Volunteer Broccoli?

For the first time ever, we had volunteer broccoli in our garden, YAY!  We transplanted the little guys into a row of their own, and we excited about our jump-start (usually we plant seed thickly, then transplant out from our row, spreading them out).
BUT, they little broccoli plants are not growing as expected.  They are bolting?  The are tiny plants and keep making tiny heads that will go into small clumps of yellow flowers - no "head" to speak of.  We are accustomed to getting one big head, then progressively smaller side-heads into the fall, but these started smaller than the last round of tiny side heads would generally be.  
We thought perhaps they cross-pollinated with something else, but we don't think so.  We had kale, brussels sprouts, cabbage, and kohlrabi in the garden last season, but I do not think that any of those flowered.  We also had lots of arugala nearby, also some turnips that bolted, but I think these are different enough that they do not cross?
Are some varieties of broccoli hybrids, so that they offspring don't resemble the original variety?  My wife thinks that the seed was "Waltham"

Regardless, we are still enjoying the broccoli, it's just not what we expected.  I've been cutting the "heads" with the top few leaves and using that in salads and still-fry.   I would not change our reaction to the volunteers - I do not regret transplanting and nurturing them.

The problem may be that the plants are stressed from being transplanted.

Is your area having an extremely hot summer like we are having in Texas?  That could cause your problem.

Sounds like you have found a solution and are enjoying the volunteer.

Anne Miller wrote:The problem may be that the plants are stressed from being transplanted.

Is your area having an extremely hot summer like we are having in Texas?  That could cause your problem.

Sounds like you have found a solution and are enjoying the volunteer.

I always plant broccoli thick and transplant later.  These were probably the LEAST stressed I have had a broccoli be at transplant, as they were growing in singles and I transplanted them with very little root trauma.
We had a few hot days, but nothing crazy.

Were the parents hybrids or open pollinated broccoli?  Maybe they crossed with another brassica and you have a new kind of broccoli on your hands

If the volunteers came up earlier than the seed you usually plant or if your spring was colder than normal, that could be the problem. It could also just be that the seeds overwintered. Vernalization is a big problem for me with certain crops...actually most of them 🙄

https://www.canr.msu.edu/news/bolting-in-spring-vegetables