It means that it should be unable to produce viable seeds. However a good many plants that were assumed/thought to be sterile cultivars have later proved not to be sterile and are able to cross pollinate with similar plants of their species. Not all by any means but enough to keep gardeners on their toes :-)

it means.. it has been bred.. so far out of bounds of reason ... [which is of course what attracts us] ... that it is no longer genetically stable ... and has become sterile .. [or as gal suggests.. it is thought to be sterile]

thats how i think of it ... whether its scientific fact or not ...

but i am not sure if thats what you meant to ask ....

many fancy hybrids.. do not come true from seed ... it doesnt mean they are necessarily sterile... it means you are going to get mom or dad.. not the fancy kiddo ... [and mom and dad.. might be surprisingly ugly .. lol] ... and in this case.. mom or dad.. might be the invasive ....

if you linked us to what you read.. it might be easier to explain ... or maybe not ... lol...

ken

Sigh.....many plant hybrids are sterile, Ken. It's a whole different physiological process than unpredictable the genetic diversity. "Genetically stable" has nothing to do with sterility.

This particular Ruellia variety is said not to produce seed. It does spread via underground rhizomes, however.