As others have said, if you are living in the US it's very unlikely that's a Banisteriopsis. It could be a Wisteria species, very common in gardening and with similar leaves. Unless your neighbors were ethno-pioneers a couple decades ago and somehow imported a cutting or seeds, that sounds more realistic.
The easier positive ID would require checking the flowers, come the season. Of course you could try to get it analyzed or to perform analysis yourself if you have the means, but unless the neighbors are the spooky kind, why not go and ask? I understand if you don't feel like ringing their bell and asking if they have Caapi vine growing in their garden (wink, wink) but wondering if that's Wisteria because you wanted to grow a bit for the beautiful purple flowers, and politely asking them if you can take a solid cutting, might save you a lot of hassle.
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Topic: possible banisteriopsis like species? (Read 16347 times)