The Karyotype Analysis of Somatic Chromosomes in Amborella trichopoda (Amborellaceae)

Amborella trichopoda Baill. (Amborellaceae), which, based on multiple gene analyses, was recently identified as the first branch in the angiosperm evolution, has somatic chromosomes of 2n=26 (x=13). At metaphase all the chromosomes have centromeres at the median position. Chromosomes of one pair are longer than those of the 12 remaining pairs, and have a secondary or small constriction. Based on karyotype analysis, as well as a survey of chromosome numbers in two other earliest lineages (i.e., Nymphaeaceae and Illiciales), the x=13 of Amborella is likely to be derived from x=14. The hypothesis that x=7 is the original base number in the angiosperms was briefly discussed. Received 30 May 2000/ Accepted in revised form 22 July 2000     

Phylogeography and niche modelling of the relict plant Amborella trichopoda (Amborellaceae) reveal multiple Pleistocene refugia in New Caledonia

Amborella trichopoda Baill. (Amborellaceae, Amborellales), the sole living member of the sister group to all other extant angiosperms, is endemic to New Caledonia. We addressed the intraspecific phylogeography of Amborella by investigating whether its present population genetic structure could be related to its current and past habitats. We found moderate range‐wide genetic diversity based on nuclear microsatellite data and detected four well‐differentiated, geographically distinct genetic groups using Bayesian clustering analyses. We modelled the ecological niche of Amborella based on the current climatic and environmental conditions. The predictive ability of the model was very good throughout the Central East mainland zone, but Amborella was predicted in the northern part of the island where this plant has not been reported. Furthermore, no significant barrier was detected based on habitat suitability that could explain the genetic differentiation across the area. Conversely, we found that the main genetic clusters could be related to the distribution of the suitable habitat at the last glacial maximum (LGM, c. 21 000 years BP), when Amborella experienced a dramatic 96.5% reduction in suitable area. At least two lineages survived in distinct putative refugia located in the Massif des Lèvres and in the vicinity of Mount Aoupinié. Our findings finally confirmed the importance of LGM rainforest refugia in shaping the current intra‐ and interspecific diversity in New Caledonian plants and revealed the possibility of an as yet unreported refugium. The combination of niche modelling and population genetics thereby offered novel insight into the biogeographical history of an emblematic taxon.     

Fruit structure of Amborella trichopoda (Amborellaceae)

The indehiscent fruitlets of the apparently basalmost extant angiosperm, Amborella trichopoda, have a pericarp that is differentiated into five zones, a thin one‐cell‐layered skin (exocarp), a thick fleshy zone of 25–35 cell layers (outer mesocarp), a thick, large‐celled sclerenchymatous zone (unlignified) of 6–18 cell layers (middle mesocarp), a single cell layer with thin‐walled (silicified?) cells (inner mesocarp), and a 2–4‐cell‐layered, small‐celled sclerenchymatous zone (unlignified) derived from the inner epidermis (endocarp). The border between inner and outer mesocarp is not even but the inner mesocarp forms a network of ridges and pits; the ridges support the vascular bundles, which are situated in the outer mesocarp. In accordance with previous observations by Bailey & Swamy, no ethereal oil cells were observed in the pericarp; however, lysigenous cavities as mentioned by these authors are also lacking; they seem to be an artefact caused by re‐expanding dried fruits. The seed coat is not sclerified. The fruitlets of Amborella differ from externally similar fruits or fruitlets in other basal angiosperms, such as Austrobaileyales or Laurales, in their histology. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 148 , 265–274.     

互叶梅科系统位置评述

互叶梅科 Amborellaceae 一属一种 .形态学研究显示互叶梅 Amborella tricopoda Baill. 具有许多原始性状 .大多数最新的分子系统发育研究显示 ,互叶梅科是现存被子植物的最基部类群 .但有关互叶梅科的系统位置存在争议 .被子植物 有花植物 的起源和辐射一直是植物学家关注的热点 .本文将对该科系统位置的研究历史与现状进行评述     

Developmental morphology of the ovules of Amborella trichopoda (Amborellaceae) and Chloranthus serratus (Chloranthaceae)

The developmental morphology of the outer integument in the pendent orthotropous ovules of Amborella trichopoda (Amborellaceae) and Chloranthus serratus (Chloranthaceae) was studied. In both species the outer integument is semiannular at an early stage and becomes cup-shaped but dorsiventrally somewhat asymmetric at later stages. The outer integument, which is initiated first on the concave and lateral sides of the ovule, differs from that of the anatropous ovules of other basal families with the outer integument semiannular at an early stage or throughout development. The bilateral symmetry of the outer integument is shared by these orthotropous and anatropous ovules. The developmental pattern of the outer integument and ovule incurving characterize the ovule of the Amborellaceae and Chloranthaceae, which is not equivalent to typical orthotropous ovules of eudicots. A phylogenetic analysis of ovule characters in basal angiosperms suggests that anatropous ovules with cup-shaped outer integuments and orthotropous ovules were derived independently in several clades and that the ovules of Amborella and Chloranthus might also be derivative.     

