I had the need to recursive merge the results from a subclass with all of it's parents, and this was the resulting code:

<?php
function GetStaticPropertiesRecursive($class) {
    $currentClass = $class;
    $joinedProperties = array();
    do {
        $reflection = new ReflectionClass($class);
        $staticProperties = $reflection->getStaticProperties();
        foreach ($staticProperties as $name => $value) {
            if (is_array($value)) {
                if (isset($joinedProperties[$name]))
                    $joinedProperties[$name] = array_merge($value, $joinedProperties[$name]);
                else
                    $joinedProperties[$name] = $value;
            } else {
                if (isset($joinedProperties[$name]))
                    $joinedProperties[$name][] = $value;
                else
                    $joinedProperties[$name] = array($value);
            }
        }
    } while ($class = get_parent_class($class));
    return $joinedProperties;
}

Using this function:
class base {
    public static $Test = array("foo1", "foo2");
}
class sub extends base {
    public static $Test = "sub";
}

print_r(GetStaticPropertiesRecursive("sub"));
?>

That outputs:
Array
(
    [Test] => Array
        (
            [0] => foo1
            [1] => foo2
            [2] => sub
        )

)

The merge follows the rules of array_merge on duplicate keys.

getStaticProperties return a set of the property itself. It's diferente from getProperties(ReflectionProperty::IS_STATIC) because it return a set of ReflectionProperty class.