A mystery to me?

I have this plant growing in a pot and I am assuming it isn't a weed! I say assuming because I don't know what it is? Last year I tried what I thought were some kind of clematis seeds. I think it was supposed to be a yellow flower and the word 'wheel' rings a bell! They resembled this plant but all eventually failed. Then this year this popped up in the compost!
Any ideas? It started growing late spring.

 

I can't get a big enough pic on my little screen but it almost looks like a Buddleia to me.

 

Hi, here is a closer pic of a branch. The leaves look weedish to me. The flowers/seed heads are really tiny!

 

Interesting looking thing. How tall has it grown?

 

Hi, it is about 2' tall now. If I remember last year correctly, after these tiny flowers the plants just started deteriorating.
p.s. these are the seeds I planted last year
Clematis tangutica Pinwheel
Gazania

 

I think it's a young Buddleia.

 

If it is a buddlia I wonder what it is doing in my compost? It still might be the pinwheel but I can't find any pics of young pinwheels to compare.
I shall compare leaf shapes on the internet and see what I can find.
many thanks
Gazania

 

I'm having no luck. This has to be a weed of some sort!
Gazania