Proteaceae Floral Crops: Cultivar Development and Underexploited Uses*

Abstract

The Proteaceae apparently originated on the southern supercontinent Gondwana long before it divided and began drifting apart during the Mesozoic era, accounting for the presence of the Proteaceae on all of the southern continents (Brits 1984a). The Protea family comprises about 1400 species in over 60 genera, of which over 800 species in 45 genera are from Australia. Africa claims about 400 species, including 330 species in 14 genera from the western Cape. About 90 species occur in Central and South America, 80 on islands east of New Guinea, and 45 in New Caledonia. Madagascar, New Guinea, New Zealand, and Southeast Asia host small numbers of species (Rebelo 1995). Proteas are neither herbaceous nor annual, and they are always woody. Their structural habit is variable from groundcover forms with creeping stems, and those with underground stems, to vertical to spreading shrubs, to tree forms. The leaves are generally large, lignified, hard, and leathery. A mature leaf will generally snap rather than fold when bent. The leaf anatomy is specially adapted for water conservation and drought resistance. These characteristics and the high leaf carbon to nitrogen ratio render the leaves indigestible to most insect pests (Rebelo 1995), accounting for the relatively pest-free status of most commercial protea plantings. The distribution of the family is linked to the occurrence of soils that are extremely deficient in plant nutrients (Brits 1984a). An accommodating characteristic of the family is the presence of proteoid roots. These are dense clusters of hairy rootlets that form a 2–5 cm thick mat at the soil surface which enhances nutrient uptake from the nutrient-sparse soils on which the Proteaceae evolved. All species examined so far, in at least ten genera, possess proteoid roots (Lamont 1986). The capitulum, in which the flowers are borne on a flat or pointed receptacle, is the most common type of flowerhead. Involucral bracts surround the receptacle and may be prominent, as in Protea, or inconspicuous, as in Leucospermum. Involucral bracts in Leucadendron are also inconspicuous, but the floral bracts of female plants are large and develop into woody cones. An important taxonomic feature of the family is that its flowers do not have separate sepals and petals. The perianth is made up of a single set of four segments called tepals. As a bud opens, the perianth segments curl back to expose the style which extends from the superior ovary to the stigma. In some species, small floral nectaries at the base of the ovary secrete nectar to attract pollinators (Rebelo 1995). Another adaptation of evolution that has become important in the utilization of Leucospermum and Protea as cutflowers is bird pollination. The large, usually solitary, terminal flowers of these genera, and their predominant colors of creamy white, and blends of yellow, orange, and red, colors birds are attracted to, are probably adaptations to pollination by the Cape Sugarbird, Promerops cafer, and other nectar eating native birds. This is thought to be the prime reason why the South African species, and perhaps particularly Leucospermum and Protea, are the most attractive of the family and have excellent potential as cutflowers (Brits 1984a). The floral biology of proteas is protandrous, with anthesis occurring prior to the stigma becoming receptive; a mechanism to help insure cross pollination. Most Protea seem incapable of self-pollination, although certain Leucospermum and Serruria species will produce seed when self pollinated. There are four types of pollinators, or pollen delivery; rodents, birds, insects, and wind. The flowerheads of certain Leucospermum and Protea species are visited by several species of gerbils, mice, rats, and shrews. Many Leucospermum, Mimetes, and Protea species are pollinated by birds. Since birds do not rely on smell, birdpollinated species have little if any scent. The small species of Leucospermum and Protea are pollinated by bees and wasps and a few other insects; Leucadendron are pollinated by several beetle species, and most small-flowered genera are visited by a number of beetle, fly, and wasp species. Ten Leucadendron species are the only wind-pollinated proteas in southern Africa (Rebelo 1995).

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