A highly interesting observation concerns Sauromatum venosum (Araceae), which has inaperturate pollen grains with an endexine and spines, both polysaccharidic in nature (Weber et al.
data) reflecting the process of endexine development in the same species (El-Ghazaly et al.
Pollen wall and tapetum development in Anaxagorea brevipes (Annonaceae): sporoderm substructure, cytoskeleton, sporopollenin precursor particles, and the endexine problem.
Three different electron- dense layers form the pollen grain wall: ectexine with interrupted tectum, columellae and foot layer; endexine and intine still in formation.
The exine has a very thin endexine layer, and a fibrilar intine with numerous invaginations coated by the plasmalemma can be observed.
The endexine is the inner part of the exine, is located above the foot layer and has a different electron density than the foot layer.
Using transmission electron microscopy (TEM), Nowicke and Skvarla (1983: 181) noted that "[t]he endexine
appears loose and fragmented near the apertures" in extant Itea pollen; if the same is true of the fossil grains, this may explain the textured appearance of the exine surrounding the pores under light microscopy.
A number of characters vary at too low a level to be useful (are highly homoplastic at tribal level), for instance pollen grain size and shape, number of infractectum layers and their thicknesses, extent and depth of cavea, spine shape and internal structure, number and size of abporal, interporal, paraporal and poral lacunae, and internal endexine
: (0) thick, under apertures only; (1) endexine
throughout, thickened under apertures; (2) endexine
throughout, not thickened under apertures; (3) endexine
absent under apertures.
endoaperture in the endexine and/or membranous granular layer MGL (see
layer differs from the endexine in having fewer lipids and more proteins
The systematic value of endexine
ornamentation in some Psychotrieae pollen (Rubiaceae-Rubioideae).