Answer and Explanation:
Invasive species are not native to an ecosystem/environment to which they've been introduced, which can cause disastrous disruptions to various food chains/webs and other native species' populations.
In this case, your cousin is bringing in a plant from overseas, so it clearly will be an invasive plant. You can tell them the following:
- this plant may take over the feeding source of native plants, causing those populations to decrease drastically or possibly even be wiped out
- secondary consumers that had once relied on those native plants for food energy will now have limited resources, competition will increase, and these consumers may begin to die off
- tertiary consumers that consumed these secondary consumers will begin to die off, as well
- this chain reaction will ripple through the entire food chain and food web, and totally disrupt the existing ecosystem
Thus, your cousin shouldn't plant this organism in their backyard and should instead destroy it.