Forest Vines to Snow Tussocks: The Story of New Zealand Plants
New Zealand Umbelliferae
New Zealand Umbelliferae
In an earlier review150 I proposed two evolutionary lines within the more notable New Zealand genera of the main subfamily of the Umbelliferae (carrot family). One included Aciphylla (spaniards) and Anisotome and is distinguished by the inflorescences arising at the centre of leaf rosettes and terminating their growth and by their dioecism (separate male and female plants). The other group, comprising Scandia, page 200Gingidia and Lignocarpa, has mostly lateral inflorescences and is mostly gynodioecious (separate female and hermaphrodite plants). In the latter group I considered Scandia to be the most primitive genus as it is semi-woody with extended stems. Scandia rosaefolia is the more shrubby of the two species of the genus and it is restricted to the northern half of the North Island and there often to mild coastal habitats. It is not difficult to imagine this species, and perhaps even woodier, now extinct, relatives, existing in New Zealand in warm pre-Ice Age times. From Scandia the completely herbaceous montane to alpine Gingidia could have evolved and also the specialised Lignocarpa of shingle slips. Since this idea was proposed a probable hybrid between Aciphylla squarrosa and Gingidia montana has been discovered in Marlborough151 which suggests that the two lines are more closely related than I thought and that all the genera concerned may have been derived from woody ancestors with a long history in New Zealand. In eastern Australia there are two species assignable to Aciphylla, one to Anisotome and three to Gingidia, including a localised occurrence of G. montana. In view of the foregoing discussion it seems more likely to me that the Australian species have a New Zealand ancestry than vice versa.
In a recent review Webb152 gives a largely opposite interpretation. He considers the few Australian species of these genera to be primitive, while New Zealand has a range from primitive to specialised forms. In contrast to my view, he regards the woodiness of Scandia as a recent specialisation. With one exception, he suggests that primitive species of these genera migrated from Australia to New Zealand with consequent diversification and specialisation here. The exception is Gingidia montana, where the localised occurrence in northern New South Wales he considers to be a case of recent migration from New Zealand to Australia.
Of course, at an earlier time before high mountains existed in New Zealand, there could have been only primitive species of these genera in both Australia and New Zealand and migration could have been in either direction. With the formation of the high mountains in New Zealand more specialised forms would then have evolved here.
According to yet another view some would argue that long distance migrations have not been involved at all. The occurrence of the same or related alpine plants in both Australia and New Zealand would derive from the time when they shared the same region before it was sundered page 201by the drifting away of the New Zealand crustal complex from Australia.
With little direct evidence from the past we can only speculate.