In this article we will discuss about:- 1. General Features of the Proteaceae 2. Floral Range in the Proteaceae 3. Divisions 4. Position and Affinity 5. Number and Distribution 6. Commonly Occurring Plants 7. Economic Aspects.
General Features of the Proteaceae:
Habit – Shrubs or trees.
Leaves – Alternate, opposite or whorled, simple, exstipulate.
Inflorescence – Showy bracteate heads, racemes or spikes.
Flowers – Bisexual, irregular or regular, hypogynous.
Perianth – Tetramerous, petaloid, coloured, valvate, variously split when open.
Androecium – Stamens equal in number, opposite to perianth-segments and adnate to them; anthers 2-celled, free.
Gynoecium – Carpel 1; ovary superior; ovules 1 or more; placentation parietal.
Seeds – Winged; endosperm absent.
Floral Range in the Proteaceae:
The various types of inflorescence occurring in the family have been derived from panicle by reduction and condensation or simplification.
The flowers are borne in pairs (Grevilleoideae) or are solitary (Persoonioideae). Although they are bisexual, unisexual flowers are seen in Leucadendron. They are usually regular, but irregular in Lomatia and other genera.
Out of 4 stamens, 2 are 2-celled and the rest 1-celled: this condition is noticed in some species of Conospermum and Synaphea. In Symphyonema, the stamens are free from the tepals.
At the base of the ovary, one may find various forms of nectariferous scales. These structures, according to Venkata Rao (1962), consist of three free lobes alternating with perianth segments. However, Kausik (1938) and Haber (1959) suggested that these organs represent reduced inner perianth members.
Divisions of the Proteaceae:
The Proteaceae is divided into two subfamilies:
Subfamily I:
Grevilleoideae. Flowers in pairs borne on apparent racemes or spikes. Ovules many, sometimes 2. Fruit a several seeded follicle. Examples: Banksia, Hakea, Lomatia, etc.
Subfamily II:
Persoonioideae. Flowers single at axil of bracts. Ovules 1, 2 or few. Fruit a 1-seeded drupe. Examples: Leucadendron, Persoonia, Protea, etc.
Position and Affinity of the Proteaceae:
Basically, the Proteaceae is not a primitive taxon. But there seems to be no agreement among botanists as to its proper position. It formed the 15th series of Engler’s Archichlamydeae, near the Urticales and before the Santalales. Accepting Engler’s opinion of primitiveness of the order, Hallier derived it from the Proberberideae. Bessey cast doubt on the relationship of the Proteaceae which was placed in the Sapindales.
Rendle also pointed out that it is difficult to associate the order with other taxa. Lawrence stated that the order is not closely related to any other group. Hutchinson regarded it to be a terminal group originating from stocks ancestral to the Thymelaeaceae.
As the Proteaceae bears close affinity to the Thymelaeaceae, Mitra (1974) imparted the position of the Proteales after the Myrtales and before the Santalales. That the Proteaceae is fairly advanced has been revealed by the studies of Haber (1959); he proved that the occurrence of four types of ovule (anatropous, basal, orthotropous, pendulous), reduction of petals into nectariferous scales and occasional zygomorphy with orninthophilous flowers are signs of advancement.
In its inflorescence, the family “often mimics both Asteraceae (Compositae) and Pinaceae, in Protea and Leucadendron respectively, while the superficial resemblance of its fruits with those of some Fabaceae (Papilionaceae) has caused some authors to suggest an affinity with the last mentioned family”.
Number and Distribution of the Proteaceae:
A large family of 62 genera and over 1,000 species, the Proteaceae is highly developed in the drier regions of southern hemisphere, mainly Australia and South Africa.
Commonly Occurring Plants of the Proteaceae:
Australian Silky Oak (Grevillea robusta A. Cunn. ex R. Br.), often grown in gardens, parks and roadsides, is a dominant tree of Mount Abu, Rajasthan.
Hakea sericea Schrad is a conifer-like plant, bearing acicular leaves and axillary clusters of white or pinkish flowers.
Economic Aspects of the Proteaceae:
The Proteaceae furnishes us with many beautiful ornamentals like Embothrium coccineum, Grevillea robusta, Hakea laurina, Leucadendron argenteum, Protea mellifera and Telopea speciosissima. Faurea macnaughtonii and Knightia excelsa yield good timber. The fruits of Gevuina avellana and Macadamia ternifolia are edible. The bark of Leucospermum conocarpodendron is used for tanning leather.
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