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Species at their Southernmost Limit.
The following eighteen species probably here reach their southernmost limit on the eastern coast. Some are to be found farther south on the west coast. I give, where possible, some notes on their northward distribution.
Alectryon excelsum.—Abundant to the north of the Hurunui, and probably to be found in coastal valleys as far south as the mouth of the Waipara (Double Corner).
Angelica rosaefolia.—If correctly reported by Kaoul from Akaroa this shows a remarkably discontinuous distribution, as it is not otherwise known outside the North Island.
Clematis Colensoi.—Found also on the foothills to the west; ocal on the peninsula.
Cordyline indivisa.—Does not occur on the coastal hills of North Canterbury, and I have seen no record of it from the Kaikouras, where, however, it may be expected to occur.
Corynocarpus laevigata.—Common on the Kaikoura coast and as far south as Gore Bay; a single tree at Manuka Bay, north of the Hurunui; but does not, I think, occur between the mouth of the Hurunui and Banks Peninsula.
Cyathea Cunninghamii. — If the determination be correct this is a remarkable southern extension of its range on the east of the South Island, but in Westland it extends beyond the Big Wanganui River.
Dodonaea viscosa.—Common along the coast to the north of Pegasus Bay.
Griselinia lucida.—I have not seen this south of Banks Peninsula, and doubt its occurrence, though reported in the Manual as not uncommon as far south as the Bluff. To the north of Banks Peninsula I have noted its occurrence at Manuka Bay, where typical specimens are to be seen on rocks, just to the north of the mouth of the Hurunui. It is not reported in the Dunedin Field Club's Catalogue (1916).
Hedycarya arborea.—On the Kaikoura coast, but I have not seen it between the Amuri Bluff and Banks Peninsula. It is curious that on the west coast it should occur as far south as Preservation Inlet, but it does not pass beyond Banks Peninsula here. Possibly the arid Canterbury Plains have proved a barrier to its southward progress.
Leucopogon fasciculatum.—Occurs inland on Mount Grey downs and in the Lee Valley.
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Mariscus ustulatus.—Occurs at Gore Bay. It is reported from North Otago by Buchanan, but this requires confirmation.
Macropiper excelsum.—Common on the coastal hills to the north, but not on the plains.
Pittosporum obcordatum.—If Raoul's Akaroa record is correct this disappearing species shows remarkable discontinuity of distribution. Only known elsewhere from near Kaitaia.
Rhopalostylis sapida.—Does not occur on the coastal hills of North Canterbury, but is found on the Kaikoura coast as far south at least as Hundalee.
Rhagodia nutans.—Not uncommon near the coast at least as far south as Banks Peninsula.
Spiranthes australis.—Not known elsewhere on the east coast of this Island.
Tetrapathaea australis.—I do not know the nearest point where this plant is to be found north of Banks Peninsula, but it does not occur in northern Canterbury, nor, I think, at Kaikoura.
Zoysia pungens is found on the beaches immediately to the north, and shows no discontinuity of distribution.
It thus appears that Banks Peninsula is the southern terminus of a large number of northern species. On the other hand, few if any southern species find here their northern limit; Olearia fiagrantissima is perhaps one. This suggests a southern drift of species; for, of course, most of the northern species could live as well on the Otago coast as in Banks Peninsula. On the west coast, where there has been no such barrier as the long treeless stretch between Banks Peninsula and Timaru, some of these species have drifted much farther south—e.g., Cordyline indivisa, Hedycarya arborea, and Rhopalostylis sapida. Obviously the frosts of the plains tend to inhibit the occurrence of the more tender species.