Australian fireweed“Write about fireweed” said a friend, “I’ve got it growing all over the place”.

But ’fireweed’ is one of those all-embracing terms which attaches itself to different plants in different places.  And all these plants have one thing in common – they are the first to colonise soils exposed by forest fires or forest clearing.  They need light, moisture and, preferably, mineralised soil which has been exposed when the top layer has been burned or scraped away.  Their small seeds are all wind dispersed.

For those living in the Northern Hemisphere, fireweed is most likely to be Chamerion angustifolium, with rosy pink flowers, growing at least a metre high.  Preferring colder climes, in the US it is found from Alaska south, but less likely to be found in the Southern States.  In the UK it is well known as Rosebay Willowherb, prompt coloniser of bomb sites in war torn London during WWII.  It’s even the national flower of the Yukon.  Not apparently poisonous, but leaves and rhizomes become bitter as the plant matures.

In Australia and New Zealand it belongs to quite a different family – the Senecio (which also includes that well known pest Ragwort) and all varieties have yellow flowers, and are poisonous to animals.

My website and weed book searches produced more confusion.    Confined mainly to Australia’s east coast is a fireweed named as Senecio madagascariensis, which has now spread to cover many hectares of coastal pastures, causing reduction in pasture quality and growth rate reduction and death in cattle and horses.  But my weed book (An Illustrated Guide to Common Weeds of New Zealand, 2nd ed) quotes ‘Australian fireweed’ as Senecio bipinnatisectus, and from the pictures they are quite different.  The former has lanceolate leaves which are not deeply dissected, while the latter has deeply dissected leaves which get progressively ‘frillier’ at the plant grows.

Madagascariensis has many petalled small daisy like flowers and grows to around 70cm, while Bipinnatisectus has tiny (2mm) greenish yellow disks with no petals, growing upwards in a loose inflorescence, and the plant can reach 2 metres tall.

Just to complicate things still further, there are several native fireweeds which are common in waste places.  Senecio glomeratus is a hairy beast with white woolly hairs on both leaf surfaces and can tolerate both waterlogged and very dry habitats.  Senecio minimus  has hairless lance-shaped leaves with regular teeth on the margins and is most commonly found on forest margins.  Senecio quadridentatus (also known as Cotton or white fireweed) has woolly-hairy linear leaves which are usually grey-green on the upper surface and white underneath and is always found on recently disturbed ground.

And now there’s another which has just been classified as indigenous to NZ.  It’s called Senecio biserratus Belcher and is often associated with dune systems where it grows amongst Muehlenbeckia complexa.

So if you’ve recently felled a pine plantation, or suffered a forest fire, or cleared some land, you may well find that a fireweed species is the first to regrow, and the sources I’ve consulted seemed reluctant in the extreme to say how to get rid of it!  However, all species seem to need full sun, so when shade arrives from competing species it is likely to give up or move on.  For chemical control you should consult your farm supplies experts.

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