.Studies on Pollen Morphology and Exine Ultrastructure in Cephalotaxaceae[J].Journal of the Graduate School of the Chinese Academy of Sciences,1993,31(5):425-431.
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| Authors: | Xi Yi-zhen |
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| Abstract: | The pollen morphology of Cephalotaxaceae was examined with LM,
SEM and TEM. Pollen grains in this family are spheroidal or subspheroidal,
rounded in polar view, but usually wrinkled with irregular shape. Pollen size is
22.6- 34.8 μm in diameter. There is a distinct or indistinct tenuity on distal face.
The tenuity occasionally slightly rises above the outline of pollen grains, but often
sukened. Exine rather thin, 1—1.5μm thick, layers obscure, surface of pollen
grains is nearly psilate or weakly granulate. Under SEM exine is covered with
fine and dense granules, and sparse Ubisch bodies are found on the granular lay-
er. The Ubisch bodies are provided with minute gemmate processes on the surface.
Acorrding to our observation under TEM, exine consists of ectexine and lamellate
endexine, with the former divided into outer ectexine of granules densely arranged
and inner ectexine of loosely arranged microgranules. Granules of the outer
ectexine are relatively thick, and connected with each other, forming a structure
just like tectum or separate from each other. Microgranules of the inner ectexine
are distinct or indistinct. Endexine is provided with 5- 7 lamellae.
As far as information of pollen morphology is concerned, Cephalotaxus oliveri
is rather special in the Cephalotaxaceae. First, the tenuity in pollen grains occu-
pies one half of the distal part, much larger than that of the other species in the
family. Second, the ectexine in Cephalotaxus oliveri may be divided into two dis-
tinct layers, outer ectexine and inner ectexine. The former is made of a layer of
sporopollenin masses, which are connected with each other to form tectumlike
structure, while the latter consists of a layer of loosely arranged granules or small
segments of sporopollenin. The inner ectexine is different from that of other species
by having a thicker layer of sporopollenin granules. Based on these two features,
we support the division of Cephalotaxus into two Sections, Sect. Pectinatae and
Sect. Cephalotaxus.
Pollen grains of Cephalotaxaceae are similar to those of the Taxaceae in
having spheroidal shape and the tenuity on its distal face. These characteristics
strengthen the evidence for a close relationship between the Cephalotaxaceae and
Taxaceae. Although pollen grains of the Cephalotaxaceae and Taxaceae are similar
in some characteristics, they have obvious differences in , for example, size of
tenuity, the fine structure of Ulbisch bodies and of the outer and inner ectexine.
On the basis of pollen morphology, the present author considers theCephalotaxaceae slightly more primitive than the Taxaceae. |
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| Keywords: | Cephalotaxaceae Ultrastructure Pollen morphology Cephalotaxus oliveri |
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