HUYSMANS, SUZY1*, STEVEN DESSEIN1, STEVEN JANSEN1, FREDERIC LENS1, STEFAN VINCKIER1, FREDERIC PIESSCHAERT1, PETRA DE BLOCK2, KOEN ES2, MARCEL VERHAEGEN2, PIET STOFFELEN2, ELMAR ROBBRECHT2, and ERIK SMETS1. 1Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U.Leuven, Kasteelpark Arenberg 31, B-3001 Leuven, BELGIUM; 2National Botanic Garden of Belgium, Domein van Bouchout, B-1860 Meise, BELGIUM. - Pollen morphological variation in Rubiaceae: a portrait.
The predominantly tropical family Rubiaceae is with ca. 13.000 species
one of the largest families of angiosperms. Contrary to some other
huge families, the pollen morphological variation within the family is
impressive. Although the tricolporate pollen type dominates by far, a
number of tribes (e.g., Psychotrieae, Spermacoceae, Sabiceeae) are
highly eurypalynous. In many cases, the pollen morphological diversity
observed has a high systematic value. Pollen grains are mostly
dispersed as monads, but a small number of genera are characterized by
permanent tetrads; polyads occur in a single genus, Massularia. Pollen
size ranges from 6 to 120 µm; shape varies from oblate to prolate, but
is most often subspheroidal. Number of apertures ranges from 0 to 30.
They are generally compound, i.e. made up by different apertures one
above the other. The sexine pattern is also variable, including
psilate, perforate, microreticulate to reticulate, and rugulate
patterns. Supratectal elements are mostly absent, but if present they
show a wide array of morphological variation. Orbicules are often
present and can be spherical, doughnut-shaped, irregularly folded or
spinulate. The results presented are a summary of the pollen
morphological observations achieved in the last 7 years at the
Laboratory of Plant Systematics and the National Botanic Garden of
Belgium. We aim to explore the pollen and orbicule morphological
diversity of the Rubiaceae in order to assess the systematic value of
the respective characters. The database of all genera investigated
with reference to our papers will be available soon at
http://www.kuleuven.ac.be/bio/sys/pollen.
Key words: orbicules, pollen morphology, Rubiaceae, systematics