diff --git a/core/lib/Drupal/Core/Menu/LocalTaskDefault.php b/core/lib/Drupal/Core/Menu/LocalTaskDefault.php
index 44233e8..603f6b6 100644
--- a/core/lib/Drupal/Core/Menu/LocalTaskDefault.php
+++ b/core/lib/Drupal/Core/Menu/LocalTaskDefault.php
@@ -141,7 +141,7 @@ public function getTitle() {
   public function getWeight() {
     // By default the weight is 0, or -10 for the root tab.
     if (!isset($this->pluginDefinition['weight'])) {
-      if ($this->pluginDefinition['tab_root_id'] == $this->pluginDefinition['id']) {
+      if ($this->pluginDefinition['tab_root'] == $this->pluginDefinition['route_name'] && empty($this->pluginDefinition['tab_parent_id'])) {
         $this->pluginDefinition['weight'] = -10;
       }
       else {
diff --git a/core/lib/Drupal/Core/Menu/LocalTaskManager.php b/core/lib/Drupal/Core/Menu/LocalTaskManager.php
index a02b8bb..013dff7 100644
--- a/core/lib/Drupal/Core/Menu/LocalTaskManager.php
+++ b/core/lib/Drupal/Core/Menu/LocalTaskManager.php
@@ -39,8 +39,8 @@ class LocalTaskManager extends DefaultPluginManager {
     'route_parameters' => array(),
     // The static title for the local task.
     'title' => '',
-    // The plugin ID of the root tab.
-    'tab_root_id' => '',
+    // The route name where the root tab appears.
+    'tab_root' => '',
     // The plugin ID of the parent tab (or NULL for the top-level tab).
     'tab_parent_id' => NULL,
     // The weight of the tab.
@@ -127,6 +127,54 @@ public function processDefinition(&$definition, $plugin_id) {
     if (empty($definition['route_name'])) {
       throw new PluginException(sprintf('Plugin (%s) definition must include "route_name"', $plugin_id));
     }
+    // If the root is not specified assume it's the same as the route.
+    if (empty($definition['tab_root'])) {
+      $definition['tab_root'] = $definition['route_name'];
+    }
+  }
+
+  /**
+   * Finds plugin definitions.
+   *
+   * @return array
+   *   List of definitions to store in cache.
+   */
+  protected function findDefinitions() {
+    $definitions = parent::findDefinitions();
+    // Add root tab in any cases where it is missing.
+    $found_routes = array();
+    foreach ($definitions as $plugin_id => $definition) {
+      $found_routes[$definition['route_name']] = $definition['tab_root'];
+    }
+    $added_tabs = array();
+    foreach ($definitions as $plugin_id => &$definition) {
+      if (!isset($found_routes[$definition['tab_root']])) {
+        // Create the missing tab.
+        $tabs = $this->createMissingTab($definition);
+        foreach ($tabs as $new_definition) {
+          $found_routes[$new_definition['route_name']] = $new_definition['tab_root'];
+        }
+        $added_tabs += $tabs;
+      }
+      else {
+        // If a developer adds a new tab and references an existing tab as
+        // the root, we want to copy that existing tab's root so that the
+        // value is consistent.
+        $definition['tab_root'] = $found_routes[$definition['tab_root']];
+      }
+    }
+    return $definitions + $added_tabs;
+  }
+
+  protected function addMissingTab($definition) {
+    // @todo: Load/validate the route object and get the title.
+    $plugin_id = 'default_local_task:' . $definition['tab_root'];
+    $definitions[$plugin_id] = array(
+      'route_name' => $definition['tab_root'],
+      'title' => 'Default',
+      'weight' => -10,
+    );
+    return $definitions;
   }
 
