Isotoma petraea, commonly known as rock isotome,[2] is a small[citation needed], herbaceous plant in the family Campanulaceae occurring in arid regions of Australia.

Isotoma petraea is an erect, spreading, perennial or annual herbaceous plant with smooth branches that typically grows to a height of 0.2 to 0.6 metres (0.7 to 2.0 ft).

[3][4][5] This species was first formally described in 1853 by Ferdinand von Mueller and the description was published in Linnaea: ein Journal für die Botanik in ihrem ganzen Umfange, oder Beiträge zur Pflanzenkunde.

[8] It is found on breakways, among rocky outcrops and in rock crevices in the Mid West, Wheatbelt and Goldfields-Esperance regions of Western Australia where it grows in shallow sandy soils over granite.

In New South Wales it grows west of Wilcannia mostly on slopes and rocky locations on shallow granite based soils.