Field populations of Oscillatoriales, from fresh and saline lakes and ponds, and from terrestrial habitats, are characterised on the basis of their morphology and morphometry. Fifteen morphotypes are recognized principally from the following characteristics; cross-sectional shape of the trichome, presence or absence of a calyptra on the apical cell, occurrence or otherwise of numerous trichomes within a common sheath, and trichome width distribution. Where possible morphotypes are assigned to traditional species described by earlier investigations of algae in the Ross Sea region and a reassessment is made of the early descriptions, in some cases using material from the identical locations to the original collections. The following traditional species are described; Lyngbya murrayi, Microcoleus vaginatus, Oscillatoria deflexa, O. koettlitzi, O. priestleyi, O. sancta, Phormidium autumnale and P. subproboscidea. Intraspecific morphotypes of M. vaginatus, O. priestleyi and P. autumnale are recognised on the basis of trichome width. A new species and variety of Crinalium (Crow) Winder, Stal & Mur, a genus characterized by flattened trichomes, are described from cryoconite ponds on glaciers. C. glaciale sp. nov. possesses wide, straight trichomes in contrast to C. glaciale var. helicoides nov. var. in which trichomes are narrower and helically coiled.

Temperatures within soil and plant habitats on Signy Island in the maritime Antarctic were measured during 1987. Four sites were monitored using minithermistors attached to a data logging system. Three main periods within the annual temperature cycle were identified. In spring/summer (November–March) there was much inter-day variation in maximum temperatures, but minimum daily temperatures were always close to 0°C. However, there were very few freeze-thaw cycles extending below the −0.5°C threshold during this period, and those that occurred were not severe. It is considered that freeze-thaw cycling is unlikely to be a significant factor in organism survival during summer. All sites showed a long period of relatively mild subzero temperatures during autumn (March–May). This may be of importance in promoting cold-hardiness of organisms living in these ecosystems before the decline to lower winter temperatures. Minimum winter temperatures varied markedly between sites; lowest temperatures occurring in areas where there was little insulating snow cover. Within site temperature variation was generally small, confirming the validity of the use of small numbers of probes to monitor environmental temperatures in such habitats.