COTTON THISTLE

Onopordum acanthium

Daisy & Dandelion Family [Asteraceae]

month8jul month8july month8aug month8sep month8sept

status
statusZneophyte
 
flower
flower8mauve
 
inner
inner8white
 
morph
morph8actino
 
petals
petalsZMany
 
stem
stem8round
 
stem
stem8winged
 
stem
stem8spines stem8thorns
spines
contact
contactZlowish
 

4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
A neophyte which is often found as a garden escapee and growing erect to 2.5m, much taller than the field full of Stinging Nettles surrounding it. Both leaves and stems are greyish-white with masses of appressed hairs, paler green where the hairs are fewer. It is branched.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
This specimen is wilting somewhat - the brush-like infloresence having turned pale-brown and some leaves also.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The stems have broad spiny wings along most of their length and a few long spiny leaves (10-50cm) which are similarly silvery-grey.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The flowers are solitary atop each branch.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The flowerheads are large, 20-60mm wide and very spiny. The greyish-white hairs covering the wings (and the leaves) are all laid flat and almost parallel as if combed from stem to the tips of the spines.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The flowerheads, like those of Woolly Thistle, are 'cobwebbed' in grey-white hairs between each neighbouring spine, but are not as spherical, being more oblate spheroidal in shape, shorter than wide (not counting the purple florets atop).


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The brush-like inflorescence seems little different to all the other thistles, apart from both size and colour (in the case of Creeping Thistle with its lilac-coloured inflorescence). It has disc florets with 5 long and narrow petals each, surrounding a single white to indigo-coloured style.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The style is often indigo coloured and protrudes out of the purple disc-floret 'petals'.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
White pollen grains.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The interconnecting mesh of hairs between each sharp spine - like the wiring of an old telephone exchange. Spines turning fawn-coloured at their tips.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
Your Author surmises that the web of cottony threads between the wiry green bracts on the flower head forms akin to the way drying Evoslurp™ glue dries: with a semi-viscous liquid between them at first, then, as the bracts grow and part from each other, the liquid is stretched whereupon the surface tension dictates that it forms threads between parting bracts, which then either dries, polymerises or oxidises into the threads seen, much as does Evoslurp™ glue when two recently coated surfaces are parted. It is possible the spiny bracts themselves exude the semi-liquid viscous fluid when they are all touching each other. The Author does not know if his theory is correct, but it seems logical Captain Kirk™. Spear Thistles, Woolly Thistle, Globe-Thistles and Cobweb Houseleeks also have networks of woolly threads between an array of bracts.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
The wings on the stems are broad, but not continous as some books say.the spines can be seen to extend from the stem all the way to their very sharp point through the wing.


4th July 2006, Bohemia Corner, Ventnor, IoW. Photo: (CC by 2.0) Geoff Toone
It seems plausible that the viscous stringy fluid theory also applies to the hairs on the wings: they seem to stretch along the direction in which the wing grows, so all end up parallel to each other.


Photo: (CC by 2.0) Geoff Toone
The basal leaves; stem not yet grown.


Photo: (CC by 2.0) Geoff Toone


Photo: (CC by 2.0) Geoff Toone
Basal leaves.


Easily mis-identified as : Woolly Thistle (Cirsium eriophorum) but that belongs in a differeing genus and differs from Cotton Thistle in the following ways:

  • The spiny heads are spherical (rather than oblate spheroid for Cotton Thistle), but still contain a cobweb of white hairs.
  • The stems totally lack wings (whereas Cotton Thistle has spiny wings)
  • The leaves are nowhere near as hairy and instead dark-green with very-pale-green midribs and long narrow ovate teeth ending in a short sharp spine (whereas Cotton Thistle has mostly grey-white leaves with triangular teeth - but still ending in a short sharp spine)
  • The flower head spines only protrude a short distance from the spherical mass of white cob-web hairs (whereas the spines protrude much further out from the cobweb hairs and are much greener and more rubust on Cotton Thistle)
Uniquely identifiable characteristics

Distinguishing Feature :

No relation to : Cottonweed (Achillea maritima), Common CottonGrass (Eriophorum angustifolium), Lavender-Cotton (Santolina chamaecyparissus), Cotton Deer Grass (Trichophorum alpinum) [plants with similar names belonging to differing families].


  Onopordum acanthium  ⇐ Global Aspect ⇒ Asteraceae  

Distribution
 family8Daisy & Dandelion family8Asteraceae

 BSBI maps
genus8Onopordum
Onopordum
(Cotton Thistles)

COTTON THISTLE

Onopordum acanthium

Daisy & Dandelion Family [Asteraceae]