Banksia prionotes
Banksia prionotes | |
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Scientific classification | |
Kingdom: | Plantae |
Clade: | Tracheophytes |
Clade: | Angiosperms |
Clade: | Eudicots |
Order: | Proteales |
Family: | Proteaceae |
Genus: | Banksia |
Species: | B. prionotes
|
Binomial name | |
Banksia prionotes | |
Synonyms[1] | |
Sirmuellera prionotes (Lindl.) Kuntze |
Banksia prionotes, commonly known as acorn banksia or orange banksia, is a species of
Banksia prionotes was first described in 1840 by English botanist
Description
Banksia prionotes grows as a tree up to 10 m (30 ft) high in southern parts of its distribution, but in northern parts it is usually a shorter tree or spreading shrub, reaching about 4 m (13 ft) in height; it diminishes in size as the climate becomes warmer and drier further north.
Flowers occur in a typical Banksia flower spike, an inflorescence made up of hundreds of small individual flowers, or florets, densely packed around a cylindrical axis. B. prionotes has cream-coloured flowers with a bright orange limb that is not revealed until the flower fully opens. Known as anthesis, this process sweeps through the inflorescence from bottom to top over a period of days, creating the effect of a cream inflorescence that progressively turns bright orange. The old flower parts fall away after flowering finishes, revealing the axis, which may bear up to 60 embedded follicles. Oval or oblong in shape and initially covered in fine hairs, these follicles are from 14 to 20 mm (1⁄2 to 3⁄4 in) long and 6–11 mm (1⁄4–3⁄8 in) wide, and protrude 3–6 mm (1⁄8–1⁄4 in) from the cone. Inside, they bear two seeds separated by a brownish woody seed separator. The matte blackish seeds are wedge-shaped (cuneate) and measure 8–10 mm (3⁄8–3⁄8 in) long by 5–6 mm (1⁄4–1⁄4 in) wide with a membranous 'wing'.[3][4]
The root system consists of a main
Taxonomy
Banksia prionotes was first published by English botanist
The most commonly reported common names of B. prionotes are acorn banksia, derived from the resemblance of partly opened inflorescences to acorns;[10] and orange banksia.[11][12] Other reported common names include saw-toothed banksia[13] and golden banksia[14] Bwongka is a generic Noongar name for Banksia in the Avon River catchment, where B. prionotes is one of several species occurring.[15]
No further subspecies or varieties of B. prionotes have been described, and it has no
George's arrangement remained current until 1996, when Kevin Thiele and Pauline Ladiges published an arrangement informed by a cladistic analysis of morphological characteristics. Their arrangement maintained B. prionotes in B. subg. Banksia, but discarded George's sections and his series Crocinae. Instead, B. prionotes was placed at the end of series Banksia, in subseries Cratistylis.[19] Questioning the emphasis on cladistics in Thiele and Ladiges' arrangement, George published a slightly modified version of his 1981 arrangement in his 1999 treatment of Banksia for the Flora of Australia series of monographs. To date, this remains the most recent comprehensive arrangement. The placement of B. prionotes in George's 1999 arrangement may be summarised as follows:[4]
- Banksia
- B. subg. Banksia
- B. sect. Banksia
- B. ser. Salicinae (11 species, 7 subspecies)
- B. ser. Grandes (2 species)
- B. ser. Banksia (8 species)
- B. ser. Crocinae
- B. prionotes
- B. burdettii
- B. hookeriana
- B. victoriae
- B. ser. Prostratae (6 species, 3 varieties)
- B. ser. Cyrtostylis (13 species)
- B. ser. Tetragonae (3 species)
- B. ser. Bauerinae(1 species)
- B. ser. Quercinae (2 species)
- B. sect. Coccinea(1 species)
- B. sect. Oncostylis (4 series, 22 species, 4 subspecies, 11 varieties)
- B. sect. Banksia
- B. subg. Isostylis (3 species)
- B. subg. Banksia
Since 1998, American botanist
Hybrids
With Banksia hookeriana
Banksia prionotes readily hybridises with Banksia hookeriana (Hooker's banksia) under experimental conditions, indicating that these species have highly compatible pollen.[24] The cultivar B. 'Waite Orange' is believed to be such a hybrid, having arisen by open pollination during a breeding experiment conducted at the Waite Agricultural Research Institute of the University of Adelaide in 1988.[25]
