Pollen development in three selected species of Rubiaceae provides ontogenetic evidence for pollen evolution

Yan Feng Kuang*, Lin Yue, Henrik Balslev, Jing Ping Liao

*Corresponding author for this work

Research output: Contribution to journal/Conference contribution in journal/Contribution to newspaperJournal articleResearchpeer-review


Pollen development in Ixora chinensis, Pentas lanceolata, and Spermacoce pusilla was investigated. Simultaneous cytokinesis at meiosis, a persistent epidermis, fibrous thickenings in the endothecium, an ephemeral middle layer, and a secretory tapetum that remains uninucleate were observed in all examined species and constitute a family character in Rubiaceae. The main ontogenetic sequence of sporoderm development is generally centripetal and shows major similarities among the studied species, with slight differences in the timing of specific events. Tapetum degradation starts slightly later in I. chinensis than in P. lanceolata and S. pusilla, while intine formation may be slightly later in S. pusilla than in the other two species. Occurrences of orbicules, white-line-centered endexine lamellae and apertural intine projections were observed in I. chinensis and P. lanceolata but not in S. pusilla. Columellae are well-developed in I. chinensis and P. lanceolata but are simplified in S. pusilla. Carbohydrate reserves in mature pollen grains also vary among these three species. Thickened endexine at the apertural sites and a membranous granular layer are shared by the three species. White-line-centered lamellae might represent a common mechanism for endexine formation in the family. Endexine dilations and thickening occurred in the apertural region represent a common character in the family. The ephemeral membranous granular layer developed beneath the endexine is a very common feature for Rubiaceae. Our study shows that ultrastructural and developmental studies are essential in illustrating micromorphological features of pollen especially these ephemeral characters. Thus, application of palynological ontogenetic data to phylogenetic problems deserves more attention.

Original languageEnglish
Article number104413
JournalReview of Palaeobotany and Palynology
Number of pages16
Publication statusPublished - Jun 2021


  • Endexine
  • Membranous granular layer
  • Sporoderm
  • Ubisch body
  • White lines


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