Pollen of the Spermacoce (Rubiaceae) species from the Northern Territory of Australia: morphology and taxonomic significance
S. Dessein A D , R. Harwood B , E. Smets A and E. Robbrecht CA Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U.Leuven, Kasteelpark Arenberg 31, B-3001 Leuven, Belgium.
B Northern Territory Herbarium, PO Box 496, Palmerston, NT 0831, Australia.
C National Botanic Garden of Belgium, Domein van Bouchout, B-1860 Meise, Belgium.
D Corresponding author. Email: steven.dessein@bio.kuleuven.ac.be
Australian Systematic Botany 18(4) 367-382 https://doi.org/10.1071/SB03025
Submitted: 10 September 2003 Accepted: 6 April 2005 Published: 31 August 2005
Abstract
Complementary to the revision of the genus Spermacoce in the Northern Territory of Australia, pollen morphology of 48 of the 53 native Spermacoce species from the Northern Territory has been investigated by scanning electron and light microscopy. There is considerable variation for most diagnostic pollen characters. The average equatorial diameter (E) ranges from 10.5 to 41.7 µm. Grains are invariably colporate with the apertures situated at the equator (being zonocolporate). The number of apertures varies from 3 to 17. The endoaperture is generally an endocingulum, often with a secondary thinning at the ectocolpus; one species has endocolpi. The sexine is usually perforate, but psilate, foveolate, and (micro)reticulate patterns were also found. Supratectal elements are present as granules or microspines scattered over the whole surface or confined to a region around the ectoapertures. The inner nexine surface is granular, often with irregular grooves (endocracks).
The pollen morphological variation observed allows the distinction of four pollen types. Three of these types are not yet recorded in other palynological studies of Spermacoce. Pollen characters are often useful to delimit species and groups of related species.
Acknowledgments
We thank Marcel Verhaegen from the National Botanic Garden of Belgium for taking SEMs from the pollen grains, and Suzy Huysmans and an anonymous reviewer for the valuable comments on the first drafts of this manuscript. Steven Dessein is a postdoctoral fellow of the Fund for Scientific Research, Flanders (FWO-Vlaanderen). Financial support for this study was provided by project OT/01/25 from the Research Fund of the K.U.Leuven.
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