I think it is great, a rare one will also offer pups off the sides. Yep, I have seen that. Norma

There was a great discussion on the crested and monstrose forms on another website.

Here is a link that might be useful: crested and monstrose

Thanks, Brad makes some good points on that page. I've also noticed that odd growth tends to occur on older cacti.

So it's not necessarily an expression of traits that were inherited from seed but rather DNA damage that could've been accumulated over the lifetime of the plant.

IE cancer?

I can see some corking adjacent to the edge of that growth, likely the growth point was damaged somewhat and that is why it is doing this. I've heard of 'drilling' out the growth point on E obesa to get them to pup. Similarly I've had grafted plants grow huge without pupping, then when the top is removed to root on it's own (because the stock was unable to support it), the remaining part produces many offsets.

Now I'm envious. None my E. obesa ever lived more than a few months, including the 'William Denton' hybrid pictured below. I guess outdoors in S.D. is simply the wrong habitat. Is that the full flower, or will they open up a bit?
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I've kept all eight of my obesa outdoors for six years now. I got two " clumping " obesa last summer Balboa Park cactus show , they seem to be alittle more fragile but so far they are pulling through . I"ve got a few that appears to become monstrose , they are neat . I got a couple of obesa hybrids from Home Depot last year , I'm not sure what type of hybrids though .
David you should go to SD zoo , they have HUGE obesa outdoors in their african lizard pin , close to the Cyclura pins .

I noticed that too but saw no tip damage last time I had a close look - it usually has to be fairly severe damage to kill the meristem. Interestly, cacti that display monstrose growth also often have that slight corky look in places.

That's a shame David, maybe outside in the ground in zone 10 is pushing it a little, I believe zone 9 is where they originate. Try a pot maybe or more shade? I've found mine tough, like all Euphorbias really. Even a bad case of sunburn, which left nearly a third of it dead, couldn't kill it.

That's the male plant btw. Female flower's different.

Crazy lil pup is flowering already.

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I also have one doing that, it is because I accidently streesed the growth navel. It grows fast because it has the host mother plant feeding it. We have one at the Huntington Gardens with growths coming out of the sides about six of them from memory. Norma

Re: fast growth. Ah yes that makes sense, I think I've seen grafted plants do the same now you mention it.

How does one go about accidentally stessing the growth navel? Sounds like something that may be interesting to do non-accidentally. ;)