| Juvenile and adult forms |
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Juvenile and adult forms
One of the intriguing features of the New Zealand flora is the high % of plants which have a distinctly different leaf shape or growth habit as a juvenile compared to that of the adult.
The theories put forward to account for this centre on the different environmental factors, both living and non living, present close to the ground, in the case of the juvenile, and higher in the canopy or under story for the adult. A coarse or unpalatable leaf may hinder browsers close to the ground, while as a tree with a trunk over the height that a browser may reach may mean the juvenile leaf is inefficient and unnecessary in a highlight environment of the canopy. The NZ browser may have been Moa.
Pseudopanax crassifolium lancewood is the most well known NZ native plant that adopts this habit. The juvenile may have an unbranched habit with a coarsely serrated leaf of dimensions 4cm wide and 35cm long, while the adult forms a branched canopy tree with a smooth edged leaf of dimensions 6cm wide and 25 cm long. In comparing the 2 leaf types one could be forgiven in thinking they were 2 distinct species. In fact, colonial botanists did classify them as distinct species.
The adult form
The juvenile form
A juvenile leaf with its toothed margin
Dacrydium kirkii monoao is a conifer which also has strikingly different leaf shapes as the picture shows.
The adult form is on the left, the juvenile on the right
These branches are on the same tree
Many plants adopt a divaricating or twisted form while juvenile, then adopt a more conventional shrub or tree form when they mature. Kowhai, Totara, and Matai all do this.
Whatever the reasons or advantages to the plant for this feature, it reiterates the fact that the New Zealand flora is one of the most interesting in the world.
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