| Holly-leaved Banksia | |
|---|---|
| Scientific classification | |
| Kingdom: | Plantae |
| (unranked): | Angiosperms |
| (unranked): | Eudicots |
| Order: | Proteales |
| Family: | Proteaceae |
| Genus: | Banksia |
| Subgenus: | Banksia subg. Isostylis |
| Species: | B. ilicifolia |
| Binomial name | |
| Banksia ilicifolia R.Br. |
|
| Synonyms | |
|
Sirmuellera ilicifolia |
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Banksia ilicifolia, commonly known as Holly-leaved Banksia, is a tree in the plant Proteaceae family. Endemic to southwest Western Australia, it belongs to Banksia subg. Isostylis, a subgenus of three closely related Banksia species with inflorescences that are dome-shaped heads rather than characteristic Banksia flower spikes. It is generally encountered as a tree up to 10 m (35 ft) high, with prickly green foliage and yellow and red-tinged flowers. Both the scientific and common names arises from the similarity of its foliage to that of the English holly Ilex.
Although Banksia ilicifolia is variable in habit, with low coastal shrubby forms on the south coast near Albany, there are no recognised varieties as such. Unlike its close relatives, Banksia ilicifolia regenerates after bushfire by regrowing from epicormic buds under its bark. It is rarely cultivated.
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Banksia ilicifolia is a fairly variable species. It usually grows as an erect tree up to 10 m (30 ft) in height, but some populations along the south coast consist of small trees or even spreading shrubs.[1]
It has a stout trunk up to 50 cm (20 in) in diameter, and thick, fibrous, grey bark. Resembling those of holly, its leaves are a dark shiny green colour, and variously obovate, elliptic, truncate or undulate in shape, and 3–10 cm (1–4 in) long. The leaf edges are generally serrated and quite prickly. The leaves sit atop petioles 0.3–1 cm in length. The upper and undersurface of the leaves are initially covered in fine hairs but become smooth with maturity. Appearing from late winter to early summer, the inflorescences are dome-shaped flower heads rather than spikes as many other banksias. They measure 7–9 cm (2.8–3.6 in) in diameter, and bear 60 to 100 individual flowers. The inflorescences pass through three colour phases, being initially yellow, then pink, then finally red, before falling away from the head. Flowering is followed by the appearance of one to three follicles, which remain embedded in the woody base of the flower head. Each bears one or two seeds.[2]
In the Margaret River region, it has been confused with Banksia sessilis var. cordata as both have prickly foliage and domed flowerheads, however the former grows on deep sand while the latter grows on grey sand over limestone ridges. The embedded follicles of B. ilicifolia compared with the loose ones of B. sessilis are another distinguishing feature.[3]
Because of its dome-shaped flower heads, the Holly-leaved Banksia is placed in the subgenus Banksia subg. Isostylis. It is the only common member of that subgenus; the two other species are rare and threatened, and are protected under the Environment Protection and Biodiversity Conservation Act 1999.
The Holly-leaved Banksia was first collected by Robert Brown in 1801 or 1802 at King George Sound, and published by him in 1810. The shrubby, coastal ecotype was incorrectly published as a separate species Banksia aquifolium by John Lindley in his 1840 A Sketch of the Vegetation of the Swan River Colony, but this has since been corrected to a taxonomic synonym of B. ilicifolia. No subspecies are recognised. The specific name is derived from the Latin words ilex "holly" and folium "leaf", hence "holly-leaved".
George placed B. ilicifolia in subgenus Isostylis because of its dome-shaped flower heads.[1] A 1996 cladistic analysis of the genus by botanists Kevin Thiele and Pauline Ladiges yielded no information about the circumscription of B. subg. Isostylis, nor of the relationships within it, so George's placement of this species was retained in their arrangement.[4] That arrangement was not accepted by George, and was largely discarded by him in his 1999 arrangement. The placement of B. ilicifolia there was unaffected, and can be summarised as follows:[2]
Since 1998, American botanist Austin Mast and co-authors have been publishing results of ongoing cladistic analyses of DNA sequence data for the subtribe Banksiinae, which then comprised genera Banksia and Dryandra. Their analyses suggest a phylogeny that differs greatly from George's taxonomic arrangement. Banksia ilicifolia and B. oligantha form a clade, that is they are each other's closest relative, with Banksia cuneata resolving as the next closest relative, suggesting a monophyletic B. subg. Isostylis; but the clade appears fairly derived (that it, it evolved relatively recently), suggesting that B. subg. Isostylis may not merit subgeneric rank.[5][6][7]
Early in 2007, Mast and Thiele rearranged the genus Banksia by merging Dryandra into it, and published B. subg. Spathulatae for the taxa having spoon-shaped cotyledons; thus B. subg. Banksia was redefined as encompassing taxa lacking 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. ilicifolia is placed in B. subg. Banksia.[8]
A relatively common species, the Holly-leaved Banksia is widely distributed within south west Western Australia. It occurs on sandy soils within 70 km (45 mi) of the coast, from Mount Lesueur to the Cordinup River east of Albany. It especially favours low-lying areas.
Several honeyeater species visit and pollinate Banksia ilicifolia. The Western Spinebill (Acanthorhynchus superciliosus) in particular prefers this species over other banksias.[9]
A field study carried out at Jandakot Airport south of Perth and published in 1988 found that birds and insects overwhelmingly preferred visiting yellow-coloured flowerheads. The species recorded include several species of honeyeater, including the Red Wattlebird (Anthochaera carunculata), Western Wattlebird (A. lunulata), Western Spinebill, Brown Honeyeater (Lichmera indistincta), New Holland Honeyeater (Phylidonyris novaehollandiae), White-cheeked Honeyeater (P. nigra), two species of native bee of the genus Leioproctus, a beetle of the species Liparetrus, and ant species Iridomyrmex conifer. The yellow flowerheads are also the ones that bear the most nectar.[10]
Banksia ilicifolia has been recorded as a source of nectar for the honey possum (Tarsipes rostratus) in winter to early summer (May to December), from field studies in the Scott National Park, replaced by Adenanthos meisneri in the summer.[11]
Banksia ilicifolia is an obligate phreatophyte, that is, it is reliant upon accessing groundwater for its survival; it is more closely tied to the water table unlike the co-occurring Banksia menziesii and Banksia attenuata, and must remain in areas where the depth of the water table is less than 8 m (25 ft) below the surface.[12] Recent falls of the water table on the Swan Coastal Plain from use of the Gnangara Mound aquifer for Perth's water supply as well as years of below average rainfall have seen the population and vigour or Banksia ilicifolia fall considerably (more so than other banksia species) since the mid 1960s.[13]
Banksia ilicifolia has been shown to be highly sensitive to dieback from the soil-borne water mould Phytophthora cinnamomi, like many Western Australian banksias.[14] A study of Banksia attenuata woodland 400 km (250 mi) southeast of Perth across 16 years and following a wave of P. cinnamomi infestation showed that B. ilicifolia populations were present but significantly reduced in diseased areas.[15] Specimens in coastal dune vegetation were reported killed by Armillaria luteobubalina, with mycelial sheaths of the fungus beneath the bark of the root collar.[16]
Banksia ilicifolia 's vulnerability to Phytophthora renders it difficult to grow in areas of summer humidity or high rainfall, such as Australia's east coast. Otherwise, it requires a sunny position and sandy well-drained soil to do well.
Seeds do not require any treatment, and take 22 to 41 days to germinate.[17]