Banksia
Banksia is a genus of around 170 species in the plant family Proteaceae. These Australian wildflowers and popular garden plants are easily recognised by their characteristic flower spikes and fruiting "cones" and heads. Banksias range in size from prostrate woody shrubs to trees up to 30 metres (100 ft) tall. They are found in a wide variety of landscapes: sclerophyll forest, (occasionally) rainforest, shrubland, and some more arid landscapes, though not in Australia's deserts.
Heavy producers of nectar, banksias are a vital part of the food chain in the Australian bush. They are an important food source for all sorts of nectarivorous animals, including birds, bats, rats, possums, stingless bees and a host of invertebrates. Further, they are of economic importance to Australia's nursery and cut flower industries. However, these plants are threatened by a number of processes including land clearing, frequent burning and disease, and a number of species are rare and endangered.
Banksias grow as trees or woody shrubs. Trees of the largest species, B. integrifolia (coast banksia) and B. seminuda (river banksia), often grow over 15 metres tall, some even grow to standing 30 metres tall.[1] Banksia species that grow as shrubs are usually erect, but there are several species that are prostrate, with branches that grow on or below the soil.
The leaves of Banksia vary greatly between species. Sizes vary from the narrow, 1–1½ centimetre long needle-like leaves of B. ericifolia (heath-leaved banksia), to the very large leaves of B. grandis (bull banksia), which may be up to 45 centimetres long. The leaves of most species have serrated edges, but a few, such as B. integrifolia, do not. Leaves are usually arranged along the branches in irregular spirals, but in some species they are crowded together in whorls. Many species have differing juvenile and adult leaves (e.g., Banksia integrifolia has large serrated juvenile leaves).
The flowers are arranged in flower spikes or capitate flower heads.[2] The character most commonly associated with Banksia is the flower spike, an elongated inflorescence consisting of a woody axis covered in tightly packed pairs of flowers attached at right angles. A single flower spike generally contains hundreds or even thousands of flowers; the most recorded is around 6000 on inflorescences of B. grandis. Not all Banksia have an elongate flower spike, however: the members of the small Isostylis complex have long been recognised as Banksias in which the flower spike has been reduced to a head; and recently the large genus Dryandra has been found to have arisen from within the ranks of Banksia, and sunk into it as B. ser. Dryandra. They similarly have capitate flower heads rather than spikes.
Banksia flowers are usually a shade of yellow, but orange, red, pink and even violet flowers also occur. The colour of the flowers is determined by the colour of the perianth parts and often the style. The style is much longer than the perianth, and is initially trapped by the upper perianth parts. These are gradually released over a period of days, either from top to bottom or from bottom to top. When the styles and perianth parts are different colours, the visual effect is of a colour change sweeping along the spike. This can be most spectacular in B. prionotes (acorn banksia) and related species, as the white inflorescence in bud becomes a brilliant orange. In most cases, the individual flowers are tall, thin saccate (sack-shaped) in shape.