Embryology of Laurales: a Review and Perspectives

s. str. and Siparunaceae) are probably defined by a multi-celled ovule archesporium and a crushed mesotesta. Within Laurales, 16 embryological characters are found to be diversified, including the number of microsporangia (four or two), mode of anther dehiscence (by slits or valves), the number of archesporial cells in an ovule (one, two or more), and so on. Their respective evolutions were traced on a phylogenetic tree generated from molecular and morphological data, supporting that Calycanthaceae represent the earliest branch and are sister to a clade comprising six remaining families with a valvate anther dehiscence as already suggested. However, because of a lack of sufficient data from each family of Laurales, embryological characters often have alternative possibilities with respect to where they have evolved. More extensive and/or intensive studies of individual families are needed to clarify their exact evolutionary relationships. Received 19 March 2001/ Accepted in revised form 6 June 2001     

Amborella trichopoda (Amborellaceae) and the evolutionary developmental origins of the angiosperm progamic phase

A remarkable number of the defining features of flowering plants are expressed during the life history stage between pollination and fertilization. Hand pollinations of Amborella trichopoda (Amborellaceae) in New Caledonia show that when the stigma is first receptive, the female gametophyte is near maturity. Pollen germinates within 2 h, and pollen tubes with callose walls and plugs grow entirely within secretions from stigma to stylar canal and ovarian cavity. Pollen tubes enter the micropyle within 14 h, and double fertilization occurs within 24 h. Hundreds of pollen tubes grow to the base of the stigma, but few enter the open stylar canal. New data from Amborella, combined with a review of fertilization biology of other early-divergent angiosperms, show that an evolutionary transition from slow reproduction to rapid reproduction occurred early in angiosperm history. I identify increased pollen tube growth rates within novel secretory carpel tissues as the primary mechanism for such a shift. The opportunity for prezygotic selection through interactions with the stigma is also an important innovation. Pollen tube wall construction and substantial modifications of the ovule and its associated structures greatly facilitated a new kind of reproductive biology.     

条纹龙胆的胚胎学研究

首次报道了条纹龙胆（Ｇｅｎｔｉａｎａ ｔｓｒｉａｔａ Ｍａｘｉｍ．）的胚胎学特征,研究结果用以讨论龙胆属狭蕊组（Ｇｅｎｔｉａｎａ Ｓｅｃｔ．Ｓｔｅｎｏｇｙｎｅ）的系统演化关系。主要研究结果如下：花药四室;药壁发育为双子叶型;绒毡层细胞仅来源于初生壁细胞,故绒毡层起源属单型起源,细胞单核,原位退化,属腺质型绒毡层,药隔处的绒毡层细胞经多次平周分裂形成２层至多层的绒毡层细胞,其余部位的绒毡层细胞仍为１     

峨眉双蝴蝶的胚胎学研究

首次报道了峨眉双蝴蝶Ｔｒｉｐｔｅｒｏｓｐｅｒｍｕｍ ｃｏｒｄａｔｕｍ（Ｍａｒｑ．）Ｈ．Ｓｍｉｔｈ的胚胎学特征,研究结果用以讨论双蝴蝶属的系统演化关系。主要研究结果如下：花药四室;药壁发育为双子叶型;绒毡层属单型起源,细胞具单核,属腺质型绒毡层,药隔处的绒毡层细胞形成类胎座,其余部位的绒毡层细胞仍为一层细胞;在花药成熟时,花药的药室内壁纤维状如厚且柱状伸长,表皮细胞减缩退化,纤维状加厚不明显。成熟花     

嵩草属植物的胚胎学

对嵩草属（ Ｋｏｂｒｅｓｉａ） 植物进行了初步的胚胎学研究。该属植物具假四合花粉（ｐｓｅｕｄｏｍｏｎａｄ） ; 药室内壁在二核花粉时期开始螺旋状加厚, 花药表皮在花粉成熟时形成乳突; 成熟花粉具三细胞。胚珠为倒生型, 具厚珠心和双层珠被, 珠孔由内珠被构成, 珠柄的近基部向珠孔增生形成珠孔塞。胚囊的发育为蓼型, 四分体线形排列, 合点端大孢子发育成八核胚囊。受精后, 胚乳核先于受精卵进行分裂, 胚乳的发育为核型。胚的发育为柳叶菜型灯芯草变型。通过比较, 嵩草属植物大小孢子的发育、胚珠的结构、胚囊的发育、胚乳的发育和胚的发育与莎草科中其它类群一致。所以, 根据胚胎学资料, 嵩草属及其近缘属应保留在莎草科中,不该另立为嵩草科。     

