| 银杏雌性生殖器官的形态学本质及其系统学意义 |
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| 引用本文： | 傅德志,杨亲二.银杏雌性生殖器官的形态学本质及其系统学意义[J].中国科学院研究生院学报,1993,31(3):294-296. |
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| 作者姓名： | 傅德志 杨亲二 |
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| 摘 要： | 关于古老裸子植物银杏Ginkgo biloba L.雌性生殖器官形态学本质的问题争论
很多,因此这一类群的分类位置尚存争议。本文进一步发展了Florin提出的“种鳞复合
体(Seed-scale complex)”概念,提出解释裸子植物生殖器官形态演化的“苞鳞一种鳞复
合体(Bract-scale and seed-scale complex)概念和演化理论,并试图用以解释银杏的生
殖器官形态学本质和裸子植物系统发育的有关问题。由银杏着生胚珠的结构(Ovuliferous
structure)生于可育短枝上鳞状叶叶腋的事实,赞同该结构为次级轴性(枝性)性质,提
出该次级轴性结构及连同下部的鳞状叶相当于裸子植物大部分类群所具有的苞鳞—种
鳞复合体(Bract-scale and seed-scale complex),并保留了较多的原始古老性质,可能
代表着苞鳞—种鳞复合体较原始的形态式样。该结构的鳞状叶与可育短枝上正常的营
养叶均为不育苞片的性质,鳞状叶叶腋生出的长柄则是次级轴性结构的次生性伸长,长
柄上部二分叉的着生胚珠结构相当于该次级轴性器官仅存的极度退化的二枚可育叶性器
官,而整个可育短枝相当于一个分化程度很低的复合大孢子叶球。银杏生殖器官中的某
些性状与苏铁十分相似,但由于苞鳞一种鳞复合体的出现,标志着这一类群已远较苏铁特
化,并应与所有具苞鳞—种鳞复合体的类群在同一条演化线上,即苞鳞—种鳞复合体
演化线(Bract-scale and seed-scale complex evolutionary line,BS-line),而不具苞鳞
—种鳞复合体的苏铁类(Cycas)则构成裸子植物中的苏铁演化线(Cycas evolutionary
line,C-line)。银杏大孢子叶球的式样,可能代表着裸子植物一种早期的原始大苞子叶
球式样,为古裸子植物不甚分化的可育枝条向高度压缩和变态的可育枝条(苞鳞一种鳞复合体及典型的球果)演化的一种中间过渡式样。
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| 关 键 词： | 银杏 雌性生殖器官 苞鳞—种鳞复合体 裸子植物系统学 |
A New Morphological Interpretation of the Female Reproductive Organs in Ginkgo biloba L., with a Phylogenetic Consideration on Gymnosperms |
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| Fu De-zhi,Yang Qin-er.A New Morphological Interpretation of the Female Reproductive Organs in Ginkgo biloba L., with a Phylogenetic Consideration on Gymnosperms[J].Journal of the Graduate School of the Chinese Academy of Sciences,1993,31(3):294-296. |
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| Authors: | Fu De-zhi Yang Qin-er |
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| Abstract: | The ovuliferous structure of Ginkgo biloba L. has been variously inter-
preted morphologically. As a result the systematic position and the relationship
with other gymnosperms of this ancestral gymnosperm have long been under dis-
pute. In the present paper, a brief survey of the main views as to the nature of
the ovuliferous structure is givcn. Based on morphological and teratological data
previously reported, a new interpretation is proposed. The essential points are
summarized as follows:
1. In morphological essence, a fertile dwarf shoot with some ovuliferous struc-
tures in Ginkgo biloba L. might as a whole be nothing but a megasporophyll
strobilus (female cone), which is shared actually by all the conifers in the
gymnosperms. The fertile dwarf shoot has appearance extremely similar to that of
the vegetative dwarf shoot, suggesting that in Ginkgo biloba L. the vegetative or-
gans and the reproductive organs have not been yet well differentiated, and thus
its megasporophyll strobilus might represent one of the most primitive compound
strobilus types.
