走出歌德的阴影:迈向更加科学的植物系统学

传统的植物学理论中,被子植物雌蕊的基本单位心皮被认为是变态的叶(即大孢子叶)通过纵向对折和内卷演化而来。该理论造成了被子植物和裸子植物之间不可逾越的鸿沟。近年来提出的一统理论认为被子植物的心皮由长胚珠的枝和包裹这个枝的叶共同组成,从而弥合了被子植物与裸子植物之间的鸿沟。最近,当代植物学界两大权威人物Peter R. Crane和PeterK.Endress分别撰文,发表了不同于传统理论的观点。Endress认为,心皮由胚珠和叶性器官组成;而Crane认为,所有的胚珠都长在枝上。结合二者的结论,不难得出"心皮实际上等同于一个长胚珠的枝加上一个叶"的论断。这在某种意义上等于认同了一统理论的观点。两位权威人物观点的转变预示着植物学理论将很快发生根本性的转变。该文向国内植物学同行通报这一最新动态,以期让我国学者能够了解最新理论。     

松杉类裸子植物的大孢子叶球理论评述

系统评述了迄今为止在裸子植物球果类种鳞形态学本质方面存在过的各种观点及研究进展。将 这些观点归纳为7大类：(1)Delpino和Penzig等主张种鳞为叶性器官的叶性说;(2)Sachs和Eichler认为种鳞相当于叶舌的叶舌说;(3)Bessey认为种鳞不过是胚珠合点端增生的结果的独特结构说;(4)Kubart等提出生胚珠构造的假种皮学说;(5)Arber的半枝学说;(6)Dupler的珠被说认为红豆杉类胚珠的肉质化部分为珠被性质的构造;(7)由Schleiden和Braun提出并由Florin等发展的枝性说则以充分的证据论证了种鳞的枝性本质。关于球果类裸子植物种鳞的性质和来源,本文作者赞同Florin枝性本质的论述;但对该构造现存式样的组成和演化过程,笔者认为该构造是在个体发育中不甚分化的专营生殖的枝性复合构造,由早期裸子植物次级生殖枝及其相关构造经过系统发育变态、融合演化形成。     

关于豆科植物心皮缝合线朝向的思考

当今植被和地球生态系统中多样性最高的类群是被子植物。豆科植物是被子植物中的第三大科,因其重要的经济价值与人类的生活密切相关,颇受植物学家的重视。百余年前植物学家已基本明确回答了豆科植物的许多形态学问题,但仍然有一个问题不甚明确。单枚心皮是豆科植物的一个重要特征。植物学家认为该心皮缝合线朝向心皮的腹面。这种解读某种程度上是人们对木兰类心皮理解的合理延伸,也是形态演化理论所期望的。但事实上,豆科植物除了单心皮外还有多心皮的属种,其胚珠着生位置及心皮缝合线朝向各异。它们之间的演化关系如何?这个问题的答案与我们对被子植物的形态和演化历程的理解关系甚大,这里提出来与大家一起思考和研究。     

紫玉盘

正紫玉盘(Uvaria macrophylla Roxb.)为番荔枝科(Annonaceae)紫玉盘属植物,直立或攀缘灌木。幼枝、幼叶、花序轴或果序轴均被星状柔毛。叶革质,长倒卵形或长椭圆形,长10～23 cm,宽5～11 cm,顶端急尖或钝,基部近心形或圆形。花1～2朵与叶对生,红色,直径2.5～3.5 cm;花瓣6片,2轮,内外轮花瓣相似,卵形,长约2 cm,宽约1.3 cm;雄蕊线形,长约9 mm,药隔卵形,无毛,最外面的雄蕊常退化;心皮长圆形,长约5 mm,每枚心皮有胚珠6～8颗,2列。成熟心皮卵状,长     