Banksia prionotes × hookeriana has also been verified as occurring in the wild, but only in disturbed locations. The two parent species have overlapping ranges and are pollinated by the same honeyeater species; and though preferring different soils, they often occur near enough to each other for pollinators to move between them. It therefore appears that the only barrier to hybridisation in undisturbed areas is the different flowering seasons: B. prionotes has usually finished flowering by the end of May, whereas flowering of B. hookeriana usually does not begin until June. In disturbed areas, however, the increased runoff and reduced competition mean extra nutrients are available, and this results in larger plants with more flowers and a longer flowering season. Thus the flowering seasons overlap, and the sole barrier to interbreeding is removed. The resultant F1 hybrids are fully fertile, with seed production rates similar to that of the parent species. There is no barrier to backcrossing of hybrids with parent species, and in some populations this has resulted in hybrid swarms. This raises the possibility of the parent species gradually losing their genetic integrity, especially if the intermediate characteristics of the hybrid offer it a competitive advantage over the parent species, such as a wider habitat tolerance. Moreover, speciation might occur if the hybrid's intermediate characteristics allow it to occupy a habitat unsuited to both parents, such as an intermediate soil type.[26]
Banksia prionotes × hookeriana hybrids have characteristics intermediate between the two parents. For example, the first putative hybrids studied had a habit "like that of gigantic B. hookerana [sic]", having inherited the size of B. prionotes, together with B. hookeriana's tendency to branch from near the base of the trunk. Similarly, the infructescences were like B. prionotes in size, but had persistent flowers like B. hookeriana. Inflorescences and leaves were intermediate in size and shape, and bark was like that of B. prionotes.[27]
Other putative hybrids
During data collection for The Banksia Atlas project, a single presumed natural hybrid between B. prionotes and B. lindleyana (porcupine banksia), with fruit like B. lindleyana but leaves intermediate between the two parents, was found north of Kalbarri National Park. At the time this was considered an important discovery, as the parent species were thought not to be closely related.[28] Mast's analyses, however, place them both in a clade of eight species, though B. lindleyana remains less closely related to B. prionotes than B. hookeriana.[21] Hybrids of B. prionotes with B. menziesii (firewood banksia) have also been produced by artificial means,[29] and presumed natural hybrids have been recorded.[28]
Distribution and habitat
Banksia prionotes occurs throughout much of the
It is most common amongst the
The soils east of the
The species is almost totally restricted to the
Ecology and physiology
Growth
The structure of the root system, comprising a vertical tap root and multiple horizontal laterals, develops in the seedling's first year. Thereafter, the sinker and laterals continue to lengthen, and new laterals appear. There are only three to five laterals at first, but this number typically increases to eight to ten within ten years. During the first winter, there is a great deal of root system development, especially elongation of the sinker root, but almost no shoot growth. By summer, the sinker root has generally almost reached the water table, and shoot growth increases substantially. Around February, the shoot forms a resting bud, and growth then ceases until October. On resumption of shoot growth, the shoots grow rapidly for a short time, while the plant is under little water stress; then, with the onset of water stress, the plants settles into a long period of slower shoot growth. This pattern of summer-only shoot growth is maintained throughout the life of the plant, except that in mature plants, seasonal shoot growth may cease with the formation of a terminal inflorescence rather than a resting bud.[7][39] Inflorescence development continues after shoot growth ceases, and flowering commences in February or March. March and April are the peak months for flowering, which ends in July or August.[28]
Annual growth increases exponentially for the first eight years or so, but then slows down as resources are diverted into reproduction and the greater density of foliage results in reduced photosynthetic efficiency.[39]
Nutrition and metabolism
The root structure of B. prionotes exhibits two common environmental adaptations. Firstly, this species is phreatophytic, that is, its long taproot extends down to the water table, securing it a continuous water supply through the dry summer months, when surface water is generally unavailable. This not only helps ensure survival over summer, but allows plants to grow then. Though the supply of water is the taproot's primary function, the ground water obtained typically contains ionic concentrations of chloride, sodium, magnesium, calcium and potassium that are adequate for the plant's nutritional needs.[5][40]
