Chen Tsu-Keng, Wang Fu-Hsiung
J Syst Evol. 1978, 16(2): 1-10.
The embryogeny of Pseudotaxus chienii Cheng, a member of Taxaceae, has been
investigated. Pseudotaxus is endemic to China and its distribution is restricted to
Lung-chuan County, Chekiang, Ching-kang Mountains, Kiangsi and Sze-ming Mountains, Kwangsi. The material used for the embryological study was collected in 1964
from Lung-chuan, the type locality of Pseudotaxus.
Fertilization took place within the last week of May, 1964. The fertilized egg
undergoes four mitotic divisions in succession without wall formation and a proembryo of 16 free nuclei is formed. Then the wall formation follows. The 16 cells of
the proembryo are arranged in two groups, the upper one being the open tier (O)
and the lower, the primary embryo cells (PE). The relative number of cells (O :PE)
is usually 9:7, occasionally 10:6 or 8:8, rarely 7:9. The cells in the open tier are
often not walled above. The division of the open tier results in the formation of the
upper tier and the prosuspensor. While the prosuspensor cells begin to elongate the
divisions of the primary embryo cells give rise to the embryo cells (12-18 cells).
Usually two archegonia in the same ovule are fertilized and two embryonal systems are developed. Thus, simple polyembryony prevails. In addition, several supernumerary embryonic masses may be found above the prosuspensor cells but they
are usually ephemeral because of lack of sufficient nutrients in later stage. Cleavage
polyembryony is absent in Pseudotaxus.
A cap cell is usually formed at the apex of the young embryo. In later stages
of embryonal development root initials contribute mainly to the procambium and
embryonic cortex but less to the root cap. The embryo matured about the middle
of September, 1964. The mature embryo has two cotyledons. No pith is formed in
the central cylinder. No secretory elements are developed in any part of the embryo.
The suspensor is well developed and becomes massive while the root cap is rather
weak. The similarities in the embryogeny between Pseudotaxus and Taxus are very
striking. They have a similarity in the development and general structure of the
proembryo; cleavage polyembryony is absent while simple polyembryony prevails;
both have no pith and no secretory elements in the mature embryo.
Based upon the results obtained from the present investigation in Pseudotaxus
the authors consider that the systematic position of Pseudotaxus in Taxaceae may be
arranged as follows: Taxus, Pseudotaxus, Austrotaxus, Amentotaxus and Torreya.
Among them Taxus and Pseudotaxus are relatively primitive and Torreya is the most
advanced, while Austrotaxus and Amentotaxus are between. The embryological data
do not support the viewpoint of Florin that Taxaceae should be removed from Coniferales and a parallel order Taxales should be established.
