[slow_worm]

The RHS help and advice thing says it word for word and you have listed the main gardening crops that come under that label.Are you wondering how to fit them into a rotation in a sensible 3-4 yr kind if way?Or is making a rotation plan giving you a headache?Put them in newly manured soil and the roots will fork,stones obstructing growth also cause forking.We have clay soil and are adding gritty sand and compost before we plant and this will gradually mean that all the beds will have better soil eventually.In some rotation plans you`ll just find them lumped in as root crops.Don`t know if this helps.

  Thanks Annie. People think I am a pain, wanting to complicate things - but I have the sort of mind that needs to see how things fit into categories. You saw my problem and have explained things very well  
These "Umbellifers" I now see, are the group of root vegetables that need soft soil for the roots to go straight down ....... is that it?

Just one more thing Annie - Do they all have the same NPK requirements and is that mainly potash for the roots?

Jim

Hey why not talk about 'Cruciferous' plants, the cabbages, etc!! Again these are classified due to their flowers too!
Here's a bit of botany...
cabbages, sprouts , caulis all modified forms really of the same base plant.  Large buds (sprouts) selected for in one form and heavy florets (curds) in your caulis, and again thick stems in the KohL rabi!  Essentially they are all same basic plant!!  This is why they are all suseptible to same pests and diseases.

[Annie]

I didn`t mention the Cruciferae family because no one asked and it`s no good complicating things.For anyone who feels a burning need to know as well as the brassicas the other crucifers include swedes,turnips,radishes,khol rabi,rocket,land cress,mustard,stocks........
So there you are slow worm,rotate.