The 'primula' word has been much abused in horticulture for several hundreds of years. Technically Primula is a genus of plants with many different species including our own primrose and cowslip and the Himalayan candelabra primulas that some of us grow.
In your question I suspect that you are talking about the multicoloured polyanthus and primulas that you find in garden centres. There are two basic forms of these plants and the names used seem to vary between sellers. My own interpretation is that a Polyanthus has a tall stem with the flowers at the top of it whilst a Primula will have it's flowers low down amongst the leaves in the manner of the primrose. I am quite sure that some GoYers will agree with this and others disagree.

I agree with you Bb, primula being the genus and such as primroses pastel and short with polyanthus taller and brighter

Thank you,Bulbaholic,that is very helpful..the ones I saw at the garden centre yesterday,all looked the same ,and as they were side by side,I couldn't see any difference..so now I know what to look for...but I suppose either will be fine for a bit of winter colour in pots..I was just curious..:o)
Thank you also,Pam....all I have to decide now,is what colours to choose ..:o)

Thats a good question, I have myself always wondered about the difference.

Glad I wasn't the only one Lincslass..:o)

my primulas self seed very easily and look lovely across the lawn-- being so low to the ground mowing doesn't affect them at all

I'd something ticking my memory so I looked it up, there are two different centres for primroses pin eyed and thrum eyed-- pineyed looks like a slightly green pinhead and thrumeyed a cluster of yellow stamen----fascinating!

That is interesting,Pam.I will take notice of them ,as I haven't heard of those names before ...I only have some of the Primula Denticulata's ,which also seed,and I also split them. Do Polyanthus seed as well?

I always think they revert as well Bloomer, I place them in my raised bed and after a few years they all end up red with the tall stems or yellow like the natural ones in our woodlands, I still like them though.

Denticulatas are smashing, my daughter has loads of primroses in her lawn Pam, they were there when she moved in,looked a treat last springtime...

Something else I didn't know,Lincslass..I always thought they stayed the same colour..but red or yellow would be nice anyway..:o)

I did a blog about pin and thrums in Nov 2009 called On closer inspection. I love the morphology of this genus.

I will take a look at that,Sbg..thanks..

Easy to remember the difference for the spring bedding ones because poly means many and anthus means flower, so the polyanthus has lots of flowers on one stem while the primrose has just one. They are all primulas as Bulbaholic says, and many other different primulas such as denticulata and auricula also have lots of flowers on one stem.

I think the confusing use of the name primula rather than primrose for the low growing ones is probably left over from the time before there were all these modern varieties, and usually applied to some rather sad pale purply ones that used to be very common in gardens.

I found your blog ,Sbg..very interesting.,and good reading....comical too,loved all the comments.:o)Thank you ..I will be like you,and peering into the centres of them ..

Thank you also,Steragram,,another good tip for me..I remember the sickly looking purply ones ! It's amazing how much I have learned from my question..thank you everyone ...I am very tempted to be wicked,and ask if they have any Pin or Thrum eyed ,at our garden centre..and see if they impressed by my new found knowledge.:o)

:)))

I like the very pastel ones in the lawn, they look'right' somehow,