• Korean Journal of Plant Taxonomy
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• v.48 no.1
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• pp.9-23
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• 2018

The distribution of orbicules was investigated for eleven taxa of six genera in Lamiaceae and four taxa of three genera in Verbenaceae using scanning electron microscopy. A literature survey to evaluate the phylogenetic potential of the orbicules and their possible correlations with tapetum types was also conducted. The orbicules are consistently absent in all investigated taxa of Lamiaceae, while small orbicules of an average size of less than $1{\mu}m$ are densely distributed in Verbenaceae. In fact, orbicules appear consistently in 123 of 150 angiosperm families when investigated in at least one species. Thus, the distribution patterns of orbicules could be a useful diagnostic character in angiosperms. In addition, orbicules occur in 84% taxa of the secretory tapetum type, while they are commonly absent in the amoeboid tapetum type (ca. 80%). The presence of orbicules may be correlated with the secretory tapetum type. However, the study of orbicules is restricted in 150 families and the tapetum type within these families can be applied for 92 families out of a total of 416 angiosperm families. Thus, further investigation of orbicules is necessary in extended taxa to address the questions pertaining to orbicules.