This inconspicous, small, corticioid, wood-inhabiting fungus grows on trunks and old branches of living old growth trees of Juniperus phoenicea and Cupressus sempervirens. However, it has only been found at three sites, in a valley in Sardinia, in Tuscany, mainland Italy (where it no longer exists) and in Ibiza, Spain. Although difficult to detect, Arrasia rostrata appears to be very rare despite both tree species being common in the Mediterranean area. The fungus has often been observed in association with the wood-inhabiting tooth fungus Echinodontium ryvardenii growing in the same habitat, which itself has been assessed as Endangered. Although there are only two currently confirmed small areas with fruitbodies known, there is uncertainty about the extent of its true distribution. The total number of mature individuals is estimated not to exceed 250 with fewer than 10 mature individuals present in each subpopulation. A continuing decline is inferred based on the ongoing decline in the number of old trees on which it can grow. Therefore, A. rostrata is assessed as Critically Endangered C2a(i).

This species is only recorded from a few places in Italy and Spain. It was described from the Lanaittu valley on the island Sardinia, Otaly (Bernicchia et al. 2011). A couple of years later it was recorded in the natural cupress forest Cipresseta di Sant'Agnese (Siena, Tuscany, Italy; Bernicchia et al. 2015). In 2018, it was recorded on Ibiza (Sant Joan de Labritja, Aigua Blanca) (Olariaga Ibarguren 2024).

There have been 12-14 observations in one site on two Juniperus phoenicea trees in Sardinia, five or six collections were recorded at one site on a living but not healthy Cupressus sempervirens tree in Tuscany and one collection on bark of J. phoenicea in Ibiza. The Tuscany occurrence no longer exists.

Even though both host tree species are common in the Mediterranean area, although seldom as old growth trees, A. rostrata appears to be very rare even considering the species difficult to detect and identify. It appears to grow in similar habitat as the wood-inhabiting tooth fungus Echinodontium ryvardenii which has been assessed as Endangered (Bernicchia et al. 2019). Presently being known at two sites and from only three trees, with each containing approximately two mature individuals (see Dahlberg and Mueller 2011), this means that the known population size of only six mature individuals. There is a large amount of uncertainty about the extent of its true distribution. Even taking into account potential additional sites that have not been found yet of this extremely rare species, the total population size probably does not exceed 250 mature individuals, with fewer than 10 mature individuals present in each subpopulation. A continuing population decline is inferred based because of the ongoing decline in the number of old trees on which it can grow in the Mediterranean.

Despite the host trees of Arrasia rostrata being common in the Mediterranean area and A. rostrata needing experienced mycologists to detect and identify it, the fungus appears to be very rare. It is an unusual, small, white and soft, corticioid, wood-inhabiting fungus with distinctive large basidiospores developing a characteristic distal refractive rostrum, hence the name "rostrata". The species seems to be associated to the bark of old Juniperus phoenicea and also old Cupressus sempervirens. At the type locality, it has been observed on trunks and old branches of living old J. phoenicea, often growing near to Echinodontium ryvardenii (Bernicchia et al. 2011). It has also been observed as few small spots on a living, but not with a healthy, C. sempervirens in Tuscany, central Italy ((Bernicchia et al. 2015). On Ibiza, it was growing on bark of J. phoenicea (Olariaga Ibarguren 2024).

Being confined to old growth trees of Juniper and Cupressus, its habitat is under threat as such rare trees are often taken down or are harvested and used by people. These are frequently cut for many purposes such as firewood and for making items such as fireplaces and sheepfolds.

The species is not known to be used.

Protection of sites with known occurrences is needed, along with ensuring Juniperus phoenicea and Cupressus sempervirens near to know sites are allowed to age and potentially become appropriate habitat for Arrasia rostrata. Research into its biology and population dynamics will enable more appropriate species management, and searches in potential old growth forests or trees of Juniper and Cupressus is also needed to clarify its distribution in the Mediterranean region.