Any idea which houseplant this broken-off bit is from? And would it root?
Thanks!

I'm not certain but I think that lovely plant is a variety of Anthuriums (Anthurium) and it does appear as if there is a bit of woody base there towards the bottom of the stem, so I'd think it would produce roots. Give it an airy potting media, with lots of added perlite or orchid bark, or leca mixed in. Place it in a warm location with bright light but no direct sun. It looks to be possibly in the Flamingo Flower (Anthurium andraeanum) group but as I said, I'm not really sure.

Member @Gina1960 may be able to help with an ID.

Many thanks! I'm no great houseplant expert. Yes, it looks to me as if it should root.

Agree, its an Anthurium andreanum. PLEASE take it out of the water and follow Lin's advice on the potting up...it already looks like it HAS maybe one root (those brown things papery things sticking up are old cataphylls --leaf sheaths--and you can gently pull those off if you wish but I think I see one root as well) and will make more.