Ditch weed is a generic term from the USA for naturalised escapes from farmed hemp, it can be tall or short dependent on the variety ie:- from seed production or fibre or dual purpose. It is high CBD low thc. All are Cannabis sativa hemp.
For hundreds of years wild hemp used to grow all over the south of England, to just north of the wash on the east side, but it never auto flowered and the wild hemp was indistinguishable from the cultivated hemp. In other words it was acclimated/adapted to our climate and seasonal variations.
Cannabis Sativa Ruderalis was classified in the nineteen twenties, it is a specific wild sub species from Russia and Siberia, with very high CBD very low thc. Depending on the area it comes from, pure Ruderalis flowers at 3 to 7 weeks from germination irrespective of daylight hours, tends to have single stem and single leaf blades and only grows 4 to 24 inches tall at maturity.
Ruderalis has been bred with with hemp in Russia so seed and fibre crops could be reliably produced north of 55 deg latitudes. Lots of recurrent selection has been done over many years, these lines are not Ruderalis but stabilised inbred selected lines that carry the auto flowering gene from Ruderalis.
In Canada and the USA they often misquote acclimated cultivated hemp escapes as Ruderalis, its not, ditch weed almost never has the auto flowering gene in the USA, if it did it would be a hybrid. Nowadays sometimes in Ca wild stands of hemp have the auto flowering gene, probably because of cross pollination with ruderalis hybrid drug cannabis varieties grown by gorilla growers or from farmers growing Russian derived seed production strains. This still does not make these plants ruderalis, none of them are, they are hybrids containing the auto flowering gene.
As far as I know ruderalis has never been used by western hemp breeders to cross with seed or fibre hemp strains as most hemp is grown well south of the 55 line and varieties that respond to the natural daylight pattern are much much more productive making full use of the season to grow and fruit..
Neville was the first to produce hybrid seed products for sale by crossing Ruderalis or a Ruderalis hybrid with drug strains. He made crosses with both drug quality Cannabis Sativa and Cannabis Sativa var Indica. I suspect he did not use pure Ruderalis but a hemp x R hybrid.
A couple of the original lines he made are still available today from the Sensi seed bank. As Ruderalis Skunk and Ruderalis Indica.
Sagarmatha have a stabilised autofloweing variety called Stuporsonic, they are out of stock, new seed expected 05.
Much more work has been done in Canada probably the best product to date is Mighty Mite and its hybrids.
One thing is for sure once you have the auto flowering gene in a breeding line its impossible to eradicate.
There is some interesting reading
here even if I tend to disagree with some of what they say, have a read and make your own mind up.