For phylogenetic mapping of orbicule
distribution data, we used both the APG III topology at order level (APG, 2009) and an updated dahlgrenogram reflecting the relationships between orders in flowering plants (Barthlott, Borsch & Worberg, pers.
types can be described in Rubiaceae (Huysmans et al.,
Another problem that needs to be addressed is the relationship among tapetum type, sexine ornamentation, and orbicule
are resistant to acetolysis and react similarly to the exine with different histochemical stains, thus providing ample evidence for sporopollenin composition of the orbicule
Pollen, tapetum and orbicule
development in Modiolastrum malvifolium (Malvaceae).
The images were transferred to an image-processing software (Macnification, Orbicule
, Inc., Leuven, Belgium), where, with the image of the millimeter ruler present in each, the photographs were calibrated.
Medan, "Pollen, tapetum, and orbicule
development in Colletia paradoxa and Discaria americana (Rhamnaceae)," The Scientific World Journal, vol.
Two possibilities are FailSafe from Phoenix Technologies for PCs and Undercover from Orbicule
Despite these differences, cycad pollen still possesses traits similar to anemophilous germplasm in that: a) it lacks a pollenkitt, a liquid fatty substance on the covering pollen grain that attracts insects in entomophilous angiosperms; b) most have an orbicule
, which is a small acellular structure of sporopollenin (Pacini et al., 1999); and c) it has a multi-layered, thick sporoderm (Pacini, et al., 1999), which enables it to withstand desiccation, possibly as a result of this gymnosperm's prolonged pollination period.
It also produces exine precursors, orbicules
, and sporophytic recognition proteins and lipids which form the pollen coat (or pollenkitt or tryphine) (Echlin, 1971; Pacini et al., 1985).
The function and contents of these orbicules
, which are typically 1 to 2 mm in diameter, are unknown.
It has been reported that  orbicules
originate in the cytoplasm of the tapetal cells as lipoidal pro-orbicular bodies that accumulate below the membrane and eventually extrude to the cell surface (facing the locule) where they provide sporopollenin precursors for exine formation.