["Followup-To:" header set to rec.gardens.]
On Thu, 27 Jun 2013 05:47:06 +0000 (UTC), Danny D. wrote:
On Wed, 26 Jun 2013 15:42:03 +0000, Kay Lancaster wrote:

I control it here in my Oregon yard with heading the flowers**
as soon as I see them, and spot applications of glyphosate on
established plants in the fall.

Hi Kay,

I have 5 gallons of concentrated 40-something percent glyphosate, so,
I do have plenty to go around ... but what does "heading" mean?

Gads! That's a 500 year supply for me!

I guess that means to chop off the purple 'ball' at the top?
http://www1.picturepush.com/photo/a/...g/13420064.jpg

Not just the purple, but the green "ball" underneath it. That's where
the seeds are going to form.


What about the green balls that look slightly different?
http://www2.picturepush.com/photo/a/...g/13420070.jpg

Thistles are members of the Asteraceae, also known as the Compositae,
a very large family where the individual flowers are often mistaken
for "petals". The seed forming portion of the flower, the ovary, is
underneath the actual flower, and inside that cluster of overlapping
green bracts. And there can be literally thousands of flowers in one
of these "flower-looking" inflorescences (cluster of flowers).

If you think of a dandelion "flower", it's a disk about an inch or so
across when blooming. There are lots of little green leafy things
surrounding each "flower", that are really bracts, modified leaves.
http://newfs.s3.amazonaws.com/taxon-...-ahaines-b.jpg shows the greenish and brownish bracts on red-seeded dandelion,
a species you probably haven't met. And then you can see the yellowish
things that most people think of as petals, but they're actually
complete flowers... just a whole bunch of them gathered up together.
http://newfs.s3.amazonaws.com/taxon-...-ahaines-a.jpg See those sticky-up things with a double curlicue
at the tip? those are the tips of the pistil, which, like the mustard, is
a compound ovary with two carpels -- the curls are the stigmas of the flowers.
T

Here's a photo of a single dandelion flower: http://www.plingfactory.de/Science/A...nzelbluete.jpg
The curls at the top are the stigmas, and then just below that, you'll
notice a thicker yellow ring. That ring is 5 stamens, fused together
by their anthers, into a ring around the style of the pistil. http://www.inhs.uiuc.edu/~kenr/Photos/Taraxacum2.jpg Inside the ring of stamens is the
"neck" of the pistil, called the style, and way down at the
bottom of the flower, you'll see something that looks like a small white
sunflower "seed", which is the ovary of the flower. The white fluff is usually
interpreted as sepals, modified into seed hairs. The flat yellow thing over
to one side is actually 5 petals, fused together through most of their length
if you look at a dandelion flower you'll see that the "petals" look
like they've got teeth, and those are the tips of the real petals.
http://farm5.staticflickr.com/4038/4...8b088dfe_z.jpg

So whole flower-like inflorescence has multiple flowers crowded in it (why? Probably because it's easier for pollinators to spot a big clump of little flowers than single little flowers. It also spreads the bloom time, lengthening
the time when there's a chance a pollinator might pollinate it and you'd
get seeds forming. Once all the flowers in the head have bloomed, the
bracts close up, and you get the narrow fluff-end stage as the petals
and stamens dry up and the pistils start maturing their seeds.
http://www.cepolina.com/photo/nature...mus-flower.jpg
And finally, when the seeds inside the fruits are mature, the
bracts drop once again and you get the fluffball stage:http://i00.i.aliimg.com/wsphoto/v0/7...pping-E007.jpg where you can see the white hairs that were WAY down
in the real flower making the downy parachutes for the matured fruits,
the brown seeds.

Anyhow, your thistle heads are put together similarly, but a little
different. And each of the groups of fluff are going to have a seed
attached to parachute onto some new bare ground and possibly start
yet another thistle. http://www.backyardnature.net/n/09/090906cc.jpg

So that's probably more than you've ever wanted to know about the
structure of Asteraceae inflorescences, or as most people think
of them, "flowers". There's an incredible amount of variation
in structure of flowers and inflorescences in the Asteraceae, and
thistles and dandelions are just part of the story.

Oh yeah, sometime when you're really bored, ask me about dandelion sex.

Kay