The "Gymnosperms" comprise cycads, Ginkgo, conifers and Gnetales. The gym-nosperm pollen wall differs from that in angiosperms in two characters: 1. the endexine is always lamellate in mature pollen stages. 2. the infratectum is never columellate. The four gymnosperm classes exhibit diverse, special constructions of the apertures.
The principal stratification (ektexine, endexine and intine) of the gymnosperm pollen wall is identical to that of angiosperms. A tectum is present in all cycads, in Ginkgo, in all Gnetales, but not in all conifers: in some taxa the tectum is completely lacking (sculpture elements are situated on the foot layer). The infratectum is either alveolate or granular but never columellate.
A special terminology is applied to saccate pollen, i.e., Pinaceae and Podocarpaceae. The saccus is a large hollow projection from the corpus, the central body of saccate pollen grains. It is a typical deviation of the pollen wall conformation, composed only by the exine with an alveolate infrastructure. Most frequently, two sacci are present, in some taxa even three, or only a single one. Saccate pollen grains show on the proximal side of the corpus a region termed cappa, and on the distal side a thinned region, the leptoma.
In Pinus two pollen types are recognized as of systematic value. The Haploxylon-pollen-type is characterized by pollen grains with broadly attached half-spherical air sacs - in LM the leptoma shows remarkable thickenings (black spots). The Diploxylon-pollen-type is characterized by pollen grains with narrowly attached, spherical air sacs - the leptoma does not show any thickenings.
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