Lactarius austrorostratus is similar to L. rostratus because the species has similar fruiting body size, color, latex feature, rostrate pleurocystidia and hyphoepithelium. However, L. austrorostratus has larger pleurocystidia and is associated with Castanopsis tree. L. rubrocorrugatus is also similar, but it differs by having reddish cap, transparent latex and smaller pleurocystidia, of which its apex is never rostrate as seen in L. austrorostratus.

The species might have small population size, especially in Thailand. Up to present, the species has been recorded from 3 places, 1 place in Thailand and 2 places in China.

The species is discovered in Northern Thailand. Later, the species is also recorded from China.

The species grows under Castanopsis tree in evergreen forest.

Although the species is found in nature reserve areas, the main threat of the species could be deforestation and the increase in wildfire frequency caused by human activities.

Habitat protection and management are needed.