I am going to be the second in asking what level are we talking? Undergrad or grad? Advisers guide you in some Masters programs but others leave you to determine your research project. I'm going to go out on a limb and assume you are not a PhD student.
If I may, I would suggest you think about what interests
you. If you are not passionate or at least very interested about your research you are less likely to succeed.
Are you interested in horticultural aspects? Ecological and evnvironmental? Phenotypic plasticity? Epigenetics and genetics? Interactions with other organisms? Local species of orchids or tropical?
Are there any species that interest you in particular?
That said, genetics and epigenetics are pretty hot right now across a wide range of topics. Studies that focus on those areas tend to get funding more easily than say ecology based studies. That shouldn't be your sole determining factor, just something to think about.
I would suggest using your school's journal archives to look at some of the research for the past 5-10 years. Sometimes you can get ideas on research topics doing this. You can also try:
Google Scholar