Perhaps, as the old saying goes....The candle always burns its brightest before it goes out. What you are looking at are it's flowers and for whatever reason it has started to procreate or more likely it is probably the first time you have noticed what has been going on every year for a very long time.

In the forty years this tree has been present, has it never produced copious amounts of seed, that is, the 'helicopters' that go absolutely everywhere?

I'm assuming you're in the UK - sycamore means something different in USA.

I am surrounded by sycamores here. The flowers appear before the seeds (obviously) and are rather attractive - some trees produce whitish ones, and some reddish. I have a love/hate relationship with sycamores. But they're not mine and I have to live with them! The worst thing is the honeydew from the aphids which live in vast numbers in the trees, and which coats the car ?. I had no idea they were a different tree in the US. Please provide more info, Bamboo!

In the USA there are about 5 or six different Sycamore trees but their reproductive modus operandi is for all intents and purposes the same.

Sycamores have spiny, burr-like seed pods, not "helicopters"--those are maples.

Here the sycamore produces bunches of winged seeds which grow almost like bunches of grapes and look very attractive. When they ripen, they fly off, twirling in the wind. Then watch out! Our end of the road is an avenue of sycamores. In spring, my small front lawns are covered with seedlings with a pair of false leaves. The only way to deal with them effectively is just to mow them away.

Tug, to avoid confusion on a UK site, probably best to use 'American sycamore' or 'Maple sycamore' for trees in the USA - sycamore in the UK always means Acer pseuodoplatanus, its not a name ever given to any other tree.

That's why I'm querying whether the tree the question's about is actually sycamore - for it not to produce seed over 40 years is next to impossible - unless its not what we call sycamore!

Oohh!! I see now! In America, we haven't spoken it for years! :D

/with no reply from Annie, we'll never know...

Sorry folks...my sycamore is in the UK and has never produced these catkin like flowers before just occasional aeroplanes but thanks for all the suggestionsame! I'm none the wiser really! Annie

I asked about seeds because, if you've had seeds in previous years, that means it flowered, because without flowering, seed can't be produced. If its got more flowers than usual, then you happen to have noticed them this time, that's all. Expect loads of seeds in autumn!