First, I doubt that there are any truly "sterile" maples :-) While seeds (the 'spinners' or samaras) are sometimes not produced until the tree reaches a degree of maturity and maybe not even consistently after that point, it will produce seeds. They are just unlikely to be true to the parent tree unless it too is seedling grown. Even the hybrid Freeman maples, reputed as being sterile, have been shown to produce viable seeds. To be accurate, sometimes the seeds produced will not be viable or produce only male flowers (and therefore no seed) but they can and do cross pollinate with other cultivars of Freeman maple.

So fwiw, some plants that are reported or thought to be sterile are not. Or prove not be over the course of time. That is the case with the purple loosestrife - the so-called sterile forms cross pollinate freely with the native weed species (Lythrium salicaria) and will then produce viable seeds and contribute to the invasive issue. This is a similar issue to the Bradford pear, originally thought to be a sterile cultivar but which now hybridizes freely with other pear species and with any other callery pear.

Some hybrids are indeed sterile and are highly unlikely to produce viable seeds. But I'd be very leery of any non-hybrid cultivar touted to be sterile. I'm not convinced that the new "sterile" forms of butterfly bush are indeed sterile........they have just not been on the market long enough or widely grown enough to fully confirm that attribute. And that they can't cross pollinate with other, non-sterile forms to contribute to the invasiveness problems with this plant.

this year it is producing spinners

==>>> but that doesnt mean ... there is viable seed in it ...

e.g. there are hosta ... that flower.. and set pods .. but there is nothing in them ... the seed itself.. never matures ... so they are called sterile ...

so all you are left with .... is planting a few of them in a pot.. and seeing if anything happens.. though i am sure.. scientists with tools could find out other ways ... [or even the wet napkin trick] ...

ken

ps: of course.. with some maples.. you could just throw them in your gutters.. and grow some trees at height.. lol ...

Re purple loosestrife cultivars: the problem is apparently both cross-fertilization with the species or other cultivars but also the loss of plant self-incompatability.

Nepeta is another case where there exist sterile hybrids which can cross pollinate with other Nepeta cultivars/ species.

my guess with the "sterile" maple tree is following scenario

the person bought a young plant at a nursery and after 10 years it matured enough to flower, the baby grew up and went through puberty... ;-)

and it probably cross pollinated so it could set seeds.

and I like Ken's suggestion to test the seeds

very similar thing happens with Ginkgos which undergo a miracle-sex change.... a Ginkgo grows for 10-20 years and never sets fruits, so "it is a male"..,

until it matured enough to flower and produce fruit in which case ingorant watchers missinterpreted events and did not take into consideration how slowly tree species develop or mature...

Thanks, all!