Knapweed ID

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bankst
Posts: 69
Joined: Thu Jul 31, 2008 9:50 am

Knapweed ID

Post by bankst »

Knapweed ID:

Lots of Knapweed in flower at the moment, most of it presumably the Common Knapweed, Centaurea nigra.

However, Anno and I were on a former industrial site near Runcorn Docks yesterday and noticed these specimens growing on limestone ballast. The presence nearby of Common Centaury, Centaurium erythraea, made us wonder if this might just be the Chalk Knapweed, C. debeauxii? I haven't a clue how you tell the two knapweeds apart, although some chap called Stace apparently knows the secret, (Flora of the British Isles, Edition 3). If only I had a copy to hand. Any ideas?

Tom.

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Centaurea 2.jpg
Centaurea 1.jpg
Graeme
Posts: 36
Joined: Tue Mar 24, 2009 2:49 pm

Re: Knapweed ID

Post by Graeme »

Looks like a good candidate to me.

The stem is only slightly swollen under the flower head and the central part of the phyllaries (the bits in the brown part) is lanceolate not ovate. Arthur Chater says if you can see the green underpart between the phyllaries it is a good indicator and that is quite clear in your photos. Still, they are not easy, so no money on it!

Graeme

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