Banksia violacea
| Violet Banksia | |
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| Inflorescence of Banksia violacea | |
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| Species: | B. violacea
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| Binomial name | |
| Banksia violacea | |
Banksia violacea, commonly known as Violet Banksia, is a species of shrub or tree in the plant genus Banksia (family Proteaceae). It is generally encountered as a small shrub to 1.5 m (5 ft) high with fine narrow leaves, and is best known for its unusually coloured dark purple-violet inflorescences. It is found in low shrubland in southern regions of Western Australia from Esperance in the east to Narrogin in the west, growing exclusively in sandy soils. It is pollinated by, and is a food source for, birds and insects.
First described in 1927 by Western Australian botanist Charles Gardner, the species was at one stage considered a variety of B. sphaerocarpa. There are no subspecies or varieties recognised. Banksia violacea is classified as Not Threatened under the Wildlife Conservation Act of Western Australia. Regarded of no value to floriculture, it is rarely seen in cultivation.
Description
Banksia violacea grows as a shrub up to 1.5 m (5 ft) tall, with narrow leaves which are 1–2 cm (0.4–0.8 in) long and about 1.5 millimetres wide. Flowers occur in typical Banksia "flower spikes", and the inflorescences are made up of hundreds of pairs of flowers densely packed in a spiral around a woody axis. B. violacea's flower spike is roughly spherical, with a diameter of 2–3 cm (0.8–1.2 in). Unusually for Banksia species, the inflorescences are often violet in colour, ranging anywhere from a dark violet-black through various combinations of violet and greenish-yellow in less pigmented blooms. Each flower consists of a tubular perianth made up of four fused tepals, and one long wiry style. The styles are hooked rather than straight, and are initially trapped inside the upper perianth parts, but break free at anthesis. The fruiting structure is a stout woody "cone", with a hairy appearance caused by the persistence of old withered flower parts.[1] The follicles when young are greenish in colour and covered in fine white hairs, fading to tan or grey with age.
Taxonomy
Discovery and naming
The type specimen of Banksia violacea was collected by Western Australian botanist Charles Gardner on 14 December 1926, in the vicinity of Lake Grace. The following year, he published a description of the species in Journal and Proceedings of the Royal Society of Western Australia.[2] He placed it in section Oncostylis of Bentham's taxonomic arrangement of Banksia, giving it the specific epithet "violacea" in reference to the violet flowers. Thus the full name of the species, with author citation, is Banksia violacea C.A.Gardner.[3]
Banksia violacea has been considered a variety of B. sphaerocarpa (Fox Banksia);[4] this view was published by William Blackall in his 1954 How to Know Western Australian Wildflowers. He omitted B. violacea, instead treating it under the entry for B. sphaerocarpa with the text "Fls violet = var violacea".[5] This was an invalid publication, however, and a nomen nudum. In 1981 Alex George declared Banksia sphaerocarpa var. violacea Blackall a nomenclatural synonym of B. violacea.[3][6]
Infrageneric placement
In George's 1981 arrangement, B. violacea was placed in subgenus Banksia because its inflorescence is a typical Banksia "flower spike"; section Oncostylis because of its hooked styles; and series Abietinae because its inflorescence is roughly spherical. It was placed in taxonomic sequence between B. incana (Hoary Banksia) and B. meisneri (Meissner's Banksia).[6]
In 1996, Kevin Thiele and Pauline Ladiges published the results of a cladistic analysis of morphological characters of Banksia. They retained George's subgenera and many of his series, but discarded his sections. B. ser. Abietinae was found to be very nearly monophyletic, and so retained. It further resolved into four subclades, so Thiele and Ladiges split it into four subseries. B. violacea appeared in the last of these:[7]
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B. violacea | |
This clade became the basis of B. subseries Longistyles, which Thiele defined as containing those taxa with very long and slender styles, and with smoothly convex perianth limbs without a costal ridge and with thickened margins. In accordance with their cladogram, their arrangement placed B. violacea first in phyletic order, followed by B. laricina (Rose-fruited Banksia).[7]
