Abstract
Pollen of 57 species of Syzygium from SE Asia were surveyed by SEM. The grains are all ± triangular in polar view, uniformly small (mean diameter 10.4 μm) with few surface sculpturing features. All species examined exhibit a distinct apocolpium and, usually, apocolpial field. The presence of an apocolpial field cannot be linked to any known taxonomic grouping within the genus. It does not appear possible to distinguish the species of Syzygium on the basis of features of the pollen visible under SEM, though section Jambosa tends to have larger pollen with a proportionally larger apocolpium than species not in that section. Estimates for the number of pollen grains per stamen in species with larger pollen grains (± section Jambosa) are 5× as great as for other species in the genus. TEM preparations showed the pollen surface to bear small supratectal processes and to be covered with pollenkit. The foot layer is well developed and more or less of the same thickness as the tectum. The columellae are of variable width and the endexine c. 0.05 μm thick. Various features of flower size are found to be positively correlated to pollen size. As large pollen grains are linked to large staminal numbers and large stamens (long filaments and large anthers) it is suggested that investigation of the breeding biology of section Jambosa is required.
Highlights
The Myrtaceae are a moderately sized, mostly southern hemisphere family containing between 132 and 150 genera and somewhere between 3,675 and 3,900 species (Schmid, 1980; Johnson et al, 1988; Kochummen, 1995; Lemmens, 1995; Mabberley, 1997)
Though his proposed division is based on a substantial sub-sample of Syzygium and is the product of phylogenetic and phenetic analyses of many morphological characters it is clear from his paper that there is a dearth of information on pollen morphology
This study focuses on the pollen morphology of Syzygium in Thailand
Summary
The Myrtaceae are a moderately sized, mostly southern hemisphere family containing between 132 and 150 genera and somewhere between 3,675 and 3,900 species (Schmid, 1980; Johnson et al, 1988; Kochummen, 1995; Lemmens, 1995; Mabberley, 1997). Despite its modest size the family is an extremely important component of the flora of the southern hemisphere. Tree species in the family dominate the forests of Australia and there are many taxa which form important components of the forests of Southeast Asia, South America and the islands of Oceania (Johnson & Briggs, 1981). In many members of the Myrtaceae the stamens perform the dual functions of pollen production and dispersal and the function of pollinator attraction through the formation of brush-blossom inflorescences (Johnson & Briggs, 1981). The widespread and species-rich genus Syzygium is a good example of this pollination syndrome
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