山玉兰中3～7个胚珠的发现

通过对山玉兰（Ｍａｇｎｏｌｉａｄｅｌａｖａｙｉ）两个居群各１０个果的解剖,发现其心皮中的胚珠数目是变化的,１个果上的心皮中分别具有２～７枚胚珠,１心皮具有３、４、５、６和７枚胚珠的数目在木兰属中首次发现。在木兰科中,心皮中所具有的胚珠数目是分属的重要依据之一,木兰属和木莲属是根据心皮中胚珠的数目来划分的,前者具２胚珠,而后者具４～１６胚珠。木兰属中具３、４、５、６和７胚珠心皮的发现有力地支持了Ｂａｉｌｏｎ所提出的将木莲属与木兰属归并的分类观点     

扫描电子显微镜下的子房外生胚珠

众所周知,被子植物的胚珠都包被于子房之内,这也是被子植物区别于裸子植物最重要的特征,但在某些杂种后代中却出现了异常现象。图中的子房外生胚珠是在北京卧佛寺的一株小叶杨和青杨的杂交植株上发现的。杨树通常是雌雄异株,柔荑花序,花序轴每节     

凹叶厚朴大、小孢子发生和雌、雄配子体发育的研究

凹叶厚朴花药四囊型,腺质绒毡层有1-2层细胞,小孢子形成时胞质分裂方式为修饰性同时型,小孢子四分体排列方式为左右对称型．成熟花粉粒为二细胞型。四分体和小孢子在发生时有不规则变形。子房单心皮,心皮腹面壁上着生2个胚珠,胚珠倒生型,厚珠心,双珠被;孢原细胞一个,并且自表皮下第2层细胞处分化。胚囊发育为单孢蓼型。凹叶厚朴的胚胎学特征与木兰科其它植物的胚胎学特征基本相同,属于较原始的被子植物胚胎类型。在凹叶厚朴大、小孢子发生和雌、雄配子体发育过程中存在部分败育现象。本文初步探讨了凹叶厚朴濒危的生殖生物学原因。     

漫谈植物的心皮

在显花植物中,花内着生胚珠的器官叫做心皮.心皮又称为大孢子叶,它是构成雌蕊群的基本单位,是一原始的伸长的变态叶.心皮在茎上的着生位置、排列,维管束的联系、解剖和个体发育均同叶与茎的关系一样.组成雌蕊群的心皮数目,因植物种类不同而异,有的雌蕊群由一个心皮组成,如大豆等;有的由二个或二个以上的心皮组成,如油菜、柑橘等.如果一朵花中有两个或两个以上的心皮,它们可以是彼此分离的,形成离生心皮雌蕊,如毛茛、八角茴香等;也可以是相互连合的,形成合生心皮雌蕊,如梨、苹果等.     

凹叶厚朴大、小孢子发生和雌、雄配子体发育的研究

凹叶厚朴花药四囊型,腺质绒毡层有1-2层细胞,小孢子形成时胞质分裂方式为修饰性同时型．小孢子四分体排列方式为左右对称型,成熟花粉粒为二细胞型。四分体和小孢子在发生时有不规则变形。子房单心皮。心皮腹面壁上着生2个胚珠,胚珠倒生型,厚珠心,双珠被;抱原细胞一个,并且自表皮下第2层细胞处分化。胚囊发育为单孢蓼型。凹叶厚朴的胚胎学特征与木兰科其它植物的胚胎学特征基本相同,属于较原始的被子植物胚胎类型。在凹叶厚朴大、小孢子发生和雌、雄配子体发育过程中存在部分败育现象。本文初步探讨了凹叶厚朴濒危的生殖生物学原因。     

观察“心皮是变态叶”的好材料——日本晚樱

在讲授花的概念和结构时,我们说花是适应于生殖的变态短枝．花的各个组成部分是叶的变态。花萼、花冠是叶的变态,学生较易理解接受,而雄蕊和雌蕊是叶的变态,学生难以理解。而“心皮”是我们学习植物学必须掌握的一个名词。它是构成雌蕊的基本单位,是具有生殖作用的变态叶。究竟为什么说“心皮是变态叶”．很多学生更是无法理解。笔者通过认真地观察,发现了一种观察“心皮是变态叶”的好材料——日本晚樱。     

Glossopteridae, Angiospermidae and the evidence for angiosperm origin

The reproductive units of the Glossopteridae are unisexual gonophylls, some with the potential for direct conversion into angiosperm flowers. Compound fructifications in both major taxa may be anthostrobili or the newly defined anthofasciculi. The enclosure of ovules in the angiosperm manner, but with extrorse orientation, places the beginning of angiospermy in the Permian. A few angiosperm gynoecia are extrorse. The presence of the leaf + branch berberoid unit is traced throughout the plant and accounts for the presence of protostelic bundles in the ventral traces and other parts of the flower. This evidence invalidates the carpel theory, but supports the gonophyll theory. The extensive evidence for relationship from reproductive organs is supported by leaf and petal venation patterns forming a continuous series linking the two taxa.     

