(PHP 5)
ReflectionParameter::getDeclaringClass — Gets declaring class
Gets the declaring class.
This function is currently not documented; only its argument list is available.
This function has no parameters.
A ReflectionClass object.
Example #1 Getting the class that declared the method
<?php
class Foo
{
    public function bar(\DateTime $datetime)
    {
    }
}
class Baz extends Foo
{
}
$param = new \ReflectionParameter(['Baz', 'bar'], 0); 
var_dump($param->getDeclaringClass());
The above example will output:
object(ReflectionClass)#2 (1) {
  ["name"]=>
  string(3) "Foo"
}