Abstract
The pollen morphology and distribution of orbicules were investigated in ten species of the genus Coptosapelta (Rubiaceae) using light, scanning electron and transmission electron microscopy. In general, Coptosapelta pollen is three- to five-pororate and suboblate to oblate-spheroidal. The sexine ornamentation varies from psilate to reticulate, and the pollen-wall stratification lacks columellae. ‘Droplets’ are observed on the inner nexine surface. Distinct orbicules are found in five species. Orbicules are often lobed and appear to be aggregated and embedded in the tapetal remnants of the locule wall. Ultrastructurally, a single, flattened core is frequently observed. Coptosapelta has a unique pollen type within Rubiaceae and does not resemble possibly related genera. Pollen characteristics provide additional evidence supporting earlier findings that Coptosapelta represents an isolated lineage in Rubiaceae.
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Acknowledgements
We are grateful to Steven Jansen for critical review and constructive comments on the paper. We are also grateful to the keepers of bm, br, k, l, ny and p for the loan of herbarium material and their approval to extract material. We thank Marcel Verhaegen for making the SEM pictures and Prof. Billen (Laboratory for Entomology, Catholic University of Leuven) for access to the TEM. This research is supported by a grant from the research council of the K.U.Leuven (OT/01/25) and by a grant from the Fund for Scientific Research – Flanders (1.5.069.02).
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Verellen, J., Smets, E. & Huysmans, S. The remarkable genus Coptosapelta (Rubiaceae): pollen and orbicule morphology and systematic implications. J Plant Res 117, 57–68 (2004). https://doi.org/10.1007/s10265-003-0128-0
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DOI: https://doi.org/10.1007/s10265-003-0128-0