I'm trying to ID a white azalea I have, and thought it might be Pleasant White, and noted there is also a Girard's Pleasant White which the Missouri Botanical Garden states is a synonym. I have a hard time navigating the Catalog of Life, so can't confirm if these are the same plant or not.

Azalea (Rhododendron 'Pleasant White')
Azalea (Rhododendron 'Girard's Pleasant White')

The CoL doesn't list cultivar names so you wouldn't find either of them listed there. MOBOT states 'Pleasant White' is a Girard hybrid and other nurseries list it that way too so I'd say they are one and the same plant and should be merged.
http://www.missouribotanicalga...
http://www.rarefindnursery.com...
https://www.rhododendrons.co.u...

I didn't realize the CoL did not include cultivars...which may well by why I can never find anything on that site! Duh... So, what web site is best to use for reliably accurate information? I hesitate to fully trust nursery sites. I will often use university sites, but they are often more focused on their specific regions. I've had good luck with the Missouri Botanical Garden site but they don't always have precisely what I am looking for. The USDA site is for plants native to or naturalized in north America. Just hunt and peck?

If the CoL lists plant cultivar names, I am not aware of it but maybe they do ... hopefully one of the DB moderators who are more familiar with stuff like that will be along soon to confirm.

MOBOT is one site that I trust but when it comes to cultivars, I really have no idea; I just hunt and peck and try to find consistency.

I was told that the CAT does not list cultivars. I kept trying to find them, unsuccessfully.

Bonehead said:So, what web site is best to use for reliably accurate information?

Since there is no single source for reliable information it's necessary to approach cultivars differently than species plants. There are international cultivar registration authorities (ICRA) for some but not all genera. ICRA maintain registries of cultivar names but not all are online or viewable without joining a society. Two good general websites to visit are the Missouri Botanical Garden and the Royal Horticultural Society databases. The RHS is the ICRA for quite a few genera. Here are some bullet points which might help.

International Society for Horticultural Science list of ICRA, alphabetical by genus. A website to a society is often shown.

A few general go to sites:
Missouri Botanical Garden , Royal Horticultural Society, KAVB (for bulbs).

A few ICRA and good helpful sites (mostly to illustrate how you may need to search):
ICRA for Hosta - American Hosta Society registry
Helpful site - Hosta Library

ICRA for conifers - RHS Conifer register
Helpful site - RHS Encyclopedia of Conifers, American Conifer Society ConiferBase,

Always feel free to look for information in this forum and one of our members will try to help.

Thanks Evan. Good info to know. I've added the Missouri Garden and RHS to my links so I can quickly access them.