The semi-vowel v is substituted for the ū of varṣābhū also when a case-affix beginning with a vowel follows.,
As वर्षाभ्वौ, वर्षाभ्वः ॥ वर्षाभू 'what is born in the rains, a kind of herb.' This is an exception to the subsequent rule.
Vart:- The semi-vowel substitution takes place when दृन्, कार and पुनर् precede भू; as दृन्भ्वौ, दृन्भवः, पुनर्भ्वौ, पुनर्भ्वः, कारभ्वौ (काराभ्वौ), कारभ्वः (काराभ्वः) ॥,