Friday, June 21, 2013

Our local Banksias

Tree Banksia  Banksia integrifolia
Banksias come into their own in winter, with their nectar-rich flowers feeding birds and insects at a time when other food sources might be hard to find.
Banksia integrifolia is the only banksia species native to our local basalt soils. It is also Australia’s only tree-sized banksia. Despite the often-used common name, "coast banksia", its natural range extends almost as far west as Goondiwindi. It needs very well-drained soil, so is more usually found on sandy than basalt soils, but it grows well in the light red basalt soil at the crest of the Range.

The one native to red soil at Highfields (and shown in the photos in this post) was identified for me at the Qld herbarium as the northern subspecies Banksia integrifolia subsp. compar. However, on another occasion, another herbarium botanist identified trees over the road as Banksia integrifolia subsp. integrifolia, a plant whose range extends as far south as Victoria. I can only think that the truth of the matter is that we live in an area where the two subspecies overlap, and that our locals are intergrades, but I am happy to be corrected!
Our local subspecies, whatever it is, rarely reaches more than 5 metres tall, so is a good choice for garden use. Plants grown from local seed are worth procuring (or grown from seed collected in spring) as they are likely to be hardier to frost and drought than plants sourced from more coastal areas.
Young flowers are green,

maturing to yellow with a slight hint of pink.

Leaves on young plants are quite toothy, but as the plants mature, they become smooth-edged. They grow in whorls of about 3-5, which gives the trees a distinctive look. Even from a distance, it can’t be mistaken for any other tree.

I don’t know the age of this specimen, but doubt if it would be more than ten years old. Older plants get broader, rather than taller.

Like most Banksias, this tree has a lignotuber  - a woody, swollen trunk base, just below ground level. Lignotubers are an adaptation to fire, which may – with some difficulty in the case of this hardy plant - kill off the whole plant above-ground. Below, though, it remains alive and well, and will re-sprout with vigorous multiple stems in the next rain. Trees which don’t suffer this misfortune develop lovely twisted and gnarled old branches. 
The advantage of lignotubers in the garden is that the plants which have them can be pruned hard, to keep them shrub-sized.

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