Harden GJ (Ed) (2002) 'Flora of New South Wales.' (University of New South Wales Press Ltd: Sydney, Australia)

Whittet JN (1958) 'Weeds - the farmers handbook series.' (V.C.N. Blight Government Printing: Sydney)

Allan H, Launders T, Walker K (2001) 'Fireweed' www.agric.nsw.gov.au

QLD Department of Natural Resources (2004) 'Fireweed' www.nrm.qld.gov.au

Sindel B (2003) 'Fireweed - A good weed'

 

Prepared by Kylie Pethybridge, 2005

Checked by Carole Campbell, 2005

Updated by Justin KY Chu, July 2005

Checked by Dr Peter Michael, July 2005