The early evolution of the angiosperm flower

An unexpected variety of new fossil flowers from the Lower and mid-Cretaceous and new results on the structure, development and biology of the flowers of extant primitive angiosperms are leading to modifications of earlier concepts of early flower evolution. Most fossil flowers conform best to those of the angiosperm subclass Magnoliidae, diverse though they may be. The unusual variety in organ number and organ arrangement patterns is a characteristic not only of the fossils but also of the extant Magnoliidae. It is a feature of the still 'open' organization of the flower (without intricate synorganization of parts) at this evolutionary level, and not an expression of only distant phylogenetic relationship. On the other hand, many other predominant features of modern angiosperms are lacking in both earliest fossils and most extant Magnoliidae.     

Ophioglossaceae: a hypothetical archetype for the angiosperm carpel

KATO, M., 1990.Ophioglossaceae: a hypothetical archetype for the angiosperm carpel. In the light of a recently proposed phylogenetic position of Ophioglossaceae as living progymnosperms, a new archetype model for the angiosperm carpel is proposed. The three-dimensional construction of ophioglossoid fertile leaves with epiphyllous sporophores may be comparable to angiosperm carpels with adaxial ovules. The orientation of erect sporangia on young sporophores dorsiventrally facing the trophophores resembles that of anatropous ovuleS. Glossopterid fructifications may be interpreted as having the same construction as ophioglossoid leaveS. In the present hypothesis, the adaxial position of the ovules arose prior to the evolutionary process leading from gymnospermy to angiospermy. Previous hypotheses involving origins from Caytonia and Glossopteris are criticized.     

Leaf evolution in Southern Hemisphere conifers tracks the angiosperm ecological radiation

The angiosperm radiation has been linked to sharp declines in gymnosperm diversity and the virtual elimination of conifers from the tropics. The conifer family Podocarpaceae stands as an exception with highest species diversity in wet equatorial forests. It has been hypothesized that efficient light harvesting by the highly flattened leaves of several podocarp genera facilitates persistence with canopy-forming angiosperms, and the angiosperm ecological radiation may have preferentially favoured the diversification of these lineages. To test these ideas, we develop a molecular phylogeny for Podocarpaceae using Bayesian-relaxed clock methods incorporating fossil time constraints. We find several independent origins of flattened foliage types, and that these lineages have diversified predominantly through the Cenozoic and therefore among canopy-forming angiosperms. The onset of sustained foliage flattening podocarp diversification is coincident with a declining diversification rate of scale/needle-leaved lineages and also with ecological and climatic transformations linked to angiosperm foliar evolution. We demonstrate that climatic range evolution is contingent on the underlying state for leaf morphology. Taken together, our findings imply that as angiosperms came to dominate most terrestrial ecosystems, competitive interactions at the foliar level have profoundly shaped podocarp geography and as a consequence, rates of lineage diversification.     

New perspectives on the Mesozoic seed fern order Corystospermales based on attached organs from the Triassic of Antarctica

A new Triassic corystosperm is described from the Shackleton Glacier region of Antarctica. The compression fossils include cupulate organs (Umkomasia uniramia) and leaves (Dicroidium odontopteroides) attached to short shoot-bearing branches. The cupulate organs occur in groups near the apices of the short shoots, and each consists of a single axis with a pair of bracts and a subapical whorl of five to eight ovoid cupules. This unique architecture indicates that the cupules are individual megasporophylls rather than leaflets of a compound megasporophyll. A branch bearing an attached D. odontopteroides leaf provides the first unequivocal evidence that Umkomasia cupulate organs and Dicroidium leaves were produced by the same plants. Although this had previously been assumed based on organ associations, the new specimens are important in demonstrating that a single species of corystosperm produced the unique cupulate organs described here and the geographically and stratigraphically widespread and common D. odontopteroides leaf. Therefore, biostratigraphic, paleoecological, and phylogenetic studies that treat Dicroidium leaf morphospecies as proxies for biological species of entire plants should be reconsidered. Phylogenetic analysis suggests that the corystosperm cupule is an unlikely homologue for the angiosperm carpel or outer integument.     

