The Celandine Major leaf resembles a maple leaf; its lobes join together like a hand with a palm. Celandine minor, on the other hand (pun-ishment, sorry) has lobes that are dissected from the palm. (Did I describe that sensibly?) Not every single leaf stem is identical so, when in doubt, look at the other leaf stems in the clump.
(The clumps are very easy to remove by hand or with pointed thin tool, because they have a central 'carrot-like' root.) Take a look at these photos to see how the leaves are different.

celandine major- the treasure

From 4 28 11

clump of weed celandine minor

From 4 28 11

comparing two celandines
c.major(treasure) on L and upper; c. minor(weed) on bottom and R

From 4 28 11

It's interesting as C. major slowly seeds and at least in my garden after a couple of seasons becomes a huge mound whereas minor really replicates quickly and is not quite so large. That's another way I tell the difference.

Thanks for the pictures - this one is really tough to ID I almost go on instinct as to yank or not to yank in yards.

Ranunculus ficaria is also a very weedy, rather invasive species but one I rather like. I certainly wouldn't recommend planting anywhere near a natural or woodsy area but in a cultivated woodland garden (with no chance of escape) it makes a bright spring showing before disappearing completely in summer.......a true spring ephemeral! I planted a few of the bronze leaved forms ('Brazen Hussy' - gotta love that name!) in my old woodland garden and they spread nicely but manageably. They did spawn some plain green-leaved offspring which seem to be much more aggressive and those I removed.

Now my weedy poppy relative is Meconopsis cambrica or Welsh poppy - an enormous pest that is terrifically difficult to get rid of because a) it self-seeds like a banshee and b) has a deep and persistant taproot.

Chelidonium majus DOES go by the common name of greater celandine (less commonly, celandine 'major'.) and is surely the plant in your pics. However it is a monotypic genus (only a single species) so I dunno about celandine 'minor'.....maybe just a weedier, seedier variant? If I were ID'ing, I'd say the second (celandine minor) was probably Stylophorum diphyllum, aka celandine poppy. IME, both are equally weedy :-) btw, just to confuse the issue further, greater celandine is also a common name applied to bloodroot, Sanguinaria.

But I do not know of any plant other than Ranunculus ficaria that is commonly referred to as "lesser celandine" :-)

Oh, those darn common names!! They get ya every time!

Sometimes, with all the confusion of the common names (the Baneberrys, Cohoshes & Snakeroots come to mind as a real pain to keep straight especially since they reclassified Cimicifuga racemosa to Actaea and Snakeroot can refer to either those in Rununculus or Aster family) I like to refer back to the family name the plants originate from then it clears up many of the identification issues. Good for indentifying what pests, diseases they are prone to as well. As in this case, Rununculaceae & Papaveraceae as GG pointed out solves which celandine belongs to where.

Marie

Now let me get this straight. You two botany savants are actually telling me that these two plants, that have leaves THAT I CAN HARDLY TELL APART, that have near identical flowers as well, that these two plants are actually NOT in the same GENUS?? that one is a poppy and one is a buttercup???? I am scraping my disadvantaged brain to find any similar case in the world of perennials. I mean, the 4" tall weed of japanese knotweed... is in the same genus as the much taller-larger form of polygonum bistorta superbum. IN THE SAME GENUS!!

Why do i have the strange sensation that you two are going to come up with a number of other perennial examples of like situations(i.e. near identical form but different genus)?

Or is this likely to, some time in the future, follow the course of the polygonum/persicaria/falopia re-categorizing??(I figure every expert field has their To Do list, right?)

I await, somewhat sleepily, your answers!!
best,
mindy
(note how, when i�m embarrassed, i never put the website link!)

And of course the ranunculus is a different beast altogther but with the common name of celandine applied, just added to your (and my!) confusion.

and i also see that their seedpods are completely different. long and skinny for the weedy Chelidonium and round and hairy for the treasure Stylophorum.

http://en.wikipedia.org/wiki/Stylophorum_diphyllum

http://en.wikipedia.org/wiki/Celandine

and the treasure is Stylophorum or Celandine Poppy
and the weed is Chelidonium or Greater Celandine.

"My brain is full. can i go home now?"(gary larsen)

gg, the Ranunculus ficaria, or Lesser Celandine>> it has really spread this year- all over beds. it disappears in summer but does it Choke and Vanquish before that, so i should be weeding it out? thanks much.

mindy