As far as I know the Ipomoea indica does not produce seeds in Spain, but is considered as an invasive weed and grows everywhere and I wonder how does this plant do it?
Plants may have multiple methods of reproduction (sexual and asexual) like clones in the form of bublets, stolens, rhizomes.
I found this on the web.
Seeds are rarely produced, but as the vine grows very rapidly, often sending runners along the ground to new areas (unknown to the causal observer), it is often thought to be 'self-seeding'. Can cover large areas in a short time! Ipomoea indica can be invasive and should not be planted close to wildlands!.
In Fethiye, Turkey Ipomoea indica is widely grown in gardens. Prunings, if kept damp in a heap of garden rubbish, will easily root down. Also rooted stems are probably passed round gardeners, since it has attractive flowers and is easily grown. I would surmise that most of the spread is by humans. I have not seen any seed produced.
Could the plant be a sterile hybrid because it is very strong growing?
I am currently living in Spain and I can tell you that it produces seeds. It spreads by runners but also by seeds. I have seen it in many place all along the Mediterranean coast.