what is the difference

They are two different species--though closely related. As a group, they along with several other species constitute "angraecoids." These orchids generally come from the African continent or Madagascar. From a technical standpoint, they are different species because they are structurally a bit different. So just as "cattelya" includes a number of different species.

I assume you are asking because there are lots of white flowers from both. Does that answer your question or are you looking for the more technical, taxonomy differences?

 

"They are two different species"

They are two different genera.

 

Aerangis and Angraecum are related, but not closely related. They are similar in appearance and distribution, but they are in different subtribes (Aerangidinae and Angraecinae) in the Vandeae tribe, which makes them roughly comparable to comparing Laelia and Pleurothallis (Laeliinae and Pleurothallidinae subtribes in the Epidendreae tribe). Aerangidinae and Angraecinae subtribes both have many genera and species.

Like many botanical distinctions you may need to dissect a flower and use a magnifying glass to see the technical differences. Aerangis subtribe has an elogated rostellum and Angraecum subtribe has an apron-like rostellum. The rostellum is a part of the column that helps prevent self-pollination. If you are looking for a quick easy visual way to distinguish all Angraecums from all Aerangis, I'm not sure there is one.

In terms of culture, Angraecum tends to grow at lower elevations and in more exposed positions than Aerangis, so Aerangis needs somewhat cooler and shadier conditions than Angaecum in general. But there is certainly overlap so this isn't a universal difference for all species.

 

Thanks Paphman, I enjoyed that explanation. Like so many others, I'm too focussed on the culture of my plants to pay too much attention to my language. It's easy to become a bit sloppy and use terms lightly.

 

Me too apparently. Sheesh -- I do know the difference between genera and species. Thanks for the better explanations.