Underground starch storage in Erica species of the Cape Floristic Region – differences between seeders and resprouters

Abstract

Concentrations of starch in roots of seeder species of Erica from the Cape Floristic Region, South Africa were found to be considerably less than in resprouters. Shoot starch was highly variable but mean values were similar in both seeder and resprouter species of Erica. Three distinct patterns of starch storage in roots were recognized. All seeder species fell within definitions of Categories 1 (narrow major and minor parenchymatous rays, one to two cells wide with no inter-ray storage) or 2 (thick major rays up to seven cells wide and thin minor rays with small amounts of inter-ray storage) whereas resprouter species were consistently within Categories 2 or 3 (broad major and minor rays, up to eight cells wide and conspicuous inter-ray starch storage). Results are discussed in light of similar studies of the related Epacridaceae. ‘Mixed’ species (i.e. with seeder or resprouter individuals present, often in distinct populations) were always classified as belonging to Category 2. Studies of populations of three ‘mixed’ species confirmed that seeder forms had consistently lower amounts of root starch than resprouters. Rays of xylem parenchyma were the main sites for starch storage in roots of both seeders and resprouters and greater proportions of cross-sectional area of roots were consistently devoted to such storage tissues in resprouter forms of the three ‘mixed’ species. Analyses of a number of seeder and resprouter Erica coccinea populations showed that differences in amounts of realised and potential root starch storage are best explained by the effect of regeneration behaviour rather than by among-population variability.