Relationships between fire response, morphology, root anatomy and starch distribution in south-west Australian Epacridaceae

Selected epacrids (92 species in 15 genera) were examined with respect to fire response type, morphology, root anatomy and starch storage. Seeders, 75 % of the species investigated, possessed a single main stem and a small root system with lateral roots which in most cases did not spread beyond the shoot canopy. Resprouter species were generally multi-stemmed with large lignotuberous root stocks. Certain seeder and resprouter species were intermediate in form and showed small root systems and basally branched main stems. Amounts of starch in roots of seeders (1.9+/-0.5 mg starch g d. wt per root) were much less than in resprouters (14.1+/-3.3) whereas amounts in shoots were similar (1.9+/-0.5 and 16+/-0.6 mg starch g d. wt per shoot, respectively). Starch storage in roots was mostly confined to rays of xylem parenchyma and inter-ray xylem parenchyma and the greater storage capacity of resprouters was generally due to broader rays. Growth zones in root xylem ranged from clear, verifiable annual rings, as in many seeder species, to indistinct growth zones, typical of many resprouter species. Shoot:root dry weight ratios were higher in seeders than resprouters. The study suggests that speciation within the Epacridaceae into seeder and resprouter forms involved divergent differentiation in terms of morphology, shoot:root dry weight ratio root storage of starch. (C) 1996 Annals of Botany Company