Gene expression patterns in seed plant shoot meristems and leaves: homoplasy or homology?

The fossil record reveals that seed plant leaves evolved from ancestral lateral branch systems. Over time, the lateral branch systems evolved to become determinate, planar and eventually laminar. Considering their evolutionary histories, it is instructive to compare the developmental genetics of shoot apical meristems (SAMs) and leaves in extant seed plants. Genetic experiments in model angiosperm species have assigned functions of meristem maintenance, specification of stem cell identity, boundary formation, polarity establishment and primordium initiation to specific genes. Investigation of roles of the same or homologous genes during leaf development has revealed strikingly similar functions in leaves compared to SAMs. Specifically, the marginal blastozone that characterizes many angiosperm leaves appears to function in a manner mechanistically similar to the SAM. We argue here that the similarities may be homologous due to descent from ancestral roles in an ancestral shoot system. Molecular aspects of SAM and leaf development in gymnosperms is largely neglected and could provide insight into seed plant leaf evolution.     

Mesozoic plants and the problem of angiosperm ancestry

Krassilov, V.: Mesozoic plants and the problem of angiosperm ancestry.
Trends leading to the foliar and floral structures of angiosperms may be deduced by comparison with Mesozoic gymnosperms. The Debeya-Fontainea group of Cretaceous angiosperms closely resembles the Early Mesozoic Scoresbya group of pteridosperms with regard to leaf characters. The bivalved capsules of Jurassic Leptostrobus , with stigmatic bands, are regarded as the forerunners of certain types of angiosperm carpels. The angiospermous characters arose in several lineages of gymnosperms and were probably accumulated by non-sexual transfer of genetic material. The earliest angiosperm mega- and microfossils have been reported from the Middle and Upper Jurassic of the northern hemisphere. Most of these angiosperms were confined to chaparral-like communities dominated by shrubby conifers and cycadophytes. The rise of angiosperms was promoted by the climatic changes and the simultaneous rise of mammals.     

The morphological interpretation of epiascidiate leaves —An historical perspective—

Epiascidiate leaves are those foliar organs whose adaxial (ventral) side is the inside of a tube. Such tubular leaves are found in Nepenthaceae, Sarraceniaceae, Cephalotaceae, and Lentibulariaceae. Throughout botanical history these leaves have received considerable attention because of their bizarre morphology and problems of interpretation. This paper documents the attempts of the last 150 years to correctly understand their organographic nature. All epiascidiate foliar organs are structurally similar in their early ontogeny, each forms a distinctive adaxial outgrowth (Querzone), and the diverse morphologies of the mature organs seem to be modifications upon a similar primordial ground plan. Typologically these leaves are directly related to peltate leaves and phyllodes (non-petiolar,sensu Boke). Except for certain, highly speculative,de novo theories, such as the “foliar runner” theory of Croizat, all misinterpretations of the nature of epiascidiate leaves are directly attribuable to earlier errors in ascertaining the organography of typologically related leaf forms. Accordingly, the sympodial tubular leaf (Roth) is rejected, as is the petiolar nature of tubular leaves (de Candolle). The typological relationships of these leaves to unifacial foliar organs (Troll) seems well substantiated from both an organographic and a histogenetic viewpoint. The peltate carpel theory (?elakovský; Troll) is, in reality, an epiascidiate carpel theory. The idea of a fundamentally tubular carpel seems correct from both a typological and phylogenetic standpoint. To comprehend the various contradictory interpretations which have been used to explain morphologically complex problems, as well as to understand the genesis of morphological theories, it is necessary to acquire an accurate historical perspective of the subject.