The Amaryllis Question

Several of my coworkers and I were given planted Amaryllis bulbs last week.  The stalks on each were just beginning to make their way into the world.  The obvious move for us was to agree to race, to see whose Amaryllis grew the fastest.  However, the problem with having several Amaryllis plants in the same office led inevitably to an argument: what is the proper plural form of the word "Amaryllis?"
This seems like a question that a group of employees of Wayside Gardens would know, especially garden writers.  However, with questions about plant names, there often isn’t a single simple answer.  The plant names are often either Anglicized Latin or Greek, or Latinized English.  Also, they are usually created by botanists, who are rarely too concerned with the grammar questions they may be creating.  In the case of the plural for Amaryllis, there are four possibilities that we are considering: Amaryllii, Amaryllides, Amaryllises, and Amaryllis.

Amaryllii seems like it could be right, as many words that end with a similar sound are pluralized that way (Fungus, fungi, etc.).  However, words that are pluralized that way generally end in a "us" rather than "is," so I think that it’s safe to count this one out.  Amaryllides makes use of another form of Greek pluralization, and some botanists do use this.  I haven’t actually met any of these botanists, though, and I really don’t think that this is a very common form of the word (interesting fact, though: the word Amaryllis is Greek, and comes from a common girl’s name in Ancient Greece).  Which brings us to Amaryllises or Amaryllis.  The basic question here is: should the word be changed at all in its plural form?  Amaryllis is a genus name, and the general rule in botany is that the genus name is never pluralized, even when it is being used in the collective.  However, this may be an exception to this rule, because the plants that we’re usually referring to when we say "Amaryllis" are not
actually in the genus Amaryllis, which consists of a single species, Amaryllis belladonna, a South African plant more commonly called "Naked Ladies" or "Belladonna Lilies."  The plants more commonly called Amaryllis in the United States is actually of the genus Hippeastrum (which should definitely not be pluralized).  Thus, I think that it is safe to pluralize the word (unless you’re referring to Naked Ladies), and that we should use the English plural form, Amaryllises (or just always call them "Amaryllis bulbs" or "Amaryllis flowers").  Plus, my spell-checker likes that form better.
As to the Great Amaryllis Race of 2008?  I’m winning.