   /**
@@ -173,7 +221,7 @@ public function getLocalTasksForRoute($route_name) {
         $children = array();
         foreach ($definitions as $plugin_id => $task_info) {
           if ($route_name == $task_info['route_name']) {
-            $tab_root_ids[$task_info['tab_root_id']] = $task_info['tab_root_id'];
+            $tab_root_ids[$task_info['tab_root']] = $task_info['tab_root'];
             // Tabs that link to the current route are viable parents
             // and their parent and children should be visible also.
             // @todo - this only works for 2 levels of tabs.
@@ -188,9 +236,9 @@ public function getLocalTasksForRoute($route_name) {
           // Find all the plugins with the same root and that are at the top
           // level or that have a visible parent.
           foreach ($definitions  as $plugin_id => $task_info) {
-            if (!empty($tab_root_ids[$task_info['tab_root_id']]) && (empty($task_info['tab_parent_id']) || !empty($parents[$task_info['tab_parent_id']]))) {
+            if (!empty($tab_root_ids[$task_info['tab_root']]) && (empty($task_info['tab_parent_id']) || !empty($parents[$task_info['tab_parent_id']]))) {
               // Concat '> ' with root ID for the parent of top-level tabs.
-              $parent = empty($task_info['tab_parent_id']) ? '> ' . $task_info['tab_root_id'] : $task_info['tab_parent_id'];
+              $parent = empty($task_info['tab_parent_id']) ? '> ' . $task_info['tab_root'] : $task_info['tab_parent_id'];
               $children[$parent][$plugin_id] = $task_info;
             }
           }
diff --git a/core/modules/comment/comment.local_tasks.yml b/core/modules/comment/comment.local_tasks.yml
index ee8d3bf..f026671 100644
--- a/core/modules/comment/comment.local_tasks.yml
+++ b/core/modules/comment/comment.local_tasks.yml
@@ -1,15 +1,15 @@
 comment_permalink_tab:
   route_name: comment_permalink
   title: 'View comment'
-  tab_root_id: comment_permalink_tab
+  tab_root: comment_permalink
 comment_edit_page_tab:
   route_name: comment_edit_page
   title: 'Edit'
-  tab_root_id: comment_permalink_tab
+  tab_root: comment_permalink
   weight: 0
 comment_confirm_delete_tab:
   route_name: comment_confirm_delete
   title: 'Delete'
-  tab_root_id: comment_permalink_tab
+  tab_root: comment_permalink
   weight: 10
 
diff --git a/core/modules/system/tests/modules/menu_test/menu_test.local_tasks.yml b/core/modules/system/tests/modules/menu_test/menu_test.local_tasks.yml
index 7d270f3..31c7c54 100644
--- a/core/modules/system/tests/modules/menu_test/menu_test.local_tasks.yml
+++ b/core/modules/system/tests/modules/menu_test/menu_test.local_tasks.yml
@@ -1,54 +1,64 @@
 menu_local_task_test_tasks_view:
   route_name: menu_test.local_task_test_tasks_view
   title: View
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test_tasks_edit:
   route_name: menu_test.local_task_test_tasks_edit
   title: Edit
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test_tasks_settings:
   route_name: menu_test.local_task_test_tasks_settings
   title: Settings
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test_tasks_settings_sub1:
   route_name: menu_test.local_task_test_tasks_settings_sub1
   title: sub1
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
   tab_parent_id: menu_local_task_test_tasks_settings
   class: Drupal\menu_test\Plugin\Menu\LocalTask\TestTasksSettingsSub1
   weight: -10
+
 menu_local_task_test_tasks_settings_sub2:
   route_name: menu_test.local_task_test_tasks_settings_sub2
   title: sub2
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
   tab_parent_id: menu_local_task_test_tasks_settings
+
 menu_local_task_test_tasks_settings_sub3:
   route_name: menu_test.local_task_test_tasks_settings_sub3
   title: sub3
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
   tab_parent_id: menu_local_task_test_tasks_settings
   weight: 20
+
 menu_local_task_test_tasks_settings_derived:
   route_name: menu_test.local_task_test_tasks_settings_derived
   title: derived
-  tab_root_id: menu_local_task_test_tasks_view
+  tab_root: menu_test.local_task_test_tasks_view
   tab_parent_id: menu_local_task_test_tasks_settings
   derivative: Drupal\menu_test\Plugin\Derivative\LocalTaskTest
   weight: 50
+
 menu_local_task_test.placeholder_sub1:
   route_name: menu_test.local_task_test_placeholder_sub1
   title: 'placeholder sub1'
-  tab_root_id: menu_local_task_test_placeholder_sub1
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test_placeholder_sub2:
   route_name: menu_test.local_task_test_placeholder_sub2
   title: 'placeholder sub2'
-  tab_root_id: menu_local_task_test_placeholder_sub1
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test.upcasting_sub1:
   route_name: menu_test.local_task_test_upcasting_sub1
   title: 'upcasting sub1'
-  tab_root_id: menu_local_task_test_upcasting_sub1
+  tab_root: menu_test.local_task_test_tasks_view
+
 menu_local_task_test_upcasting_sub2:
   route_name: menu_test.local_task_test_upcasting_sub2
   title: 'upcasting sub2'
-  tab_root_id: menu_local_task_test_upcasting_sub1
+  tab_root: menu_test.local_task_test_tasks_view
   weight: 10
diff --git a/core/modules/views_ui/views_ui.local_tasks.yml b/core/modules/views_ui/views_ui.local_tasks.yml
index 383ef10..327a33b 100644
--- a/core/modules/views_ui/views_ui.local_tasks.yml
+++ b/core/modules/views_ui/views_ui.local_tasks.yml
@@ -1,22 +1,22 @@
 views_ui_settings_tab:
   route_name: views_ui.settings_basic
   title: Settings
-  tab_root_id: views_ui_list_tab
+  tab_root: views_ui.list
 
