I'd guess aphid damage during florette formation.

What time of year did you harvest? I grew Cauliflower from a 6 pack, planted at various places in the garden. Some were harvested in early summer and were just great. Others harvested in mid-summer were ugly and unusable. One very neglected plant was harvested just last month and it was superb! I've planted out another 6 pack in places that get only filtered light and easy to keep well-watered. The ones from last year that didn't do well got more hours of sunlight/heat. Hope this helps.

I never saw any aphids on the cauliflower and I do have an aphid spray that I used on the garden anyway. I just harvested that one in the picture today! Feb. 27th. Remember I am in southern California. Cauliflower is listed as a winter crop here. I don't think they got too much heat, though they might have gotten an extra amount of water with the rains we have been having.

Perhaps the original seed wasn't pure strain. It almost looks like you got a cross between a Broccoli-rabe and ?

I had this happen before -- that is not getting the plant as labeled.

In the vegetable forum is a thread "What things have you abandoned and why?" 52 posts quite a few mentioned brasica or cauliflower.
===
snip...No more cauliflower! I tried, it turned brown; I tried again, it got bugs; I tried for the third time and it got bugs then turned brown! Also tieing up the leaves to keep the heads white (ha!) is a pain. For the three or four heads we eat each year, I'll just go to the grocery store.
===
snip...Cauliflower - For the life of me, I cannot grow cauliflower. Spring, fall, whatever! Nice big plants, very healthy, looking great and taking up tons of space. Not even a button! Bah! I've had it...
---
snip...Cauliflower - no luck whatsoever.
---
snip...Yes, it's time to pull the life support plug on both spinach and cauliflower. I've had lousy success with them for four or five years.
---
snip...I am surprised that so many people want to abandon Cauliflower and Broccoli. I am going to grow more of both next year for my market garden. I guess I am just lucky and have the right soil type.
---
snip...Still working out Broccoli, Cauliflower, and Brussels Sprouts. I refuse to give up on them!
---

Here is a link that might be useful: What things have you abandoned and why?

The link for the Cauliflower photo is not working, can you post it again, use the url link thing down at the bottom of the post and copy the url of your photo. I am on Flikr also, I could add you as a contact. I will show an example of a link to a photo on flickr. The link to What things have you abandoned goes to an essay and not the thread.

Here is a link that might be useful: Here are the poppies that I composted last year

Mutant is right. Did they all produce like that?

I've had cauliflower separate from a change in climatic conditions and too much heat but they never looked quite like that. But, I've never allowed it to stay in the ground long enough to see what it would turn into after the florets began separating.

The best cauliflower I've ever had was:

1. When I left the plants to their own devices without giving it too much attention or water.

2. When we received fairly intense cold.

3. When the plants were harvested as soon as they the heads produced a typical circular ball. Allowing them to stay a week beyond this stage always spelled disaster.

And I never covered the heads. Tried it one time and STILL ended up with the florets turning into trees.

I've since given up the idea of growing cauliflower in coastal California. Just a tad too much work for iffy results.

Looks like it was trying to seed to me.