Thiele and Ladiges' arrangement was not accepted by George, who, questioning the emphasis on cladistics, rejected most of their changes in his 1999 arrangement. B. series Abietinae was restored to George's 1981 broader circumscription, and all of Thiele and Ladiges' subseries were abandoned. George commented that the species has no close relatives, being "loosely allied" to B. sphaerocarpa (Fox Banksia) and B. telmatiaea (Swamp Fox Banksia). Despite this, the phyletic ordering of the series was altered so that B. violacea fell between B. scabrella (Burma Road Banksia) and B. incana.[1]
B. violacea's placement in George's arrangement may be summarised as follows:[1]
- Banksia
- B. subg. Banksia
- B. sect. Banksia (9 series, 50 species, 9 subspecies, 3 varieties)
- B. sect. Coccinea (1 species)
- B. sect. Oncostylis
- B. ser. Spicigerae (7 species, 2 subspecies, 4 varieties)
- B. ser. Tricuspidae (1 species)
- B. ser. Dryandroideae (1 species)
- B. ser. Abietinae
- B. sphaerocarpa (3 varieties)
- B. micrantha
- B. grossa
- B. telmatiaea
- B. leptophylla (2 varieties)
- B. lanata
- B. scabrella
- B. violacea
- B. incana
- B. laricina
- B. pulchella
- B. meisneri (2 subspecies)
- B. nutans (2 varieties)
- B. subg. Isostylis (3 species)
- B. subg. Banksia
Since 1998, American botanist Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae. His analyses suggest an arrangement phylogeny that is very greatly different to George's, and somewhat different to Thiele and Ladiges'. With respect to B. violacea, Mast's results agree with its placement near B. laricina and B. incana, placing it in a clade with these two species and B. sphaerocarpa var. dolichostyla (treated at species rank as B. dolichostyla):
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B. dolichostyla | |
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B. violacea | |
However, Thiele's B. subseries Longistyles appears to be polyphyletic, as do both definitions of B. ser. Abietinae—that is, none form a natural grouping.[8][9][10]
Early in 2007, Mast and Thiele initiated a rearrangement of Banksia by merging Dryandra into it, and publishing B. subgenus Spathulatae for the taxa having spoon-shaped cotyledons. They foreshadowed publishing a full arrangement once DNA sampling of Dryandra was complete; in the meantime, if Mast and Thiele's nomenclatural changes are taken as an interim arrangement, then B. violacea is placed in B. subgenus Spathulatae.[11]
Distribution and habitat
B. violacea occurs in southern regions of Western Australia, from Woodanilling to Esperance and as far north as Hyden.[1][13] This distribution includes areas of the Avon Wheatbelt, Esperance Plains and Mallee biogeographic regions.[12] It favours white sandy soils, often overlying laterite, clay or quartzite. It usually grows among proteaceous-myrtaceous heath and shrublands.
Banksia violacea is classified as Not Threatened under the Wildlife Conservation Act of Western Australia.[12]
Ecology
Like most other Proteaceae, B. violaceae has proteoid roots, roots with dense clusters of short lateral rootlets that form a mat in the soil just below the leaf litter. These enhance solubilisation of nutrients, thus allowing nutrient uptake in low-nutrient soils such as the phosphorus-deficient native soils of Australia.
It is one of a small number of Banksia species that has both lignotuberous and non-lignotuberous populations. In both cases, plants are adapted to release their aerial seed bank following a bushfire, ensuring seedlings are established on clear and relatively fertile ground; however the possession of a lignotuber makes plants much less reliant on fire regime for population maintenance and regeneration, as maternal plants are not killed by bushfire, but resprout from below ground level. Lignotuberous plants generally occur among the north-eastern populations;[6][14] an investigation into the biogeography of these plants failed to find any vegetative, climatic or other environmental factors associated with the possession of a lignotuber.[15]
B. violacea is highly susceptible to Phytophthora cinnamomi dieback.[16]
Cultivation
B. violacea is rarely cultivated. It is a slow-growing plant that tends to become untidy with age, and probably does not flower until four to five years from seed. Flowers are an unusual colour, but occur within the bush where they are usually obscured by foliage. It tolerates light pruning not below the green foliage, except for the variant with a lignotuber, which may be pruned heavily. George recommends a sunny position in light, sandy soil.[14] Seeds do not require any treatment, and take 19 to 50 days to germinate.[17]
The species is of no value to floriculture, as the inflorescences are too small, and obscured by the foliage. It has been suggested, however, that the purple colour may be a worthwhile character to select for in plant breeding.[18]
References
- ^ a b c d George, A. S. (1999). "Banksia". In Wilson, Annette (ed.). Flora of Australia. Vol. 17B. CSIRO Publishing / Australian Biological Resources Study. pp. 175–251. ISBN 0-643-06454-0.