2. In Ginkgo biloba, the ovuliferous structure borne in the axil of a scale
leaf (sometimes a normal leaf) on the dwarf shoot, together with the scale leaf it-
self, might be the homogenous organ corresponding to the bract-scale and
seed-scale complex of the compound female strobilus of the typical conifers. The
complex is a relatively isolated reproductive unit on the strobilus. The normal
leaves and the scale leaves on the dwarf shoot might be equivalent to the
bract-scales in the typical cones, though the normal leaves still retain the vegetative
nature as the foliage leaves on the vegetative shoot. The stalk hearing ovules at its
top might be equivalent to a seed-scale of the typical cones.
3. The megasporophyll strobilus in Ginkgo biloba, namely a whole fertile dwarf
shoot as mentioned above, seems to show much more primitive characteristics
than those of typical conifers. In this plant it is very difficult to distinguish the fer-
tile dwarf shoot from the common vegetative dwarf shoot before reproduction
time. Moreover, its megasporophyll strobilus often exhibits more atavistic abnor-
malities than those of other conifers. All the evidence indicates that the primitive
ancestor of conifers might have had the fertile organs which might be of basically
identical morphology as vegetative shoots, except that in the fertile organs there
might exist numerous fertile leaves bearing one or many ovules.
4. The longer stalk of the ovuliferous structure in Ginkgo biloba might have
come from mainly a secondary elongation growth of the seed scale, and only a lit-
tle part of it might be the remains of the original shoot. The fork structure bear-
ing ovules at the top of the stalk might be the rudementary part of the petioles of
the only two extremely reduced megasporophylls. The collar around the base of
the ovule might be a secondary protective structure.
5. A correct morphological interpretation of the female strobilus in Ginkgo biloba
is doubtless of important significance for our better understanding of the evolution
of the female reproductive organs in conifers. According to our interpretation men-
tioned above, together with the concept of the bractscale and seed-scale complex
proposed in the present paper, which is mainly based on the concept of the
seed-scale complex propose by Florin, here we put forward an evolutionary theory
of the bract-scale and seed-scale complex. According to this theory, the female reprodu-
ctive organs of the ancestral conifers should be very similar, as mentioned above, to
the sterile foliage shoot except that the former might have some fertile leaves which
could produce ovules at reproduction time. This ancestral female reproductive or-
gan type might have had evolved towards two directions and thus formed two
main evolutionary lines. One is represented by the genus Cycas and we may call
it the Cycas Evolutionary Line (C-line), in which the megasporophyll strobilus is
monopodial, with the fertile leaves and sterile bracts occurring directly on the
main axis. The Cycadaceae is the only living gymnosperm member along this evo-
lutionary line. The second line is represented by all the conifers including Ginkgo,
which all have the structure of the bract-scale and seed-scale complex, and thus we
called it the "Bract-scale and Seed-scale Complex Evolutionary Line" (BS-line).
The members along this line have multipodial female strobilus, i.e. compound
strobilus. On the main axis occur some sterile vegetative bracts. In the axils of
some or most of the bracts occur the seed-scales. The seed-scales are actually the re-
mains of the extremely, or smetimes completely reduced fertile shoots. Each part
of the bractt-scale and seed-scale complex and the main axis of the strobilus could
have undergone independent or correlated changes, and thus have had formed vari-
ous types of strobilus which are found in the living conifers.
6. Our theory on the evolution of the bract-scale and seed-scale complex seems
to support the division of all the gymnosperms into two major groups as pro-
posed by Chamberlain, and is also in favour of the placement of Ginkgo biloba
into the conifers as the most primitive member along BS-line.
7. Based on their similar morphological characters, it can be considered that
Ginkgo biloba might have close relationships with the Nageiaceae, Ephedraceae,
Welwitschiaceae and Araucariaceae. All these groups have multinerved leaves with-
out costa. These living gymnosperms might have a more direct relationship withthe ancestral cordaites. |
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| Keywords: | Ginkgo biloba L Female reproductive organ Bract-scale and seed-scale complex Systematics of gymnosperms |
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