Icosidesmus montanus is very similar to Icosidesmus variegatus in general features except its colour: it is a rich reddish-brown as are most alpine species. Its habitat is the alpine screes of the central portions of the Main Divide. In the more lateral mountains of Canterbury, Nelson and Marlborough are the very similar Icosidesmus cismontanus , Icosidesmus saxatilis , Icosidesmus orescius, and in South Cnterbury/North Otago is Icosidesmus olivaceus. There are at least two undescribed species lying in the mountains immediately north of those with I. olivaceus.