The other common adaptation is the possession of
The uptake of nutrient and water by the cluster roots peaks through winter and spring, but ceases when the upper layer of soil dries out in summer. The cluster roots are then allowed to die, but the laterals are protected from desiccation by a continuous supply of water from the sinker root.[5][40][41] The water supplied to the laterals by the sinker root is continually lost to the soil; thus this plant facilitates the movement of ground water from the water table into surface soil, a process known as hydraulic redistribution.[42] Cluster roots have been estimated as comprising about 30% of total root biomass in this species; the seasonal production of so much biomass, only for it to be lost at the end of the growing season, represents a substantial investment by the plant, but one that is critical in the competition for nutrients.[39]
During winter, asparagine is
Breeding system
Flowering begins in February and is usually finished by the end of June. The species has an unusually low rate of flowering: even at the peak of its flowering season, it averages less than seven inflorescences per plant flowering at any one time. Individual flowers open sequentially from bottom to top within each inflorescence, the rate varying with the time of day: more flowers open during the day than at night, with a peak rate of around two to three florets per hour during the first few hours of daylight, when honeyeater foraging is also at its peak.[43]
The flowers are fed at by a range of
Honeyeaters prefer to forage at individual flowers which have only just opened, as these offer the most nectar. As they probe for nectar, honeyeaters end up with large quantities of pollen on their beaks, foreheads and throats, some of which they subsequently transfer to other flowers. This transfer is quite efficient: flowers typically lose nearly all their pollen within four hours of opening, and pollen is deposited on the majority of stigmata. Around 15% of these stigmata end up with pollen lodged in the stigmatic groove, a prerequisite to fertilisation.[43]
The structure of the Banksia flower, with the style end functioning as a
If it does occur, protandry does nothing to prevent
Cone production varies a great deal from year to year, but, as a result of its low flowering rate, is generally very low. However, there are typically a very high number of follicles per cone, leading to relatively high seed counts.[45] There is some seed predation, primarily from the curculionid weevil Cechides amoenus.[46]
Response to fire
Like many plants in
The actual degree of serotiny and fire mortality in B. prionotes varies with latitude, or, more likely, climate. Observations suggest that it is always killed by fire in the north of its range, which is relatively hot and dry, and where individual plants are usually smaller, but may survive fire in the cooler, moister, south. Moreover, it is essentially non-serotinous in the south, since all seed is released by the end of the second year, but seed retention increases steadily to the north, and at the northern end of its range, it typically takes around four years for a plant to release half of its seed in the absence of bushfire, with some seed retained for up to 12 years.[48]
A number of other characteristics of B. prionotes can be understood as secondary responses to weak serotiny. For example, winter flowering ensures that seed is ripe by the beginning of the bushfire season; this is very important for weakly serotinous species, which rely heavily upon the current year's seed crop.[45] Another example is the deciduous florets of B. prionotes. In strongly serotinous species, the old florets are retained on the cones, where they function as fire fuel, helping to ensure that follicles reach temperatures sufficient to trigger seed release. In B. prionotes, however, seed release is triggered at relatively low temperatures: in one study, 50% of follicles opened at 265 °C (509 °F), and 90% opened at 330 °C (626 °F); in contrast, the closely related but strongly serotinous B. hookeriana required 340 and 500 °C (644 and 932 °F) respectively. Floret retention would therefore be to no advantage, and might even prevent seed from escaping spontaneously opened follicles.[49]
Seed release in B. prionotes is promoted by repeated wetting of the cones. The
