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