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Characteristics of Wood Structure in Gymnosperms and Their systematic Significance

Zhou Yin, Jiang Xiao-Mei   

  • Received:1900-01-01 Revised:1900-01-01 Online:1992-09-10 Published:1992-09-10
  • Contact: Zhou Yin

Abstract:

The systematic positions and taxonomic ranks of orders and families
in Gymnosperms, especially those in Coniferopsida, are analysed and discussed in
this paper based on the evolutionary trends in the wood structure. The opinions
of the present authors are as follow:
    1. The separation of the Araucariaceae from the Coniferae and establishment
of the Araucariales are reasonable,because the intertracheid pitting in the wood is
the Araucarioid type and there are no pits on both horizontal and end walls of
ray parenchyma cells in the family.
    2. The position of the genus Ginkgo in Cheng’s system is acceptable. Ginkgo
is more similar to Coniferae than to Cycadaceae in the wood structure.
    3. According to the characteristics of wood structure, arrangement of the
Podocarpaceae, Cephalotaxaceae and Taxaceae between the Araucariaceae and the
Pinaceae is reasonable. Among these families, the Cephalotaxaceae and Taxaceae
are more closely related to each other in the view of the spiral thickenings which
often appear on the inner wall of wood tracheids.
    4. Further evidence for the establishment of the Sciadopitysaceae is provided.
For example, most of cross-field pits in the wood of the Sciadopitysaceae are win-
dow like, while some of them are of the Lemon type or the Subtaxodioid type;
bordered pits are of the Araucaria B type.
     5. The characteristics of wood structure in the genus Platycladus differ greatly
from Thuja. The former has cross field pits of the Cupressoid type, bordered pits
of Araucaria B type and warty layer on the inner surface of tracheids. All of
these characteristics have added further evidence for the separation of Platycladus
from Thuja.
    6. Based on the structural characteristics of woody rays in the Pinaceae, the
most primitive genera are Abies, Keteleeria and Pseudolarix, while more advanced
ones are Cedrus and Tsuga, and even more advanced ones are Pseudotsuga,
Cathaya, Picea and Larix, all of which share normal resin canals. The most ad-
vanced genus is Pinus which is also of normal resin canals. Pinus can be divided
into three subgenera, Haploxylon, Parry and Diploxylon, according to the presence
or absence of dentation and warty layer in wood tracheids.
    7. It is reasonable to place the genus Amentotaxus in the Taxaceae, because
membrane of bordered pits in the genus is similar to that in the other four genera
of the Taxaceae, both of the Araucaria type.
    8. The present authors agree with Cheng’s (1978) treatment of Sect. Heopeuce
in Tsuga, based on the fact that Tsuga longibracteata has traumatic resin canals
and warty layer.
    Reducing Pinus hwangshanensis into P. taiwanensis, made by Cheng, is reason-
able because of the similarities between P. hwangshanensis and P. taiwanensis in
the wood structure.
    The establishment of a new subgenus, Patty, for Pinus bungeana is suitable
based on chemotaxonomy, morphology and the distinct warty layer on the inner
surface of wood tracheids.

Key words: Wood structure, Phytotaxonomy, Phylogeny, Gymnosperms, Coniferopsida, Araucariales, Sciadopitysaceae.

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