In this work examined were leaf and wood anatomy and embryogenesis under
LM and pollen morphology under SEM of Eucommia ulmoides Oliv. The results were used for
a comparison between the family and Ulmaceae and Hamamelidaceae respectively. The taxon-
omic rank and relationships of E. ulmoides were analyzed mainly based on the spiral thicken-
ings on lateral walls of vessels in the secondary xylem, the presence of iridoid, embryology and
palynology.
1. The present authors tend to support Keng's (1962) view that the spiral thickenings on la-
teral walls of vessels are the remnant of a primitive character. The spiral thickenings on lateral
walls of vessels in E. ulmoides (Plate 1: 9) are similar to those of some genera of the Hamameli-
daceae (e. g. Altingia Noronha), while vessels in Ulmaceae lack spiral thickenings on lateral
walls. The Eucommiaceae with simple perforations plates (Plate 1: 9) is more specialized than
the Hamamelidaceae.
2. Based on the fact that the Eucommiaceae contains iridoid compound and has unitegmic
ovules and cellular endosperm, Dahlgren (1980, 1983) places with uncertainty the family in Cor-
niflorae as an order, a treatment which is widely discrepant from those of Takhtajan (1980),
cronquist (1981) and thorne (1983). Though containing iridoid compound, the Eucommiaceae
is different from Corniflorae in a combination of characters in external morphology, woody
anatomy and embryology. The compound has also been found in Liquidambar L. (Hamameli-
daceae) but not in the Ulmaceae, which is another piece of evidence showing a close relation-
ship between Eucommiaceae and Hamamelidaceae.
3. The development of microsporangia and megasporangia, as observed in the present
work, is basically in accordance with that reported by Tang (1962) and Eckardt (1963), but
the haustoria present both at the micropylar end and at the chalazal end and 4-celled proembryo
of the Solanad Type are reported here for the first time.
It can be seen from Table 2 that the Eucommiaceae and the Hamamelidaceae have a nu-
mber of embryological characters in common For example, glandular tapetal cells in an-
thers are usually multinuclear; cytokinesis of meiosis of pollen mother cells is simultaneous;
microspores develop into tetrahedral; ovules are anatropous, crassinucellate; embryo sacs are
of the monosporic Polygonum Type; endosperm is cellular (Plate 3: 5-7; 4: 1-3; 5: 1-3;
Fig. 1: 1-3,5). The Eucommiaceae is also embryologically related to the family Ulmaceae,
but the family under study is more specialized than the two families mentioned above in uni-
tegminy (Plate 4: 3,4), proembryo of the Solanad Type (Plate 6: 3; Fig. 2: 4), coexistence
of micropylar haustoium (Plate 6: 4-6) and chalazal hustorium, especially in the Eucom-
miaceae the epidermis and the endothecium are widely separate (Plate 3:3), a feature which
has never been seen in angiosperms to our knowledge.
4. Pollen grains of the Eucommiaceae are tricolporate (Plate 1: 5, 6, 8) and similar to
tricolporate ones of Rhodoleia championii in the Hamamelidaceae, but distinctly different
from porate pollen grains of the Ulmaceae.
5. Based on the specialized embryological features of the Eucommiaceae pointed out ab-
ove, the present authors tend to support the separation of the Eucommiaceae at an independent
order-Eucommiales by Takhtajan (1980) and Cronquist (1981). Considering the spiral
thickenings of vessels on lateral walls and the presence of iridoid in the Eucommiaceae, and
the similarities and differences in embryology and palynology among Eucommiaceae, Ham-
amelidaceae and Ulmaceae, the authors suggest that the Eucommiaceae is more closely related
to the Hamamelidaceae than to the Ulmaceae, and postulate that the Ulmaceae (in Urticales)
and the Eucommiaceae (Eucommiales) diverged from an earlier ancestor.
