In my previous post I ran into a problem with the "global" definition of $directorylist.  If I called the function more than once on the same page it would combine the file lists. I looked at Lasse Dalegaard's example and used the following solution.

remove global definition
     global $directorylist; 

REPLACE 
<?
if ((($maxlevel) == "all") or ($maxlevel > $level)) {
   filelist($startdir . $file . "/", $searchSubdirs, $directoriesonly, $maxlevel, $level + 1);
}
?>
WITH
<?
if ((($maxlevel) == "all") or ($maxlevel > $level)) {
    $list2 = filelist($startdir . $file . "/", $searchSubdirs, $directoriesonly, $maxlevel, $level + 1);
    if(is_array($list2)) {
        $directorylist = array_merge($directorylist, $list2);
    }
}
?>