the color of the leaf alone is usually enough. Jubaeas have very deep green leaves that I have never seen on any Butias (relatively pale, blue-grey etc.). Also Jubaea leaves tend to be straighter (arching more with age) and very stiff (Butia leaves are softer and arch, even at a younger age). Jubaeas tend to hold a lot more leaves than a similarly sized Butia (nearly twice as many) making their crowns a lot denser). Butia seedlings tend to have very thin leaflets while those of a Jubaea are nearly twice as wide (this difference fades a bit with age). Also Jubaea leaflets are reduplicate. This means they are folded into a V shape on cross section the entire length of the leaf and the V is pointing down towards the ground (as opposed to the sky or the direction Phoenix leaves point- Induplicate). Butia leaflets are not even folded, or just barely so just at the base where they come off the petioles. I have never had a problem telling these two apart, but Jubaeas can look a LOT like Phoenix canariensis at smaller sizes (leaflet reduplication is a good giveaway there, as are the spiny leaf bases on the Phoenix).

Butia x Jubaeas are much trickier to tell apart as these have variably arched leaves- or sometimes not, can have pale leaflets... or sometimes not, and the leaflets are less obviously folded into a V shape...

I have a few pictures of larger Jubaea and a Jubaea x Butia here.

At 3-5 gallon (if they are nice size), they should show mature leaves.

There are usually pretty distinct charateristics between these palms. I agree with lzrddr, Jubaeas are usually a darker green with fronds that are less arching than Butia, and Jubaeas are less airy looking than young Butias (I guess you can say the fronds are more compact with Jubaeas).
Hybrids are defintiely a lot harder to tell apart!
Some pics would definitely help with the ID!
-Alex

Thanks for your replies posters.

Okay, here's the pic. I did purchase what was advertised as Jubaea chilensis but I also have a few smaller Butia capitatas and am not sure which is which or if I even actually received the correct species ordered. I think this one is the Jubaea or a Jubaea x Butia hybrid. It definitely has a MUCH, MUCH slower growth rate than the ones I know are Butias (and for me, Butias grow really FAST!) I do notice that when the new leaves come out of this one, the leaflets are kind of united together, bend down, then gradually divide.

Here is a link that might be useful:

It looks like Jubaea but I'm not 100% sure. If you want to transplant it, you can look for the seed. The Jubaea seed is much larger than Butia.

Where did you buy it?

I purchased on eBay last year. Do you think it needs transplanting? I usually transplant in spring if necessary.

Definitely does not look like a butia to me. If anything maybe its a hybird of a Butia and a Jubaea, but it seems to have at least some Jubaea in it to me!

-Alex

Thanks Alex, I appreciate your opinion. Really do not need another Butia so was hoping it was at least part Jubaea--time will tell how much Jubaea it has in it. Geez, Jubaeas are this slow growing?! If this IS a hybrid pure Jubaeas must be even slower--assuming the hybrid grows faster. (I know Butias can have a slow-growing reputation, but I think they must be the fastest growing ones for me as they seem to go from one gallons to super-sized containers faster than any other palm I have!) Now I gotta check to see pics of mature hybrids--hope they have half the trunk of pure Jubaeas! Happy New Year!

mY only Butia x Jubaea grows WAY slower than either pure species by the way.

Seems pretty anemic for a Jubaea... pale leaves and too long (grown in shade?). Of course you may not have the luxury of growing young palms in full sun year round, but Jubaeas like a LOT of sun at that age (unless it's over 100F). Might give it a tad bit of liquid fertilizer during warmer weather, too. In it current condition it looks like it has a lot of Butia in it to me.

It doesn't need to be transplanted but it will give you a definite ID.

Pretty much had full sun for most of the year although a few days did exceed 105 F.. I think it may be a Mg. deficiency so may feed with and give some Epson salts. I have one other palm that shows some yellowing--the Paroutis, and read this was a Mg. deficiency that they are prone to. Some sources say that the hybrid Jubaea x Butia is faster growing (which would seem logical), but this one is not fast at all compared to any of the Butias. I agree though, does not look like the Jubaea pics I see on line at all--leaves seem more rigid on the Jubaea. Really would like a pure Jubaea so may attempt to acquire another eventually. Assuming they are extremely SLOW from seed. Are they? More mature specimens tend to be sooo expensive. Thanks again for all your opinions.

Have a few I have grown from seed and yes they are slow, though Butias are initially slow, too. I still have one from a seed I tossed out thinking it was no good... germinated and grew in the ground 3 years ago and still only have thin, strap leaves. Seed germinated over 2 years after I got rid of it.

the trunk definitely looks like a jubaea but the leafs dont. more like butia but not totally sure. still a nice palm & time may tell you more! GL

Heres a pic of mine, trunk looks similar to yours!