Using 到底, how could we naturally complete the sentence 虽然这是两棵不同的植物，...? 标准教程HSK4下 (p.79) has a "complete the sentence" exercise:


  虽然这是两棵不同的植物，...。（到底)
  Although these are two different plants, ...


Basically, the task is to complete the sentence using 到底 in a natural way.  (My attempt was a disaster, so there's probably no point in repeating it here; it'll distract more than help.)

Surprisingly, my teacher also seemed to struggle answering this question in a natural way.  The problem is that the sentence talks about plants, and 到底 is used for emphasis.  We thought that only botanists might be passionate enough about plants to use 到底.

Question: Using 到底, how could we naturally complete the sentence 虽然这是两棵不同的植物，...?

I still have no idea.
Try:


  虽然这是两棵不同的植物，但我们到底应该怎样来区分呢？// Though these are two different plants, how on earth should we distinguish them?