Banksia aculeata

"Prickly banksia" redirects here; "prickly banksia" is also an antiquated common name for Banksia sessilis.
Banksia aculeata

Priority Two — Poorly Known Taxa (DEC)
Scientific classification
Kingdom: Plantae
(unranked): Angiosperms
(unranked): Eudicots
Order: Proteales
Family: Proteaceae
Genus: Banksia
Species: B. aculeata
Binomial name
Banksia aculeata
A.S.George

Banksia aculeata, commonly known as prickly banksia, is a species of shrub of the family proteaceae native to the Stirling Range in southwest Western Australia. One of three closely related species all of which have distinctive upside-down lantern-like inflorescences, it bears pinkish blooms in early summer. The leaves have very prickly serrated margins. A rare plant, it is found in gravelly soils in elevated areas. It is killed by fire and regenerates from seed afterwards.

Description

Banksia aculeata grows as a bushy shrub up to 2 m (7 ft) tall, with fissured grey bark and lacking a lignotuber. The leaves are from 4 to 9 cm long, and 0.8 to 3 cm wide, with sharply pointed rigid lobes on the margins. The inflorescences are from 6 to 9 cm long, and are pendulous rather than erect. The flowers are 3 to 4 cm long, pink at the base but grading into cream. The infructescence is a woody spike embedded with up to 20 massive follicles; the withered flower parts persist on the spike, giving it a hairy appearance.[1] Oval in shape, the follicles are wrinkled in texture and covered with fine hair, they are 3-4.5 cm (1.2-1.8 in) long, 2.5-3 cm (1-1.2 in) high, and 2-2.5 cm (0.8-1 in) wide.[2]

The obovate seed is 4–5 cm (1.6–2.0 in) long and fairly flattened, and is composed of the wedge-shaped seed body proper, measuring 1–1.2 cm (0.4–0.5 in) long and 1.5–1.8 cm (0.6–0.7 in) wide, and a papery wing. One side, termed the outer surface, is grey and wrinkled and the other is black and sparkles slightly. The seeds are separated by a sturdy dark brown seed separator that is roughly the same shape as the seeds with a depression where the seed body sits adjacent to it in the follicle. Seedlings have cuneate (wedge-shaped) cotyledons which measure 1.1–1.2 cm long and 1.9 cm wide. They are dull dark green, sometimes with a reddish tinge, and the margin of the wedge is convex. The auricle at the base of the cotyledon leaf is pointed and measures 0.3 cm long. The hypocotyl is thick. smooth and dark red. The obovate to oblong seedling leaves are 4-9 cm long by 2-2.5 cm wide with serrated margins, with v-shaped sinuses and sharp teeth.[2]

Taxonomy

Banksia aculeata was first collected by James Drummond on one of his three trips to the Stirling Ranges between 1843 and 1848, though he did not recognise it as distinct from B. caleyi—this was only discovered over a century later by Alex George. George described B. aculeata in his 1981 "The genus Banksia L.f. (Proteaceae)". He based the species on a specimen collected by him on Chester Pass Road in the Stirling Range east of Cranbrook on 20 March 1972. He give it the specific epithet aculeata (Latin for "sharp"), in reference to the sharply pointed leaf lobes.[2]

George placed B. aculeata in B. subg. Banksia because its inflorescence is a typical Banksia flower spike; in B. sect. Banksia because of its straight styles; and B. ser. Tetragonae because of its pendulous inflorescences. He considered its closest relative to be B. caleyi, from which it differs in having narrower leaves with fewer, larger lobes; longer perianths, which grade from red to cream rather than from cream to red; shorter pistils; and also differences in the follicles, seeds and flowering time.[2]

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. George's B. ser. Tetragonae was found to be monophyletic, and therefore retained; and their analysis of the relationships within the series supported the placement of B. aculeata alongside B. caleyi.[3]

B. aculeata's placement in Thiele and Ladiges' arrangement may be summarised as follows:[3]

Banksia
B. subg. Isostylis (3 species)
B. elegans (incertae sedis)
B. subg. Banksia
B. ser. Tetragonae
B. elderiana
B. lemanniana
B. caleyi
B. aculeata

The arrangement of Thiele and Ladiges was not accepted by George, and was discarded in his 1999 revision. Under George's 1999 arrangement, B. aculeata's placement was as follows:[1]

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 (4 species)
B. ser. Prostratae (6 species, 3 varieties)
B. ser. Cyrtostylis (13 species)
B. ser. Tetragonae
B. lemanniana
B. caleyi
B. aculeata

Since 1998, Austin Mast has been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae. His analyses suggest a phylogeny that is rather different from previous taxonomic arrangements, but support the placement of B. aculeata alongside B. caleyi in a clade corresponding closely with B. ser. Tetragonae.[4][5][6]

