decayed petals.

[rosko]

Ok, I see !

I had already noticed there are 2 different sorts of flowers on this plant. I didn't know about sterile ones.

So, this is why the structure persists : true petal is more delicate and fragile while bractée is tougher/coriaceous.

Thanks, Bjørn, for this clarification !

[Bjørn Rørslett]

Actually, depending on the species, there might not be petals at all, just the bracts. Also do note that the normal flowers, ie. those without bracts, have large nectaria. You can see the glistening nectar fluid oozing out of the nectaria in my picture.

[Akira]

Bjørn, thanks for the explanation.  I'm always fascinated by the way different species develops themselves differently according to the environment.

[rosko]

Akira, I have to apologize for the peremptory way I answered to your comment : bract is not petal, even I it looks like petal (shape, color, etc.), and even if it is called ''floret''.

So the structure left after a whole winter is probably cellulose, a vegetable fiber which constitute the skeleton of any plant.

[Fons Baerken]

the infertile flowers that lure the insects

[Akira]

Akira, I have to apologize for the peremptory way I answered to your comment : bract is not petal, even I it looks like petal (shape, color, etc.), and even if it is called ''floret''.

So the structure left after a whole winter is probably cellulose, a vegetable fiber which constitute the skeleton of any plant.

Francis, no worries!  This little discussion was very fruitful.

[rosko]

the infertile flowers that lure the insects

Well, I don't see what purpose for, if the flowers are no fertile ? They may attract insects from very far due to their size and then eventually insects land on scented fertile flowers...That is an assumption.

[Akira]

Well, I don't see what purpose for, if the flowers are no fertile ? They may attract insects from very far due to their size and then eventually insects land on scented fertile flowers...That is an assumption.

My wild guess is that the bracts either reflect or absorbs UV to guide the insects to the central part of the flower head.  Or, they just function as intermediate steps for the pollinators to crawl onto the flower head?

[Bjørn Rørslett]

Human speculation on the ways Nature operates and functions tends to be futile and a waste of time. We can only assume that because an entire genus with 70-80 species share this structure, it does not prevent natural selection and evolution .... Besides, even bigger genera such as Euphorbia (spurges) have even more advanced variants of the same underlying principle.

UV photography indicates the sterile bracts are moderately UV reflective and that the nectaria are UV bright. They also fluoresce under UV. The entire Carrot familiy (Apiaceae) shows the identical pattern.

[Fons Baerken]

you are basically saying the same thing ,
refrasing a similar assumption, amazed i am one takes words for absolute
rather than relative or provisional really

[Bjørn Rørslett]

Thus we all reach unison agreement. Good for everyone.

[Gary]

Great viewing and interesting read.  Thank you all.