Smilacina racemosa is now called Maianthemum racemosum. Smilacina stellata is now called Maianthemum stellatum.

The Maianthemum gallery (there are 2 pages, be sure to see both) in the USDA plants database has a lot of pictures of both (and other member of the genus). That might help you to recognize some of the differences.

Here is a link that might be useful: Maianthemum gallery on USDA plants database

Hmm, I can't really see any clear differences. I must be missing something! I know I have one of these in my garden, but it seems to have attributes of both. Does it hybridize with itself?

Still looking for a resource for differentiating these two plants...

I have ramosum blooming in my garden right now, I have grown stellata but don't have it now. If I remember correctly my stellata had fewer flowers, the flowers were light and airy, very star like, hence its name and ramosum is a closely packed longer flowerhead. I can't remember if stellata was fragrant but ramosum certainly is. I found this picture of stellata, now I'll see if I can find a decent one of ramosum. Hope this helps.
A......

Here is a link that might be useful: stellata

Here's one of racemosa, I don't know if this will help but if you were growing the two side by side the differences would be quite apparent. Probably didn't help at all, but I tried, forgive my incorrect spelling in my first post, I'ts toooo early in the morning here :o).
A......

Here is a link that might be useful: racemosa

Thanks; that does help some. I also found a source that said racemosa has broader leaves than stellata. Which, as you say, would be easier if they were growing side by side. Sometimes, I find, several observations over flowering time can make it more apparent.

Hi! It's been 17 years but this is the t\op google result for this question. I did some digging and Wilhelm and Rericha's Flora of the Chicago Region notes that (Smilacina) Maianthemum racemosa has subsesille leaf attachments while Maianthemum stellata has sessile leaves. What that means is that there's a little nubbin attaching racemosa's leaves to their stems, meanwhile in stellata, the leaf base almost wraps around the stem.

Comparing the iNaturalist pages helps show this:

https://www.inaturalist.org/taxa/51062-Maianthemum-racemosum/browse_photos

https://www.inaturalist.org/taxa/53268-Maianthemum-stellatum/browse_photos