Early in 2007 Mast and Thiele initiated a rearrangement by transferring Dryandra to Banksia, and publishing B. subg. Spathulatae for the species having spoon-shaped cotyledons; in this way they also redefined the autonym B. subg. Banksia. 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. aculeata is placed in B. subg. Banksia.[7]

Distribution and habitat

Distribution within Western Australia

B. aculeata is native to the foothills of the Stirling Range, occurring at elevations between 250 and 500 m, in shrubland in gravelly, clayish soils. It is a fairly rare plant, with most populations consisting of fewer than 100 plants.[8]

Ecology

Like many plants in south-west Western Australia, Banksia aculeata is adapted to an environment in which bushfire events are relatively frequent. Most Banksia species can be placed in one of two broad groups according to their response to fire: reseeders are killed by fire, but fire also triggers the release of their canopy seed bank, thus promoting recruitment of the next generation; resprouters survive fire, resprouting from a lignotuber or, more rarely, epicormic buds protected by thick bark.[9] It is killed by fire because it possesses neither thick protective bark nor a lignotuber to reshoot from. However it is serotinous—it accumulates an aerial seed bank that is released only in response to fire—so populations typically recover rapidly after fire. This strategy makes it depend upon a suitable fire regime, however. Plants take three to four years to reach flowering after a bushfire.[8]

Banksia aculeata has previously been reported as moderately susceptible to Phytophthora cinnamomi dieback,[10] but in a recent study the pathogen was found to have no direct impact on the species. As a result of this finding, together with the low percentage of populations infested or facing imminent infestation, the species was classed as having a very low extinction risk.[11]

With fairly small populations and a narrow distribution, B. aculeata is considered rare, but is not currently classed as endangered because at least some populations are thought not to be under immediate threat. The Department of Environment and Conservation classes it as "Priority Two - Poorly Known" flora.[12]

Cultivation

Banksia aculeata grows slowly, taking five to six years to flower from seed.[13] The flowers are brightly coloured but have a short life and are obscured by the foliage, which is quite prickly. However both the new foliage and the infructescence are considered attractive.[14]

This species can grow in a range of soil types so long as they provide good drainage. The nominal pH range is from 5.5 to 6.5. It prefers full sun, although it will grow in partly shaded situations but produce fewer flowers. It will tolerate light pruning.[13][14]

References

  1. 1 2 George, Alex (1999). "Banksia". In Wilson, Annette (ed.). Flora of Australia 17B. CSIRO Publishing / Australian Biological Resources Study. pp. 175–251. ISBN 0-643-06454-0.
  2. 1 2 3 4 George, Alex S. (1981). "The Genus Banksia L.f. (Proteaceae)". Nuytsia 3 (3): 239–473 [386–89]. ISSN 0085-4417.
  3. 1 2 Thiele, Kevin; Ladiges, Pauline Y. (1996). "A cladistic analysis of Banksia (Proteaceae)". Australian Systematic Botany 9 (5): 661–733. doi:10.1071/SB9960661.
  4. ↑ 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 (4): 321–342. doi:10.1071/SB97026.
  5. ↑ Mast, Austin R.; Givnish, Thomas J. (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. PMID 21665734. Retrieved 2006-07-02.
  6. ↑ Mast, Austin R.; Jones, Eric H.; Havery, Shawn P. (2005). "An assessment of old and new DNA sequence evidence for the paraphyly of Banksia with respect to Dryandra (Proteaceae)". Australian Systematic Botany (CSIRO Publishing / Australian Systematic Botany Society) 18 (1): 75–88. doi:10.1071/SB04015.
  7. ↑ Mast, Austin R.; Thiele, Kevin (2007). "The transfer of Dryandra R.Br. to Banksia L.f. (Proteaceae)". Australian Systematic Botany 20: 63–71. doi:10.1071/SB06016.
  8. 1 2 Taylor, Anne; Hopper, Stephen (1988). The Banksia Atlas (Australian Flora and Fauna Series Number 8). Canberra, Australian Capital Territory: Australian Government Publishing Service. pp. 48–49. ISBN 0-644-07124-9.
  9. ↑ Lamont, Byron B.; Markey, Adrienne (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.
  10. ↑ "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.
  11. ↑ Barrett, Sarah; Shearer, B. L.; Crane, C. E.; Cochrane, A. (2008). "An extinction-risk assessment tool for flora threatened by Phytophthora cinnamomi". Australian Journal of Botany 56 (6): 477–486. doi:10.1071/BT07213.
  12. ↑ "Banksia aculeata A.S.George". FloraBase. Department of Environment and Conservation, Government of Western Australia.
  13. 1 2 Collins, Kevin; Collins, Kathy; George, Alex (2008). Banksias. Melbourne: Bloomings Books Pty Ltd. ISBN 978-1-876473-68-6.
  14. 1 2 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.

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