When one is interested in Citrus, the complexity of the plant group quickly becomes apparent. Check out the names of citrus varieties of the world. - Millet

http://www.corse.inra.fr/sra/synonym.pdf

Millet, thanks!

The Citrus of the world listing has the most number of entries I have come across so far.

The only drawback is that it really doesn't show many synonyms that should have cross referenced each other, and also doesn't show the various local dialect names in many parts of the world.

Here's a reference that does have more comprehensive synonyms but not a lot of citruses:

http://www.plantnames.unimelb.edu.au/Sorting/Citrus_1.html

most plants that either produce nucellar seedings will often fool the taxonomic forefathers leading to a lot of today's naming chaos. It is almost the same with bananas when a zygotic embryo with a different characteristic successfully grows but then it can also reproduce via suckering true to type of the new offspring's DNA. Then add to these the various ploidy levels where whole sets of chromosomes from various parents gets folded into the cells. The definition of what a species should be is lost with these kinds of plants.

Thanks to both for the links. Citrus is indeed complex and the link that Joe provided is an amazing example of that--when you look at the synonyms for Citrus aurantiifolia there are at least 15 variations of the scientific name! Theses are names supplied by various experts in citrus taxonomy! WOW!

Thanks Millet! I really like that link. My husband might find a bunch of paper and printer ink missing...

Here are some other search engines I've used:
USDA
http://plants.usda.gov/java/nameSearch

Zipcode Zoo
http://zipcodezoo.com/