Thank you for contacting us.
When LDAP is configured and the provider enabled, you will get a dropdown with the available providers:http://screencast.com/t/ouZ3uDsK8wt
In your project, it is possible that the default provider has been disabled and you can use only the LDAP. You can check this in the Security.config file found in the App_Data/Sitefinity/Configurations folder. If the Default provider has been disabled, the node will look like this: