Banksia subg. Isostylis
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Banksia subg. Isostylis is a subgenus of Banksia. It contains three closely related species, all of which occur only in Southwest Western Australia. Members of subgenus Isostylis are unusual in not having Banksia's characteristic large flower spike and fruiting "cone". Flowers are instead arranged in a dome-shaped head, similar to the inflorescences of Dryandra species.
The superficial resemblance of Isostylis inflorescences to those of Dryandra has prompted the suggestion that the subgenus should be transferred to Dryandra. Other than superficial appearance, however, Isostylis has much more in common with Banksia than Dryandra. If any change is made in future, it would most likely be to promote Isostylis to genus rank.
It is generally accepted that the Isostylis subgenus provides an evolutionary link between Banksia and Dryandra, but the details remain contentious. The most recent taxonomic arrangement of Banksia is based on the view that Banksia are the most primitive group; that the Isostylis are the most advanced of the Banksia; and that Dryandra are more advanced still. There are two alternatives to this view. One alternative is that Dryanda are the most primitive group, followed by Isostylis and then the other Banksias. The other is that Isostylis are the most primitive group, and that Dryandra and Banksia co-evolved from an Isostylis-like ancestor.
There are three species of Banksia subg. Isostylis. The Holly-leaved Banksia, B. ilicifolia, is widely distributed and relatively common. The other two species, B. cuneata and B. oligantha, are rare and threatened, and are protected under the Environment Protection and Biodiversity Conservation Act 1999.
[edit] References
- George, A. S. (1981). "The Genus Banksia". Nuytsia 3 (3): 239–473.
- George, A. S. (1999). “Banksia”, Wilson, Annette (ed.) Flora of Australia: Volume 17B: Proteaceae 3: Hakea to Dryandra. CSIRO Publishing / Australian Biological Resources Study, 175–251. ISBN 0-643-06454-0.
- Taylor, Anne and Hopper, Stephen D. (1988). The Banksia Atlas (Australian Flora and Fauna Series Number 8). Canberra: Australian Government Publishing Service. ISBN 0-644-07124-9.
- Powell, Robert (1990). Leaf and Branch: Trees and Tall Shrubs of Perth. Department of Conservation and Land Management, Perth, Western Australia. ISBN 0-7309-3916-2.
[edit] External links
- Banksia subg. Isostylis at Flora of Australia Online, Department of the Environment and Heritage, Australia.