 views_ui_settings_basic_tab:
   route_name: views_ui.settings_basic
   title: Basic
-  tab_root_id: views_ui_list_tab
+  tab_root: views_ui.list
   tab_parent_id: views_ui_settings_tab
 
 views_ui_settings_advanced_tab:
   route_name: views_ui.settings_advanced
   title: Advanced
-  tab_root_id: views_ui_list_tab
+  tab_root: views_ui.list
   tab_parent_id: views_ui_settings_tab
   weight: 10
 
 views_ui_list_tab:
   route_name: views_ui.list
   title: List
-  tab_root_id: views_ui_list_tab
+  tab_root: views_ui.list
diff --git a/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php b/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
index 6a7c8af..1969937 100644
--- a/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/LocalTaskDefaultTest.php
@@ -190,15 +190,17 @@ public function providerTestGetWeight() {
       // Ensure that a default tab get a lower weight.
       array(
         array(
-          'tab_root_id' => 'local_task_default',
-          'id' => 'local_task_default'
+          'tab_root' => 'fake_route.default',
+          'route_name' => 'fake_route.default',
+          'id' => 'local_task_default',
         ),
         -10
       ),
       array(
         array(
-          'tab_root_id' => 'local_task_example',
-          'id' => 'local_task_default'
+          'tab_root' => 'fake_route.example',
+          'route_name' => 'fake_route.default',
+          'id' => 'local_task_default',
         ),
         0
       ),
diff --git a/core/tests/Drupal/Tests/Core/Menu/LocalTaskManagerTest.php b/core/tests/Drupal/Tests/Core/Menu/LocalTaskManagerTest.php
index f10bb38..2509d60 100644
--- a/core/tests/Drupal/Tests/Core/Menu/LocalTaskManagerTest.php
+++ b/core/tests/Drupal/Tests/Core/Menu/LocalTaskManagerTest.php
@@ -120,7 +120,7 @@ public function testGetLocalTasksForRouteSingleLevelTitle() {
     $this->setupFactory($mock_plugin);
     $this->setupLocalTaskManager();
 
-    $local_tasks = $this->manager->getLocalTasksForRoute('menu_local_task_test_tasks_view');
+    $local_tasks = $this->manager->getLocalTasksForRoute('menu_test.local_task_test_tasks_view');
 
     $result = array(
       0 => array(
@@ -152,7 +152,7 @@ public function testGetLocalTaskForRouteWithEmptyCache() {
 
     $this->cacheBackend->expects($this->at(0))
       ->method('get')
-      ->with('local_task:en:menu_local_task_test_tasks_view');
+      ->with('local_task:en:menu_test.local_task_test_tasks_view');
 
     $this->cacheBackend->expects($this->at(1))
       ->method('get')
@@ -166,9 +166,9 @@ public function testGetLocalTaskForRouteWithEmptyCache() {
 
