Looking for code for an alphabetic menu in php

With the botanical wood tree that I have been working on, the number of records for genera and for species can get quite large and unwieldy. Presently I have over 6,000 species records that takes a while to load let alone try to browse through. I need to chop this up into querying by alphabet of the first letter of the species botanical names. For the species level of organization, I have been keeping the data in a MySQL file called simply 'species'. I want to have a single character of the alphabet with each acting as a link for the first character of each species name:

        A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
When a user click on one of them, it should be readable (eg. using $_GET??) into a common variable for
them all that can then be used for a select statement. The rest of displaying the

results in columns I already have working fine. What suggestions do you have for typical code that should work? Much thanks in advance, Bill Mudry Mississauga, Ontario, Canada