User:Hesperian/Notes/Anatomy of Banksia

Lead

Habit

always woody. highly variable: tree, shrub, prostrate shrub

seminuda to 30m.

some have trunks 1 m in diameter - integrifolia, seminuda, marginata

shrubs.

lignotuberous shrubs with many stems

prostrate shrubs-underground stems

Bark and indumentum

lenticels

fissuring

indumentum

Leaves

cotyledons highly variable. - sclerophylly. margin, lamina, colour, felting, venation

dorsiventral - stomata on underside

juvenile leaves may differ

In most Banksia species, each individual flower is subtended by a floral bract, though these are reduced to scales less than a millimetre in diameter.

Flowers

The flowers are fairly typical of Proteaceae. They are tetramerous (flower parts occur in fours), and consist of a tubular perianth, four stamens, and a single pistil.

The perianth is an elongate tube formed from the four united tepals. It is somewhat swollen at the base, where the ovary is situated; and then narrow and tapering for most of its length. At the tip of the perianth is an enclosure, termed the limb, which is oblong in most species, but may be linear or even drawn into a filamentous awn. It may also be turned upwards or downwards, making it the only part of the perianth that is not always actinomorphic (rotationally symmetrical). It is glabrous in some species, hairy in others, and in some it is topped with a few long thin hairs.

The four stamens are located within the limb. They have very short filaments, and are attached one to each tepal.

The pistil

hypogynous scales?

consists of three parts, which according to longstanding

When in bud, the four tepals are fused together into a long tubular perianth. This is somewhat swollen at the base, where the ovary is contained; then narrow and often tapering through the middle part, termed the claw in Proteaceae terminology; and finally ending in a limb, which is often thickened. For the most part the perianth is actinomorphic (rotationally symmetrical) in bud, but the limb may be slightly bent forward.

The four stamens are situated within the limb, one on each tepal. They are

, but closed cup at the top, and the filaments of the four stamens are fused to the tepals, in such a way that the anthers are enclosed within the cup. The pistil initially passes along the inside of the perianth tube, so that the stigma too is enclosed within the cup. As the flower develops, the pistil grows rapidly. Since the stigma is trapped, the style must bend in order to elongate, and eventually it bends so far that it splits the perianth along one seam. The style continues to grow until anthesis, when the nectaries begin to produce nectar. At this time, the perianth splits into its component tepals, the cup splits apart, and the pistil is released to spring more or less upright.

Just before anthesis, the anthers release their pollen, depositing it onto the stigma, which in many cases has an enlarged fleshy area specifically for the deposition of its own pollen. Nectar-feeders are unlikely to come into contact with the anthers themselves, but can hardly avoid contacting the stigma; thus the stigma functions as a pollen-presenter, ensuring that nectar-feeders act as pollinators. The down side of this pollination strategy is that the probability of self-fertilisation is greatly increased; many Proteaceae counter this with strategies such as protandry, self-incompatibility, or preferential abortion of selfed seed.

four-partite; four tepals united into perianth. cup at top, with very short anthers inside.
pistil inside perianth. modified style-end (pollen-presenter). style-end trapped inside perianth cup.
Style elongates but perianth doesn't; style must bend. Breaks through a seam where tepals are united. eventually breaks free from the perianth cup.

flower colour

Inflorescences

Characteristic of Grevilleoideae, flowers occur in pairs arising from the axil of a common bract. Common bracts are typically less than 2 mm in diameter, and are usually truncate or conical. Since the flowers are sessile, each flower's floral and common bracts occur very close together, so that the floral structure that pairs the flowers is typically no more than a few millimetres in size. These structures are packed together in a regular grid, with each diamond-shaped common bract surrounded by the floral bracts of itself and its neighbouring common bracts. In some species with low flower density, the flowers develop without crowding each other, and the arrangement pattern may persist for the life of the inflorescence. In others, the developing flowers crowd each other out of position, obscuring the arrangement pattern, or at least disrupting one or more lines of symmetry.

Flowers occur in either spikes or heads. In the case of spikes, the unit inflorescences are arranged around, and at right angles to, a woody axis termed a rachis. These range in size from up to 40 centimetres long, with 6000 flowers, in B. grandis, down to a few centimetres, with a few hundred flowers, in Banksia candolleana. In the Isostylis group, the spike is even further reduced, to an ovoid ball about a centimetre high; in these species the inflorescence has the appearance of a flower head, rather than a spike, and may contain fewer than a hundred flowers. True flower heads occur only in the Dryandra group, in which flower arise vertically from a flat, concave or convex plate termed a receptacle. These typically hold around a hundred flowers, though in some species there may be as few as 20, and in others they may be more than 200.

Various terms have been proposed to resolve the ambiguity caused by the fact that both flower pairs and entire flower spikes or heads may be correctly termed inflorescences: the former have sometimes been termed unit inflorescences or uninflorescences, whereas the latter have been termed synflorescences or conflorescences.

upright, pendulous order of opening - acropetal v basipetal always terminal, but may be terminal to a branch or to a short lateral branchlet. May be subtended.

honeypots

involucral bracts

Infructescences

retention/loss of old flowers

limit to number of follicles that can develop

Follicles

beaked split versus unbeaked split

two seeds

seed-separator - reflexed wings.

how far exserted

Seeds

triangular, winged.

Roots

Cluster roots

B prionotes - dimorphic: cluster on laterals + tap