Embryology of Gomortegaceae (Laurales): characteristics and character evolution

The embryological characteristics of Gomortegaceae, which are poorly understood, were investigated on the basis of Gomortega nitida, the only species of the family, to understand better the evolution of this group within Laurales. Comparisons with other Laurales and Magnoliales (a sister group of Laurales) show that Gomortega has many embryological features in common with the other lauralean families. Notably, Gomortega shares a testa without or with at best only a poorly developed mesotesta as a synapomorphy with all other Laurales. The genus further shares anthers dehisced by valves as a synapomorphy with the other Laurales (except for Calycanthaceae and Monimiaceae), and a non-multiplicative testa and bisporangiate anther as synapomorphies with Atherospermataceae and Siparunaceae (although the non-multiplicative testa occurs as a homoplasy in Monimiaceae, and the bisporangiate anther in Monimiaceae pro parte, Lauraceae pro parte and Hernandiaceae, respectively). Gomortega shows simultaneous cytokinesis to form pollen grains, a one-celled ovule archesporium and non-specialized chalaza, all or part of which may be synapomorphies shared with Atherospermataceae. Gomortega appears to have no embryological autapomorphies, but further comparison with Atherospermataceae is required.Kweon Heo and Yukitoshi Kimoto contributed equally to this work.     

四数獐牙菜的胚胎学及其系统学意义

四数獐牙菜花药四室,药壁发育为双子叶型;绒毡层腺质型。小孢子母细胞减数分裂为同时型, 四分体的排列方式为四面体形;成熟花粉为3-细胞。子房2心皮,2心皮连接处强烈内凸,4列胚珠。薄 珠心,单珠被,直生胚珠。胚囊发育为蓼型。胚乳发育为核型。胚胎发育为茄型酸浆I变型。反足细胞 在胚囊成熟时期宿存。果实成熟时,种子只发育至球型胚阶段。承珠盘存在。与已研究的獐牙菜种类 的胚胎特征相比较,该种存在三个显著的特点：直生胚珠,心皮连接处强烈内凸,承珠盘存在。这三个特 征目前仅在龙胆族中的花锚属中发现。经过性状分析,它们均是演征,此三个共有演征表明四数獐牙菜 与花锚属是一单系群,它们的亲缘关系最近。这与Yun &; Kupfer(1995)的分子证据部分吻合,因为分 子系统树上的花锚单系支包括花锚、四数獐牙菜和北美的密花属(广义獐牙菜属中的密花组),而后者的 胚胎学特征未有任何报道。胚胎学研究暗示四数獐牙菜的分类学等级有待重新评价,广义的獐牙菜属 有可能不是一单系发生群。     

Embryology of Swertia tetraptera Maxim. (Gentianaceae) and its systematic implication

The embryology of Swertia tetraptera is reported for the first time. The anther is tetrasporangiate and its wall, of which the development conforms to the dicotyledonous type, is composed of epidermis, endothecium, middle layer and tapetum at the mature stage. The tapetum has dual origin and is similar to the glandular type. Cytokinesis is of the simultaneous type and microspore tetrads are mostly tetrahedral. Pollen grains are mostly 3-celled when shed. The ovary is bicarpellate and unilocular with four series of ovules. The fused margins of two carpels intensively protrude into the locule. The ovule is unitegmic, tenuinucellate and orthotropous. The development of embryo sac is of the Polygonum type. The development of endosperm conforms to the nuclear type and the embryogeny corresponds with the Physalis I variation of Solanad type. Three antipodal cells persist at the mature embryo sac. The embryo is at the globular stage when seeds are released from the capsule. Compared with the other studied species in Swertia, S. tetraptera shows differences from them in three distinctive embryological traits: enlargement and protrusion of the fused margins of two carpels into the ovary locule; orthotropous ovules and a developed hypostase. These three characters were previously only found in the genus Halenia of the tribe Gentianinae in the Gentianaceae,and thus suggest that S. tetraptera should be related to Halenia. The results partly correspond with the molecular evidence (Yuan & Kupfer, 1995). The monophyletic Halenia clade in Yuan & Kupfer's molecular cladogram includes Halenia, S. tetraptera and Frasera (section Frasera in Swertia s. l.); nevertheless, up to now, no embryological study on Frasera has been reported. The embryological results imply that the taxonomic status of S. tetraptera needs to be revaluated and the genus Swertia s. l. may not be a mono-phyletic group. Decontaminated thianthrene disproportion. 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西南獐牙菜的胚胎学及其系统学意义

