विभाषौषधिवनस्पतिभ्यः

The न of वन , is optionally replaced by ण , when the cause of change occurs in the first member of the compound and which denotes a perennial herb or forest tree.
Karika:-

फली वनस्पतिर्ज्ञेयो वृक्षाः पुष्पफलोपगाः ।
ओषधः फलपाकान्ता लता गुल्माश्च वीरुधः ॥

When the purvapada is a word denoting ओषधि or a perenniel herb, or denoting a वनस्पति or a tree, and it has a change-producing letter, then the न of वन is replaced by ण ॥ This is an optional rule. Thus :- दूर्वावनम् or दूर्वावणम्; मूर्वावणम् or मूर्वावनम् ॥ Here दूर्वा and मूर्वा are names of ओषधि ॥ Similarly शिरीषवनं or शिरीषवणम्; बदरीवणं or बदरीवनं ॥

Vart:- This rule applies when the first word is a dissyllabic or trisyllabic word. Therefore the change does not occur in देवदारुवनम्; भद्रदारुवनम् ॥

Vart:- Prohibition should be stated with regard to the words द्वारका &c. As द्वरिकावनम्, तिमिरकावनम् ॥

Though there is a distinction, botanically speaking, between वृक्ष and a वनस्पति also; yet in this sutra, the word वनस्पति includes वृक्ष also.

Karika:- Technically speaking वनस्पति is a tree that bears fruit apparently without a flower, as a fig tree udumbara. वृक्ष is a tree that bears both flower and fruit, ओषधि is an annual herb, that dies after the ripening of the fruit, and creepers and tubercles are called वीरुधः ॥