る-Verb (Dictionary)

る-Verbs are verbs that have only one possible conjugation pattern. This pattern simply involves the replacement of る with another construction, depending on the tense of the verb (past, negative, etc). This conjugation pattern that only includes る is where the Japanese name Ichidan (一段(いちだん)) 'one-level' comes from.

In these examples, we can see that る is removed from the verb to create the polite ます form. The る form of the verb is often called 'plain form', 'casual form', or 'short form', depending on the source/book.
All る-Verbs end in the kana る, there are no exceptions to this rule.