Not all of the area above the perennial snowline is permanently snow-covered. Snow accumulates in some places and is cleared rapidly from steep rock by gravity, wind and sun.
In the Mt Cook region there are flowering plants found only on rock above glacier neves. Ranunculus grahamii appears to be restricted to the central alps, but has never been reported west of the main divide. It reaches altitudes of nearly 3,000 metres, along with Parahebe birleyi and Hebe epacridea. Some other vascular plants found high above the snowline include Myosotis suavis, Pachycladon enysii, Poa novae-zelandiae, Colobanthus buchananii, Raoulia youngii and several species of Epilobium. One species of fern, Grammitis poeppigiana, reaches an altitude of at least 2,600 metres – higher than any other New Zealand fern.
One might expect the cushion form to be well represented among flowering plants at the highest altitude, but few are cushions or mats. High-altitude plants live in crannies in solid rock. Such sheltered places are probably where frozen water first becomes available in usable liquid form. Most of the highest altitude cranny plants are relatively soft, herbaceous or sub-shrubby, as in other high mountains of the world.
High altitude plant records
Buttercups are the flowering plant champions of high-altitude growth in New Zealand and elsewhere. In the European Alps the glacier buttercup Ranunculus glacialis grows to about 4,300 metres. The record is shared by Ranunculus lobatus and a scree plant belonging to the mustard family, Ermania himalayensis – both are found at 6,400 metres in the Himalayas.
No ferns or seed plants have been noted above 3,000 metres in New Zealand. Mosses, lichens and algae go higher, just as they extend much closer to the poles than any vascular species. At least 15 species of lichen have been identified from the Summit Rocks area of Aoraki/Mt Cook, at 3,500 metres.
Even the perennial snowfields are far from lifeless. As in other parts of the world, bright reddish-pink flushes on the melting surface of summer snow reveal themselves under the microscope to be millions of one-celled algae (Chlainomonas kolii), swimming for a time in the surface film of water round the ice granules. When the cells enter their resting stage, they mask their green photosynthetic colouring with protective red pigments.