- Macadamia tetraphylla, commonly known as rough-shelled macadamia or prickly macadamia, is a tree native to southeastern Queensland and northeastern New South Wales, Australia. This species is one of the few edible members of the family Proteaceae and is commercially cultivated for its valuable nuts.
- The tree typically grows to heights of 15-20 meters in cultivation, though it can reach greater heights in natural settings. It develops a dense, rounded canopy with dark green foliage. The trunk is straight with smooth, gray bark that becomes more textured with age. The tree exhibits strong apical dominance in its early growth stages.
- The leaves are arranged in whorls of four (tetraphylla meaning “four leaves”), a characteristic that distinguishes it from other macadamia species. Individual leaves are elliptical to lanceolate, 10-30 cm long, with sharply serrated margins containing prominent spiny teeth. Young leaves often show a bronze or reddish coloration before maturing to dark green.
- The inflorescences are long, pendant racemes, typically 15-30 cm in length, bearing numerous small, cream to pink flowers. These racemes develop in the leaf axils and can contain hundreds of individual flowers. Flowering usually occurs in late winter to early spring, though timing can vary with climate conditions.
- The fruit is a follicle containing a single seed (the macadamia nut). The outer husk is green, becoming brown and splitting when mature to reveal the rough-shelled nut inside. The shell is characterized by its rough, pebbled surface texture, distinguishing it from the smooth-shelled M. integrifolia. The kernel inside is cream-colored and highly prized for its rich, buttery flavor.
- M. tetraphylla is adapted to subtropical climates with moderate rainfall (1000-2000mm annually) and temperatures generally between 15-30°C. It can tolerate light frosts but is damaged by prolonged freezing temperatures. The species performs best in deep, well-drained soils with good organic matter content and pH between 5.5-6.5.
- Growth and development patterns show strong seasonal variation. Major growth flushes typically occur in spring and summer, with flowering preceding new vegetative growth. Trees begin bearing commercially viable crops at 5-7 years of age, with production increasing for several years thereafter.
- Cultivation practices focus on canopy management and maintaining optimal growing conditions. Trees require regular pruning to maintain manageable size and encourage productive growth. Irrigation is often necessary during dry periods, particularly during nut development.
- The species demonstrates good adaptation to various soil types but requires good drainage and adequate depth for root development. Root health is crucial for productivity, with trees being sensitive to both waterlogging and drought stress. Mycorrhizal associations play an important role in nutrient uptake.
- Harvesting occurs when nuts naturally fall to the ground, typically over several months. The nuts must be collected promptly to maintain quality and prevent spoilage. Post-harvest processing involves removing the outer husk, drying the in-shell nuts to proper moisture content, and cracking to obtain the kernels.
- Disease susceptibility includes various fungal pathogens affecting roots, trunk, and foliage. Major pests include various borers, scales, and macadamia nut borers. Integrated pest management strategies are typically employed in commercial production.
- Breeding programs often utilize M. tetraphylla in crosses with M. integrifolia to develop improved varieties combining desirable traits from both species. Key breeding objectives include improved yield, disease resistance, and kernel quality characteristics.
- The nuts are highly nutritious, containing approximately 75% oil, primarily monounsaturated fats, along with protein, fiber, and various minerals. The oil composition contributes to both the distinctive flavor and the long shelf life of properly processed nuts.
- Commercial production is primarily focused in Australia, Hawaii, and various other subtropical regions. The species is often grown alongside M. integrifolia, though pure M. tetraphylla orchards are less common commercially due to generally lower yields and harder shells.
- Research continues into various aspects of production, including improved cultivation methods, disease management, and processing technologies. Understanding of environmental interactions and stress responses helps inform management practices.
- Conservation of genetic diversity remains important, particularly given the species’ restricted natural distribution. Wild populations represent valuable genetic resources for breeding programs and adaptation to changing environmental conditions.
- The species faces various challenges including climate change impacts, disease pressures, and production costs. However, strong market demand and increasing interest in tree crop diversity suggest continuing importance in global nut production.
- Traditional knowledge from Aboriginal peoples regarding the species’ use and management provides valuable insights for modern cultivation practices. The species continues to hold cultural significance in its native range.