- ^ Gardner, C. A. (1927). "Contributiones florae Australiae occidentalis VI". Journal and Proceedings of the Royal Society of Western Australia. 13: 61–68.
- ^ a b "Banksia violacea C.A.Gardner". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.
- ^ Holliday, Ivan; Watton, Geoffrey (1975). A Field Guide to Banksias. Adelaide: Rigby. p. 136. ISBN 0-85179-864-0.
{{cite book}}: CS1 maint: multiple names: authors list (link) - ^ Blackall, W. E.; edited by B. J. Grieve (1954). How to Know Western Australian Wildflowers. Nedlands: University of Western Australia Press.
{{cite book}}:|author=has generic name (help)CS1 maint: multiple names: authors list (link) - ^ a b c George, Alex S. (1981). "The Genus Banksia L.f. (Proteaceae)". Nuytsia. 3 (3): 239–473.
- ^ a b Thiele, Kevin and Pauline Y. Ladiges (1996). "A cladistic analysis of Banksia (Proteaceae)". Australian Systematic Botany. 9 (5): 661–733. doi:10.1071/SB9960661.
- ^ Mast, Austin R. (1998). "Molecular systematics of subtribe Banksiinae (Banksia and Dryandra; Proteaceae) based on cpDNA and nrDNA sequence data: implications for taxonomy and biogeography". Australian Systematic Botany. 11: 321–342. doi:10.1071/SB97026.
- ^ Mast, Austin R. and Thomas J. Givnish (2002). "Historical biogeography and the origin of stomatal distributions in Banksia and Dryandra (Proteaceae) based on Their cpDNA phylogeny". American Journal of Botany. 89 (8): 1311–1323. doi:10.3732/ajb.89.8.1311. ISSN 0002-9122. Retrieved 2006-07-02.
- ^ Mast, Austin R., Eric H. Jones and Shawn P. Havery (2005). "An assessment of old and new DNA sequence evidence for the paraphyly of Banksia with respect to Dryandra (Proteaceae)". Australian Systematic Botany. 18 (1). CSIRO Publishing / Australian Systematic Botany Society: 75–88. doi:10.1071/SB04015.
{{cite journal}}: CS1 maint: multiple names: authors list (link) - ^ Mast, Austin R. and Kevin Thiele (2007). "The transfer of Dryandra R.Br. to Banksia L.f. (Proteaceae)". Australian Systematic Botany. 20: 63–71. doi:10.1071/SB06016.
- ^ a b c "Banksia violacea C.A.Gardner". FloraBase. Western Australian Government Department of Biodiversity, Conservation and Attractions.
- ^ Taylor, Anne; Hopper, Stephen (1988). The Banksia Atlas (Australian Flora and Fauna Series Number 8). Canberra: Australian Government Publishing Service. ISBN 0-644-07124-9.
- ^ a b George, Alex S. (1987). The Banksia Book (Second Edition). Kenthurst, New South Wales: Kangaroo Press (in association with the Society for Growing Australian Plants). ISBN 0-86417-006-8.
- ^ Lamont, Byron and Adrienne Markey (1995). "Biogeography of fire-killed and resprouting Banksia species in south-western Australia". Australian Journal of Botany. 43 (3): 283–303. doi:10.1071/BT9950283.
- ^ "Part 2, Appendix 4: The responses of native Australian plant species to Phytophthora cinnamomi" (PDF). Management of Phytophthora cinnamomi for Biodiversity Conservation in Australia. Department of the Environment and Heritage, Australian Government. 2006. Retrieved 2009-04-22.
{{cite web}}: External link in|work= - ^ Sweedman, Luke; et al. (2006). Australian seeds: a guide to their collection, identification and biology. CSIRO Publishing. p. 203. ISBN 0643092986.
{{cite book}}: Explicit use of et al. in:|author=(help) - ^ Sedgley, Margaret (1998). journal = Horticultural reviews "Banksia: New proteaceous cut flower crop". 22: 1–25.
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External links
- "Banksia violacea C.A.Gardner". Flora of Australia Online. Department of the Environment and Heritage, Australian Government.
- "Banksia violacea C.A.Gardner". FloraBase. Western Australian Government Department of Biodiversity, Conservation and Attractions.
- "Banksia violacea C.A.Gardner". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.