Banksia - Background
Introduction
Banksia is a genus of about 78 species in the Protea family (Proteaceae). All species occur in Australia with one (B.dentata) extending to islands to Australia's north. Banksias can be found in most environments; the tropics, sub-alpine areas, the coast and desert areas. The most diversity in the genus occurs in the south of Western Australia where over 80% of the species occur. Banksia is very closely related to Dryandra - so much so that many authorities have subsumed Dryandra into a greatly expanded Banksia genus (see 'Expanding the Genus Banksia? below).
Discovery
Archaeological evidence suggests that banksias or Banksia-like plants have existed for over 40 million years. The first humans to discover and make use of Banksia plants were the Australian aborigines who used the nectar from the flowers as part of their diet.
The first Europeans to observe banksias were probably Dutch explorers who made several landfalls along the West Australian coast during the 17th and early 18th centuries. No botanical collections were made, however, until the discovery of the east coast of Australia by Captain James Cook in the Endeavour in April 1770. Accompanying Cook were botanists Joseph Banks and Daniel Solander who collected many new species at Botany Bay including four which would later be included in a new genus, Banksia, named in honour of Joseph Banks' contribution to botany. The four species collected were B.serrata, B.ericifolia, B.integrifolia and B.robur. Later, on the same voyage, Banks and Solander collected a fifth species (B.dentata) on the north Queensland coast.
New banksias are still being discovered from time to time. Recent discoveries include:
- Banksia rosserae - Near Mt Magnet, Western Australia (2002)
- Banksia croajingolensis - East Gippsland, Victoria (2007)
Expanding the Genus Banksia?
A paper published in February 2007 (see below) proposed that the genus Dryandra be subsumed into Banksia. The paper published new names in Banksia for all (then) currently recognised Dryandra species. This revised classification has been accepted by the Council of Heads of Australasian Herbaria and the new names now appear on Florabase (the website for the Western Australian Herbarium) and in the Australian Plant Census, which is the main online reference for names of Australian native plants.
Mast A R and Thiele K; The transfer of Dryandra R.Br. to Banksia L.f. (Proteaceae); Australian Systematic Botany, 26 February 2007
In effect, this reclassification increases the number of Banksia species to over 200 but the revised classification has not met with universal approval. For example, Alex George, a highly respected authority on both Banksia and Dryandra, strongly opposes the change on scientific grounds. The two opposing views are set out in the following articles:
- You don't have to call Dryandra Banksia" by Alex George.
- Why dryandras have changed their name by Kevin Thiele.
The differing views on the classification of Dryandra present a problem for ANPSA. Usually we follow the lead of the various Australian herbaria but, in this case, the opposing view cannot be overlooked. At this stage ANPSA is retaining Dryandra as a separate genus but the situation will be kept under review. On the ANPSA website, the revised names in the genus Banksia will also be mentioned alongside the Dryandra names, where appropriate, to minimize confusion.
However, a complicating factor is that there are a number of dryandras that have not yet been formally classified. These will undoubtedly be published, eventually, as Banksia species (i.e. there will probably be no alternative Dryandra names available). In fact, this has already occurred with the recent (2009) publishing of Banksia recurvistylis, a plant closely allied to Dryandra (Banksia) meganotia and which has no name in Dryandra (other than the non-specific Dryandra sp. aff. meganotia).
Characteristics of Banksia
Leaving aside the issue of including Dryandra within Banksia, banksias can be classified into two broad groups; sub-genus Isostylis and sub-genus Banksia. The former consists of only three species, all native to Western Australia, and is recognised by having flowers in cone-shaped clusters. This group is similar in many ways to Dryandra. The sub-genus Banksia has its flowers arranged in the more or less cylindrical spike familiar to most Australians.
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| Family Relationships: Left: Banksia menziesii, a 'typical' Banksia with vertical flower spike (subgenus Banksia). Centre: Banksia cuneata (subgenus Isostylis). Right: Dryandra quercifolia Photos: Jim Barrow, Brian Walters |
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Banksia flowers are quite small but they occur in dense clusters which, in some species, can number several thousand individuals. The sequence of opening of each flower goes through several stages:
- In bud, each flower appears as an elongated narrow tube (the perianth) comprising four segments each having an anther containing pollen at its tip.
- As the flower opens, the perianth segments separate to reveal a narrow style. Just before the flower fully opens the anthers transfer their pollen to the tip of the style (the stigma)
- Finally, the style separates from the perianth. At this stage the style and stigma, with attached pollen, is called a 'pollen presenter' (i.e. it is 'presenting' the pollen to a pollinator, usually a bird or small marsupial, which acts as the agent to transfer pollen from one flower to another for fertilisation.
This sequence is shown in the diagram below and is fairly typical of most members of the Protaceae.
Banksia flowers are followed by large, woody seed "cones" in which the seeds are contained within closed follicles, two seeds per follicle. In the majority of species these follicles remain tightly closed unless stimulated to open by heat, such as following a bushfire but, with a few species, the seed is released annually. The seeds themselves have a papery wing which allows them to be distributed by wind.
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| Left: Stages of opening of a Banksia flower. Right: Opened seed follicles after a fire Photos: Brian Walters |
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Most banksias are medium shrubs but some are prostrate and a few can become large trees. Those species native to areas where fires occur at regular intervals often have a "lignotuber", a woody swelling at or below ground level from which regeneration of the plant can occur if the above ground stems are destroyed. Other species are killed in fire, with seedlings sprouting in their place.