Early explorers, such as Alexander von Humboldt in 1807, observed a number of notable species in the mountains around Mont Blanc at altitudes above . This was well above the permanent snow line, but on rocks that were so steep that little snow could rest. These arctic-alpine species included: Androsace carnea; Androsace chamaejasme; Arabis caerulea; Cardamine bellidifolia; Draba hirta; Saxifraga androsacea and Silene acaulis (occurring down to ). Between , Humboldt noted the following species of flowering plants amongst rocky debris around permanent snow fields and the highest alpine glaciers: Achillea nana; Achillea atrata; Gentiana nivalis; Juncus trifidus; Ranunculus glacialis; Saxifraga biflora and Saxifraga oppositifolia.