Over the years we've used quite a number of different sources to find names of plants while working on the wiki. The one I like at the moment is The Plant List. It's a compilation of a lot of data bases. Type in a genus and search for information. They list with stars how reliable the rating is and give you links to other data bases to check what others think. http://www.theplantlist.org/ It lists 278 names for Hippeastrum, including synonyms and unresolved species. I used it recently to look up the spelling of Pasithea caerulea. It looks like most of the data bases are spelling it this way, although Tropicos spells it Pasithea coerulea. For South African bulbs I look at the references from the South African Biodiversity Institute's online checklist. http://posa.sanbi.org/searchspp.php