105 



IV. P elargonium-M csemhryanthemiim-P oa community. 



This is the earhest phase noticeable in the colonization of granite rubble in 

 shallow pockets in the rock on all the islands. The community is composed of 

 Pelargoniuni australe, Mesembryanthemum aequilaterale, and Poa caespitosa, 

 V. Billardieri. 



The pelargonium is low growing with succulent half-shrubby stems. The 

 plant has a stouter habit of growth than it has when growing on sand dunes on 

 the mainland. Mesembryanthemum aequilaterale is another dune plant which 

 on Pearson Island has a less spreading mat habit than is usual. Poa caespitosa, 

 V. Billardieri, has wiry, pungent-pointed leaves, and the short straw-coloured 

 panicles typical of the variety. These plants appear in exposed, barren soil at 

 all levels. Thus, at the summit of 781 Hill the Mesembryanthemum. and Poa 

 are growing along the exposed precipitous western face. They also occur on 

 the bare patches of coarse sand in the upper part of Main Creek. There the 

 soil (Sample 4) is poor and deficient in soluble salts. Transitions between this 

 community and the Olearia-Lencopogon thicket are common. The shrub appear- 

 ing first is Olearia ramiilosa; Rhagodia baccata less commonly. The annual 

 Lepidium foliosum, too, is often found, as is the cushion plant Scleranthus 

 pun gens. 



Communities on the Granite Cliffs. 



Exposed, precipitous, granite clilTs occur on most parts of the islands. The 

 type of vegetation they bear is largely a depauperate form of the neighbouring 

 less exposed faces, but it seems permissible to refer to cliff floras. Naturally, an 

 important factor influencing these is the degree of exposure to salt spray. 



In the most exposed places the cliffs, or platforms, of rock that rise at an 

 angle of 30° to 45° from the sea are entirely bare for 100 to 150 feet above 

 tide marks. In rubble pockets above this height occur such plants as Mesem,- 

 bryanthemiim australe, Salicornia australis, and Sueda austraUs. These all 

 grow stunted in small mats. The habitat is not suitable for most flowering 

 plants, and even lichens and algae are absent. The relatively rapid weathering 

 of the rock faces may account for this, as well as exposure to heat, wind, and 

 spray. The surface of the granite in these places is either smooth where 

 exposure is most severe, or crumbly and flaky to the touch owing to rapid 

 weathering. Below such places is a conspicuous layer of coarse barren debris. 



Other cliff plants are really chasmophytes growing in deep cracks between 

 the boulders. In such places occur, in addition to the above, Calocephalus 

 Brownii, I.xiolaena supina (both confined to sea cliffs), Frankenia paucifJora, 

 Threlkeldia diffusa, Enchylaena toinentosa, Tetragona implexicoma, Scleranthus 

 pungens, and, where less exposed to spray influence, Mesembryanthemum 

 aequilaterale, Olearia ramulosa, and Rhagodia baccata. All these must receive 

 some direct spray in stormy weather, though, owing to the open soil and good 

 run off, the local accumulation of salt will be slight. 



On top of the sheer cliffs 200 feet high, near to the source of Main Creek, 

 are a number of shallow depressions in the granite filled with rubble and clay 

 (soil Sample 6). The soil analysis shows that sodium chloride is present, also 

 a certain amount of clay, otherwise conspicuously absent in the soils. These 

 rock basins supported little vegetation (pi. iv., fig. 2). Stunted bushes of 

 Arthrocncmum halocnemoides, var. pergranulatum, occur, together with Salicornia 

 australis, Frankenia paiiciflora, and Mesembryanthemum aequilaterale. Around 

 some of the basins are the prostrate trees of Melaleuca halmaturorum referred to 

 earlier. 



True lithophytes are certain Myxophyceae that occur by the runnels made 

 by fresh water drainage over the bare rock slopes. These were quite dry in 

 January, but are most noticeable as dark olive-green to black bands across the 



