Hello
Your plant is Rhodiola rosea (Sedum rosea).
The male plants have yellow flowers and the female have red.
It is native here in the north of Sweden.

Here is a link that might be useful: Lili-Ann´s garden

Thank you for your comments liliann. (You have beautiful pictures, by the way!)
I have another reference (which I couldn't find the other night) which implies that the plants are monoecious, but that male flowers are yellow, while female flowers (on the same plant, and I think it was implied in the same flower cluster) are red.
What's the definitive reference, anyone? Is the species really monoecious or dioecious?

Well, doing some googling, I found another site that says it's dioecious.
(Now that I think about it, the idea that the plant is monoecious may have been what I was told by someone, or perhaps read in another forum...)

Also, another of my books says it is dioecious, but with "corymb- or umbel-like heads of numerous male or female, yellow-green flowers" - no mention of red flowers at all for Rhodiola rosea (yet another synonym). The same book mentions a subspecies integrifolia with "smaller leaves, and red-purple, sometimes green flowers".

Hmm, for the population that occurs here, it's puzzling that female plants would seemingly outnumber the male plants to such a degree that some popular guides don't even mention the male plants with yellow flowers. Odd.

Anyway, I guess I'll continue to assume it's what I thought it was originally! Thank you for the information, liliann.
(By the way, does any other plant have as many synonyms as this one?)

Hello again
Referenses for my answer is to be found in English at the Harkness Handbook (NARGS).
http://rockgardener.com/harkness/seedlist.cfm?Genus=Sedum
His name on the plant is Sedum roseum.

Here is a link that might be useful: Lili-Ann´s Garden