Appendix on the Plant-covering of the Spit.
The general character of the plant-covering of the Ellesmere Spit is determined by (a) the edaphic conditions, particularly the poverty and scantiness of the soil, which is either pure sand or a sandy gravel; (b) exposure to the sun, which is at a maximum; (c) exposure to wind, which is also at a maximum; and (d) proximity to the sea. These conditions have produced a vegetation which is markedly xerophytic with a halophytic element. In the immediate neighbourhood †
[Footnote] † I have recently seen pebbles on Karewa Island near Tauranga, high above the sea, whose presence at that level I could not account for.
hood of the sea we find a typical dune vegetation, while further back the plant-covering is almost identical with that of the lower parts of the great riverbeds, e.g. of the Waimakariri or the Rakaia. The area is dealt with by Cockayne, in Vegetation der Erde (1928) under the head of “Beach of loose stones.”
Though the soil is shallow and poor there is a very fair growth of grass and common pasture plants, both native and alien. Poa caespitosa is dominant over the greater part of the area, but not, of course, quite close to the sea. Associated with this are Stipa setacea, Festuca littoralis, F. novae-zealandiae, Carex lucida, C. breviculmis, and C. resectans, Dichelachne crinita (a small form), Danthonia pilosa, Scirpus nodosus, Leucopogon Fraseri, Vittadinia australis, Gnaphalium luteoalbum, Acaena microphylla, and A. novae-zelandiae, Cotula squalida, Erechtites quadridentata, Geranium sessiliflorum, Raoulia lutescens and R. Monroi, Muchlenbeckia ephedrioides, M. axillaris, and M. complexa, Triodia exigua, Carmichaelia Monroi, and C. subulata, Scleranthus biflorus, Pimelea prostrata, Hymenanthera crassifolia, Pteridium aquilinum, Cheilanthes Sieberi. Shrubs are represented by Discaria Toumatou (chiefly upon the raised bank which runs the whole length of the Spit (see Plate 29), Carmichaelia subulata, Clematis afoliata, Sophora tetraptera, Hymenanthera crassifolia, The dune area close to the sea is occupied by Scirpus frondosus, Calystegia Soldanella, Carex pumila, Phormium tenax (very scarce), a stunted form of Myoporum laetum, and a few exotics such as Hypochaeris radicata and Rumex acetosella. Immediately behind the dunes there are very dry barren patches and hollows chiefly occupied by Raoulia lutescens, and strong cushions of Pimelea laevigata. Pteridium aquilinum also grows very near the sea in some spots.
The principal exotics are Clovers, Rye-grass, Bromus sp., Thistles, Haresfoot Trefoil, Salad Burnet, Nettle, Erodium cicutarium, Verbascum thapsus, Polycarpon tetraphyllum, Avena fatua, Lepidium murale, and Marrubium vulgare.
The most remarkable single species of the locality is the prostrate form of Carmichaelia subulata, called by Cockayne an “epharmone” of that species. This really exists in three fairly well marked forms or grades. Sometimes it is perfectly prostrate, the single plant forming a circular patch about six feet in diameter, but all branches proceeding from one stem without any tendency to root in creeping. Many such plants are often grouped together, forming great patches twenty feet or more in diameter, the individual plants being closely matted together, and the whole mass rising to about two feet above the ground. Then there are intermediate forms, from two to three feet in height, not truly prostrate yet not as tall and erect as the species usually is. And there are also plenty of plants which grow to six feet or more in height and are in every way perfectly normal representatives of the species. All these forms differ from the typical plant, if at all, in the manner of growth only, and a close examination of the prostrate forms failed to detect anything, either in the soil or in the aspect or provision of shelter, which could at all suggest a reason why particular individuals should assume the one form rather than the other. The extreme prostrate form is of course due to wind-pressure.