//最下層のカテゴリを取得
function get_term_descendants ( $post_id, $tax_name) {
$terms = get_the_terms( $post_id, $tax_name );
if ( empty( $terms )) return false;
$candidate = $terms;
$count = count( $terms );
if ( $count > 1 ):
foreach( $terms as $key => $term ):
foreach( $terms as $term2 ):
if ( term_is_ancestor_of( $term->term_id, $term2->term_id, $tax_name ) ) {
unset( $candidate[$key] );
break;
}
endforeach;
endforeach;
endif;
return $candidate;
}