my @tree_array;
# my @species = split "//", $list; 
# would:
#   foreach my species ('a','b','c') {} work? I think not?
foreach my $species(@species)
{
     my @tree = edit($species);
     push @tree_array, [@tree] if @tree;
     print @tree if @tree;
}

## do you want to use @tree here?
## if so, then ...you need to use the array
## of the @tree results...

foreach $tree_ref (@tree_array)
{
    print "@$tree_ref\n";
}

sub edit
{
    my ($species) = shift;  #slightly faster when just one arg
    
    my ($pid) = ($species =~ /RANK.*?subspecies.*?PARENT ID.*?(\d+)/);
    ### or ###
    ## look for "PARENT ID", then anything until there are
    ## one or more digits
    my ($pid) = ($species =~ /PARENT ID.*?(\d+)/); 
    
    if (defined $pid)
    {
        return `getz "[taxonomy:$pid]" -e`;
    }
    return undef;
}