Because of its higher susceptibility and lower reliance on fire for reproduction, the optimal fire interval for B. prionotes is higher than for other Banksia species with which it occurs. One simulation suggested an interval of 18 years was optimal for B. prionotes, compared to 15 years for B. hookeriana and 11 years for B. attenuata. The same model suggested that B. prionotes is quite susceptible to reductions in fire intervals. On the other hand, it shows little susceptibility to increases in fire interval: although senescence and death are often observed in plants older than about 30 years, healthy stands have been observed that have escaped fire for 50 years. These stands have a multi-aged structure, demonstrating the occurrence of successful inter-fire recruitment.[36][51]
Fire response may also furnish an explanation for the
Conservation
Banksia prionotes is susceptible to a number of threatening processes. It is highly susceptible to Phytophthora cinnamomi dieback;[53][54] wild populations are harvested commercially by the cut flower industry;[9] and some of its range is subject to land clearing for urban or agricultural purposes. An assessment of the potential impact of climate change on this species found that severe change is likely to lead to a reduction in its range of around 50% by 2080; and even mild change is projected to cause a reduction of 30%; but under mid-severity scenarios the distribution may actually grow, depending on how effectively it can migrate into newly habitable areas.[55] However, this study does not address the potential of climate change to alter fire regimes; these have already been impacted by the arrival of humans, and this change is thought to have led to a decline in the abundance and range of B. prionotes.[35]
The species as a whole is not considered particularly
Cultivation
Described as "an outstanding ornamental species" by
It is fairly easy to grow in areas with a
The species is also considered ideal for cut flower production, as its flowers fulfill the commercial criteria of terminal blooms and a long stem length.
References
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- ^ ASGAP. Archived from the originalon 12 May 2008. Retrieved 22 August 2009.
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- ^ "Australian Plant Common Names Database". Australian National Botanic Gardens website. Canberra: Department of the Environment and Heritage. Archived from the original on 11 July 2009. Retrieved 22 August 2009.
- ^ Perth Zoo (2006). "Acorn Banksia". Perth Zoo website. Government of Western Australia. Archived from the original on 3 July 2009. Retrieved 8 July 2009.
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- ^ Aboriginal NRM (2009). "Nyungar NRM Wordlist & Language Collection Booklet of the Avon Catchment Region" (PDF). Avon Catchment Council website. Avon Catchment Council. Archived from the original (PDF) on 19 February 2011. Retrieved 8 July 2009.
- ^ "Sirmuellera prionotes (Lindl.) Kuntze". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.
- Prodromus systematis naturalis regni vegetabilis. Vol. 14. Paris: Sumptibus Sociorum Treuttel et Wurtz.
- ^ Bentham, George (1870). "Banksia". Flora Australiensis. Vol. 5. London: L. Reeve & Co. pp. 541–62.
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- ^ Groom, P. K. (2004). "Seedling growth and physiological responses of two sandplain Banksia species differing in flood tolerance" (PDF). Journal of the Royal Society of Western Australia. 87 (3): 115–21. Archived from the original (PDF) on 21 February 2011. Retrieved 9 July 2009.
- ^ Groom, P. K.; Froend, R. H.; Mattiske, E. M.; Gurner, R. P. (2001). "Long-term changes in vigour and distribution of Banksia and Melaleuca overstorey species on the Swan Coastal Plain". Journal of the Royal Society of Western Australia. 84: 63–69.
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- ^ Cowling, Richard M.; Lamont, Byron B.; Enright, Neal J. (1990). "Fire and management of south-western Australian banksias". Proceedings of the Ecological Society of Australia. 16: 177–83.
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- ^ "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. Archived from the original (PDF) on 5 March 2011. Retrieved 22 August 2009.
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- ^ Chow, Wendy; Creese, Sonja (June 2008). "A hydrological investigation of a Banksia prionotes community on transported yellow sands". Watsnu: Species and Communities Branch Newsletter for Threatened Species and Ecological Communities Conservation. 14 (1): 5. Archived from the original on 20 July 2011. Retrieved 6 August 2009.
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External links
- "Banksia prionotes Lindl". Flora of Australia Online. Department of the Environment and Heritage, Australian Government.
- "Banksia prionotes Lindl". Department of Biodiversity, Conservation and Attractions.
- "Banksia prionotes Lindl". Australian Plant Name Index (APNI), IBIS database. Centre for Plant Biodiversity Research, Australian Government.