General Discussion

As a result of the present study it is concluded that the production of F₁ hybrids by the three local species of Acaena is quite frequent in the Wellington area. These hybrids are considered to be of two types: (1) Crosses between Acaena novaezelandiae var. pallida and A. anserinifolia (Lyall Bay-Seatoun); (2) Crosses between Acaena novae-zelandiae and A. anserinifolia (Prince of Wales Park, South Karon Stream, Wainui Valley and possibly in the Tauwharenikau Valley).

With the second type of cross a few plants of Acaena novae-zelandiae were generally found in association with the suspected hybrids. This suggests that Acaena anserinifolia normally acts as the male parent and this is probably explained by the following facts. The generally early flowering habit of Acaena anserinifolia combined with the pronounced proterogyny of all species means that when the first stigmas are appearing on the flower heads of the later flowering species only Acaena anserinifolia pollen is available. In all probability the majority of hybrids are produced in this way, and it follows that Acaena anserinifolia is most frequently the male parent.

The question aries whether the incidence of natural hybridism has always been so high or whether it is largely a recent phenomenon coinciding with the period of Europeans settlement in New Zealand. The latter view is favoured by the author, for, since European settlement, the distribution pattern of the lowland Acaenas must have been greatly altered, and as a result opportunities for hybridism must have increased immeasurably.

A comparison of pre- and post-European times with respect to conditions of dispersal and the extent of available habitats should make this clear.

In pre-Europeans times the only agents for achene dispersal were the Maori and his dog and possibly some of the flightless birds. There are no antive land mammals in New Zealand and the Maori had no form of animal husbandry. In these times, too, the country was largely covered with forest, so open habitats suitable for Acaena were much less common than now. With white settlement came the introduction of domesticated animals, notably sheep, and other animals which became established in the wild—deer, pigs and rabbits. In time the lowland areas were cleared of forest and brought into cultivation, and since that time the creation of disturbed habitats by roading and other construction works has been a recurring phenomenon. Thus, settlement has caused a marked increase in the number of dispersal agents and a parallel increase in the total area of habitats suitable for Acaena.^*. The result has been an overlapping of the three species throughout their ranges, and a consequent increase in the opportunities for hybridism.