At least 67 distinct algal taxa occur in the alpine basins of Mt Philistine, Arthur's Pass National Park This flora differs from others reported in alpine and polar regions. Nine species of snow algae were found, none of which appear to grow in other habitats, and at least 6 of which are new records for New Zealand. An abundance of other algae are present, including cf. Gloeocapsa, Cyanothece aeruginosa, Fischerella sp., and Myrmecia cf. irreguiaris, which are particularly widely distributed throughout different habitats on the site. Certain other taxa are common in selected habitats, such as cf. Ammatoidea in some pools and Chlainomonas kolii in snow on the surface of an alpine tarn. Distinct assemblages of algae occur in snow and associated with the moss Andreaea mutabilis. Assemblages in pools, soils, mineral fines, on rock surfaces, and associated with vascular plants are not distinguishable, which may reflect the shortcomings of using presence/absence data as the basis for ordinations. The complete life-cycle of the enigmatic C. kolii is still not understood. This alga has previously been found only in snow beneath forest in North America, where it is generally exposed to much lower light intensity and higher nutrient levels than in alpine New Zealand. However, C. kolii on Mt Philistine grows during prolonged rainstorms, when liquid water content increases, light intensity decreases and freezing at night is absent. Timing of the bloom each year appears to be related to the amount of snow deposited during the previous winter. Snow algae resting cysts are deposited by retreating snow onto underlying substrata on the site. However, their ultimate fate is unknown. Many algae are lofted and dispersed elsewhere, including onto snow from other habitats. An unidentified snow algal cyst (possibly Chlamydomonas sp.) is a small component of the aerobiota. C. kolii has not been found in these samples. The cyanophytes Fischerella sp. and cf. Gloeocapsa dominate the aerobiota. Collection of air-borne algae illustrates the problem of distinguishing wind-deposited propagules from active algae in a given habitat, especially those organisms requiring cultures for their detection and identification. Temporal variation of cultured organisms from aerobiota suggests that their growth periods are distinct from many of those absent from cultures. This is a further factor reducing the resolution of ordination techniques for analysis of distribution patterns.