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On the systematic position of Taxaceae from the embryological and anatomical studies

Wang Fu-Hsiung, Chen Zu-Keng, Hu Yu-Shi   

  1.  (Institute of Botany, Academia Sinica)
  • Received:1900-01-01 Revised:1900-01-01 Online:1979-08-18 Published:1979-08-18
  • Contact: Wang Fu-Hsiung

Abstract:

 Florin has suggested that the Taxaceae should be separated from the Coniferales
to erect an order of its own. His basic argument is that the ovule of the taxads is
terminal while the ovules of the conifers are lateral. Florin's idea was accepted by
many taxonomists and some of them make an even higher taxon as Taxopsida.  The
present paper deals with the systematic position of Taxaceae from the embryological
and anatomical studies in comparison with those of other members of the Coniferales.
     The extant Taxaceae includes five genera, namely, Taxus, Pseudotaxus, Austro-
taxus, Amentotaxus and Torreya.
     The mature pollen grains of Taxaceae contain two ceils (Torreya) or one cell only
(Taxus, Pseudotaxus and Austrotaxus).  No prothailial cells are formed.  Two sperms
are of unequal size.  The number of free nuclei formed in the female gametophyte is
256(-512).  The arehegonia vary from I to 25, with 2 to 8 as the usual range.  The
proembryo of Torreya forms 4 or 8 free nuclei, while all other genera of the Taxaceae
usually contain 16(-32).  Cleavage polyembryony is present in Torreya, but absent
in other genera.  The proembryogeny belongs to the standard type of the Coniferales.
     The bark of the Taxaceae possesses erystalliferous fibers. No crystals are formed
in parenehyma Rays are homogeneous and consist of ray parenchyma cells only.
     Growth rings of the wood in Taxaceae are distinct. Axial tracheids with bordered
pits usually uniseriate, occasionally paired or biseriate, with spiral thickenings.  Wood
parenchyma is present in Amentotaxus and Austrotaxus, but absent in Pseudotaxus,
Taxus and Torreya.  Cross-field pits cupressoid.  Resin canals and ray tracheids are
absent.
     Considering Taxaceae as a natural taxon each of the main embryological and
anatomical characters is to be seen in other families of the Coniferales though the
combination is unique, making it a distinct family.  Many differences between Taxa-
ceae and other families of the Coniferales fall within the range of the variation in the
conifers.  However, Pinaceae is a rather specialized  family  among the  Coniferales.
Thus, the difference between Taxaceae and Pinaceae is quite striking.
      Florin agreed with Wilde (1944) that some species of Podoca rpus with single
ovule are derived from that with multiple ovulate cone and represent the last stage
of reduction of the cone.  On the other hand, the taxads with their terminally borne
ovule are considered as primitive.  It is obvious that Florin's explanation is hardly
convincing.  Many authors such as Chamberlain (1935), Takhtajan (1953) and others
pointed out that single ovulate cone of the Taxaceae was very probably derived from
the one with multiple ovulate cone.  Recently  Keng  (1969)  considered  that  the
Taxaceae is closely related to Cephalotaxaceae on one hand and connected with the
Podocarpaeeae by way of Phyllocladus on the other hand.  It is concluded that Florin's
suggestion is not supported by our investigations based upon the embryological and
anatomical features ef the Taxaceae by comparing them to those of other families of
the Coniferales.  The systematic position of the Taxaceae should be placed under the
Coniferales.