My partner works at a botanic gardens and they have to deal with this a lot. For most plants, taking discarded material would be fine, but they have some rare

My partner works at a botanic gardens and they have to deal with this a lot. For most plants, taking discarded material would be fine, but they have some rare plants that are subject to international diplomatic agreements - to paraphrase, "we will give you a specimen of this plant, usually in exchange for some other favour, but only you may grow it". If those get loose, it can spark an incident and potentially cause that international cooperation to cease. These kinds of agreements sometimes happen for countries where previous expeditions have taken commercially valuable crops home and built an industry around them - e.g. the British stealing rubber tree seeds from Brazil in 1876, in order to set up competing plantations in south-east Asia. And of course it's difficult to know which plants are covered by something like that, unless you're very up on your international botanical politics and are extremely good at telling similar species apart.