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

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

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

(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

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.

Wang Fu-Hsiung, Chen Zu-Keng, Hu Yu-Shi. On the systematic position of Taxaceae from the embryological and anatomical studies[J]. .

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

Knowledge

Abstract

Cite this article

share this article

References

Related Articles 0

Recommended Articles

Metrics

Comments