报道了西南獐牙菜的大、小孢子发生及雌,雄配子体发育过程,并以此讨论了獐牙菜属宽丝组和多枝组的分类等级和系统演化关系,西南獐牙菜花药四室;药壁发育为双子叶型;绒毡层二型起源,腺质型;中层细胞2层;药室内壁纤维状加厚,药壁表皮宿存,小孢子母细胞减数分裂为同时型;小孢子四分体的排列为四面体形,成熟花粉为3-细胞型,孔子房为3心皮,1室,胚珠12列,故为超侧膜胎座,薄珠心,单珠被,倒弯生胚珠,大孢子母细胞减数分裂形成4个大孢子呈直线形排列,合点端的大孢子具功能,胚囊发育为蓼型,两极核在受精前融合为次生核,3个反足细胞次生增殖为5-8个,宿存,比较宽丝组和多枝组的胚胎党性一状表明宽丝组从多枝组中分出是合理的,在系统位置上宽丝组较多枝组进化。     

Embryology ofCrocus thomasii (Iridaceae)

The embryology ofCrocus thomasii is described. Male meiosis is of simultaneous type, and gives rise to starchy microspores which develop into lipoid pollen grains; these are two-celled and show a spinulate acolpate, abaculate exine lacking apertures. The tapetum is glandular and its cells become bi- or sometimes multinucleate. The ovule is anatropous and bitegmic; the inner integument forms the micropyle. Megasporogenesis is heteropolar with starch accumulation in the functional chalazal megaspore. Embryo sac development conforms to thePolygonum type. The endosperm development is nuclear. The embryo develops according to the Caryophyllad type. In the ripe seed it is differentiated and enveloped by a starchy cellular endosperm. The embryological characters observed strongly favour a close relation betweenC. thomasii andC. sativus.     

Embryology of Siparunaceae (Laurales): characteristics and character evolution

Embryological characters of Siparunaceae, which are poorly understood, were studied on the basis of two constituent genera, an African Glossocalyx and a South American Siparuna, to better understand their evolution within Laurales. These two genera have many embryological characteristics in common with the other lauralean families. Noticeably, they share the multi-celled ovule archesporium (uncertain in Glossocalyx) as a synapomorphy with all the other lauralean families except Lauraceae, the anthers dehisced by valves as a synspomorphy with all the other lauralean families except Calycanthaceae and Monimiaceae, and the bisporangiate anther as a synapomorphy with Gomortegaceae and Atherospermataceae. Siparunaceae are, however, distinct from all other laularean families in having unitegmic ovules that were derived from bitegmic ovules, probably due to an elimination of the outer integument. Likewise, the lack of the testa (i.e., developed outer integument), the "endotegmic" seed coat, and the perichalazal seed at maturity are also characteristics of Siparunaceae. Within the family, Siparuna differs from Glossocalyx in having plural tetrads of megaspores and plural, starchy-rich, one-nucleate, tubular embryo sacs (autapomorphies). On the other hand, Glossocalyx is characterized by having bilaterally flattened seeds (autapomorphy). Although functional aspects of those autapomorphies are uncertain, both Glossocalyx and Siparuna show evolution in different embryological characters.     

Embryology ofEriocaulon setaceum (Eriocaulaceae)

Eriocaulon setaceum can be characterized by: young microsporangium wall with epidermis, endothecium (with fibrous thickenings), and glandular tapetum (uninucleate cells); pollen grains 3-celled, spiraperturate; embryo sac development according to the Polygonum type and with antipodal cyst; endosperm nuclear; embryo small, with incipient differentiation into cotyledonary and epicotylary loci; seed coat mainly from the inner layers of the integuments; pericarp 2-layered and membranous. Embryologically, theEriocaulaceae are nearer to theXyridaceae than to otherFarinosae. Their elevation to the rank of an order,Eriocaulales, therefore appears justified.     

Embryology and relationships ofSuriana maritima L. (Surianaceae)

An intensive study of the embryology ofSuriana maritima L. is made to provide the information for discussing relationships and systematic position of the genus which is uncertain yet. Notable embryological features ofSuriana include: ovular archesporium multi-celled; ovule unitegmic, campylotropous, and crassinucellate with a nucellar cap; obturator not formed; ovule and seed pachychalazal; chalazal haustorium of endosperm formed; mature seed exalbuminous. Comparisons with possibly related families suggest thatSuriana is distinct from any of the families discussed but best resembles Rutaceae (and Simaroubaceae). Until a study onStylobasium and several other genera, which might be closer toSuriana, comes up in future, we tentatively support the placement ofSuriana as a monotypic family Surianaceae in Rutalessens. Takhtajan.