     $this->cacheBackend->expects($this->at(3))
       ->method('set')
-      ->with('local_task:en:menu_local_task_test_tasks_view', $expected_set, CacheBackendInterface::CACHE_PERMANENT, array('local_task'));
+      ->with('local_task:en:menu_test.local_task_test_tasks_view', $expected_set, CacheBackendInterface::CACHE_PERMANENT, array('local_task'));
 
-    $local_tasks = $this->manager->getLocalTasksForRoute('menu_local_task_test_tasks_view');
+    $local_tasks = $this->manager->getLocalTasksForRoute('menu_test.local_task_test_tasks_view');
     $this->assertEquals($result, $local_tasks);
   }
 
@@ -188,14 +188,14 @@ public function testGetLocalTaskForRouteWithFilledCache() {
 
     $this->cacheBackend->expects($this->at(0))
       ->method('get')
-      ->with('local_task:en:menu_local_task_test_tasks_view')
+      ->with('local_task:en:menu_test.local_task_test_tasks_view')
       ->will($this->returnValue((object) array('data' => $result)));
 
     $this->cacheBackend->expects($this->never())
       ->method('set');
 
     $result = $this->getLocalTasksForRouteResult($mock_plugin);
-    $local_tasks = $this->manager->getLocalTasksForRoute('menu_local_task_test_tasks_view');
+    $local_tasks = $this->manager->getLocalTasksForRoute('menu_test.local_task_test_tasks_view');
     $this->assertEquals($result, $local_tasks);
   }
 
@@ -267,22 +267,22 @@ protected function getLocalTaskFixtures() {
     $definitions = array();
     $definitions['menu_local_task_test_tasks_settings'] = array(
       'id' => 'menu_local_task_test_tasks_settings',
-      'route_name' => 'menu_local_task_test_tasks_settings',
+      'route_name' => 'menu_test.local_task_test_tasks_settings',
       'title' => 'Settings',
-      'tab_root_id' => 'menu_local_task_test_tasks_view',
+      'tab_root' => 'menu_test.local_task_test_tasks_view',
     );
     $definitions['menu_local_task_test_tasks_edit'] = array(
       'id' => 'menu_local_task_test_tasks_edit',
-      'route_name' => 'menu_local_task_test_tasks_edit',
+      'route_name' => 'menu_test.local_task_test_tasks_edit',
       'title' => 'Settings',
-      'tab_root_id' => 'menu_local_task_test_tasks_view',
+      'tab_root' => 'menu_test.local_task_test_tasks_view',
       'weight' => 20,
     );
     $definitions['menu_local_task_test_tasks_view'] = array(
       'id' => 'menu_local_task_test_tasks_view',
-      'route_name' => 'menu_local_task_test_tasks_view',
+      'route_name' => 'menu_test.local_task_test_tasks_view',
       'title' => 'Settings',
-      'tab_root_id' => 'menu_local_task_test_tasks_view',
+      'tab_root' => 'menu_test.local_task_test_tasks_view',
     );
     // Add the defaults from the LocalTaskManager.
     foreach ($definitions as $id => &$info) {
@@ -291,7 +291,7 @@ protected function getLocalTaskFixtures() {
         'route_name' => '',
         'route_parameters' => array(),
         'title' => '',
-        'tab_root_id' => '',
+        'tab_root' => '',
         'tab_parent_id' => NULL,
         'weight' => 0,
         'options' => array(),
@@ -346,13 +346,13 @@ protected function getLocalTasksForRouteResult($mock_plugin) {
   protected function getLocalTasksCache() {
     return array(
       'tab_root_ids' => array(
-        'menu_local_task_test_tasks_view' => 'menu_local_task_test_tasks_view',
+        'menu_test.local_task_test_tasks_view' => 'menu_test.local_task_test_tasks_view',
       ),
       'parents' => array(
         'menu_local_task_test_tasks_view' => 1,
       ),
       'children' => array(
-        '> menu_local_task_test_tasks_view' => $this->getLocalTaskFixtures(),
+        '> menu_test.local_task_test_tasks_view' => $this->getLocalTaskFixtures(),
       )
     );
   }