作 者 ：Fu De-Zhi
期 刊 ：植物分类学报 1992年 6期
Keywords:Nageiaceae D. Z. Fu, Female reproductive organs, Female strobilus,
Abstract:
A new monotypic gymnosperm family, Nageiaceae D. Z. Fu, is sepa-
rated from Podocarpaceae. It is characterized by having multinerved leaves with-
out costae, and primitive shoot-like female reproductive organs (female strobili).
The new family contains a single genus consisting of 2 sections, 5 species and is
distributed along the western coast of the Pacific, from low coastal mountains of
eastern and southern Asia to the Phillipines and Papua New Guinea.
The first species in the Nageiaceae was described as an angiosperm, Myrica
nagi Thunb. (1784), but it was soon recognized to be a gymnosperm belonging
to a new genus, and was renamed as Nageia japonica Gaert. (1788). The generic
name, Nageia, however, has seldom been used, and the members of Nageia have
generally been treated as an isolated section of Podocarpus in the Podocarpaceae.
When revising the Podocarpaceae, De Laubenfels (1969) established a new genus
Decussocarpus based on Nageia, but several years later (1987) he revived the old
generic name, Nageia. Page ( 1988,1990)considered Nageia to be a valid generic
name and redefined it as a natural genus.
The distinctive,broadly lanceolate, multinerved leaves (without costae) of Nageia
are rather unusual in gymnosperms,only being similar to those of Agathis in the
Araucariaceae, their leaves are also similar to each other in anatomy. For example,
there are many single vascular bundles arranged parallelly, between which
occur sclerenchyma cells in the mesophyll. Apparently,leaves in Nageia are rather
similar both externally and internally to paleogymnosperm cordaitean leaves, and
sclerenchyma cells found in Nageia might be the remains of straps between veins
in cordaitean leaves. In addition to leaf characters, the large and nearly round
pith of the young shoot in Nageia appears to be a reminiscent of the large pith in
cordaitean stem.
The female reproductive organs (female strobili ) in Nageia are shoot-like.
The female strobilus has a sterile terminal bud, and several opposite or
subopposite sterile scaly bracts on its axis; two opposite megasporophylls are
found near the axis apex and both have an anatropous ovule which is almost en-
tirely covered by the megasporophyll; a bract is partly adnate to the lower back
of the megasporophyll;mature arillate seeds are 1-2 or occasionally 3 in number;
the axis becomes woody when the seeds mature, but in some species (N.
wallichiana) the upper part of the axis becomes fleshy (in the shape of a receptacle),
in which no distinct boundary was found between the fleshy receptacle and the
woody part, and both have the same scaly bracts or traces.
Many characters in Nageia are distinctly different from those in Podocarpus.
Leaves in the Podocarpaceae have distinct midribs; in Podocarpus, the reproduc-
tive organ, which was generally thought to be similar to that in Nageia, has no ter-
minal bud, and its bract is entirely free from the lower back of the
megasporophyll, the fleshy receptacle is derived from both the axis and the sterile
bracts (except the lowest two), and the female strobilus at the seed stage has a sec-
ondary stalk.
The multinerved leaf in Nageia can rarely be found in most of the living
gymnosperms except in some rather isolated groups, such as Araucariaceae,
Ephedraceae,Ginkgoaceae and Welwitschiaceae. Paleobotanical evidence shows that
multinerved leaves have been found in all of the geological ages from the Paleozoic
to the present, and such a shoot-like female reproductive organ as in Nageia was
found in some paleogymnosperms. It is very difficult to determine the systematic
positions of these fossil plants because of lacks adequate material of reproductive
organs or even lack of complete vegetative organs. The vascular system and
leaf characters of gymnosperms are considered to be very conservative, and the
fact that the common leaf shape and venation exist in both fossil and living
gymnosperms could imply that there exists a multinerved-leaved evolutionary
line ( M-line ) in gymnosperms, which could be traced back to the
paleogymnosperm cordaitean plants or even older ones with multinerved leaves.
The different types of the female strobili (female reproductive organs) of living
gymnosperms, regardless of having one or only several seeds without a typical
cone or many seeds with a cone, might have been derived from shoot-like or spike-
like female reproductive organs possessed by their common ancestor.The fossil eviden
ce shows that the typical cone similar to those of living gymnosperms first appeared
in the Jurassic, much later than the single-seeded fossil plant without cones. The seed
fossil appeared in the late Devonian Period. It is very difficult to infer the relationships
among living gymnosperms, which are hardly derived from one another. But an
analysis of the strobili, including the axis structure and position, number,
morphology and degree of adnation of the phyllomes on them, would be helpful
to the study of their phylogeny. It is evident, therefore, that the gymnosperms
with leaves having a midrib might also have a rather long evolutionary course,but no
transition between the midrib and multinerved patterns of leaf venation has so far
been found in both living and fossil plants.
Finally, it is noteworthy that the Nageiaceae are distributed along the western
coast of the Pacific, where many primitive representatives, both in gymnosperms
and angiosperms, still survive. This would be advantageous to the consideration
of Nageiaceae as a primitive representative, or a descendant of fhe paleogymnos
-perm cordaitean plants.