Embryology of Swertia (Gentianaceae) relative to taxonomy

The embryological features of three species of Swertia ( s.l.) – S. erythrosticta , S. franchetiana , and S. tetraptera – were characterized, and the observations were used, together with previously gathered data on other species, to evaluate a recently proposed polyphyly, based on molecular data, of Swertia s.l. Comparisons of species within the genus showed that they have diversified embryologically, and there are significant between-species differences. Notable features that vary between species include the number of cell layers that form the anther locule wall, the construction of the wall of the mature anther, tapetum origin, the cell number in mature pollen grains, the structure of the fused margins of the two carpels, the ovule numbers in placental cross-sections, the shape of the mature embryo sac, the degree of ovule curvature, antipodal variation and the presence of a hypostase, and seed appendages. They share characters that are widely distributed in the tribe Gentianeae, such as a dicotyledonous type of anther wall formation, a glandular tapetum with uninucleate cells, simultaneous cytokinesis following the meiosis of the microsporocytes, tetrahedral microspore tetrads, superior, bicarpellary and unilocular ovaries, unitegmic and tenuinucellar ovules, Polygonum -type megagametophytes, progamous fertilization, nuclear endosperm, and Solanad-type embryogeny. The presence of variation in embryological characters amongst the species of Swertia s.l. strongly supports the view that Swertia s.l. is not a monophyletic group. Frasera is better separated from Swertia s.l. as an independent genus, and is only distantly related to Swertia s.s. judging from the numerous differences in embryology. Swertia tetraptera is very closely related to Halenia , as they show identical embryology.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 383–400.     

大钟花属和黄秦艽属花部解剖

对大钟花属和黄秦艽属进行了花部解剖学研究,并以此讨论了它们的系统演化关系。大钟花属和黄秦艽属的雌花部分花萼维管束与花冠维管束来源于同一维管束迹,而雄蕊维管束来源于雄蕊迹,每心皮具1条背维管束2条腹维管束,因此,花被维管束为融合型;黄秦艽属的雄花每个花萼、花瓣和雄蕊的维管束均来源于单个维管束迹,每心皮具1条背维管束2条腹维管束,属于基本型。从花部解剖结构看出,大钟花属与假龙胆演化支关系较近;黄秦艽属较獐牙菜属进化。     

Embryology of Plagiopteron suaveolens Griffith (Plagiopteraceae) and its systematic implications

A study of the embryology of Plagiopteron suaveolens Griffith is presented in order to evaluate the affinities of the genus. Anther wall formation is of the dicotyledonous type. The anther tapetum is glandular and its cells become two to four nucleate. Cytokinesis in the microspore mother cell is simultaneous and the resultant tetrad is tetrahedral. The mature pollen grains are two-celled. The anther has 4-locules at anthesis. The ovule is anatropous, bitegmic and weakly crassinucellate with only one cell-layered parietal tissue. The micropyle is zig-zag in section and formed by both inner and outer integuments which are three and three to four cell layers thick respectively. The megaspore archesporium is one-celled and the embryo sac development is of the Polygonum type. An endothelium is formed with early disintegration of nucellar tissue. The antipodals multiply to 15 to 20 cells. Embryological evidence supports the placement of Plagiopteron in its own family, Plagiopteraceae, with closest relationship with Celastraceae and close relationship with Elaeocarpaceae, Rhizophoraceae and some families of the Geraniales.     

Embryology of Zippelia begoniaefolia (Piperaceae) and its systematic relationships

Microsporogenesis and embryology of the monotypic Zippelia (Z. begoniaefolia) Blume (Piperaceae) is described for the first time to assess its systematic relationships. The formation of the anther wall is of Basic Type such that the anther wall, consisting of an endothecium with fibrous thickenings, two middle layers, and a glandular septum with 2‐nucleate cells, is derived from a primary parietal layer. Simultaneous cytokinesis follows meiosis of the microspore mother cell thence forming a tetrahedral tetrad of microspores. The single basal ovule is orthotropous, crassinucellate and bitegmic but only the inner integument forms the micropyle. The sporogenous cell of the nucellus functions directly as a megaspore mother cell. A coenocyte with four nuclei forms after meiosis of the megaspore mother cell. The formation of the embryo sac is tetrasporic ab initio and is of, or similar to, the Drusa Type of embryo sac in which the nuclei of the coenocyte undergo two successive mitoses and forms a 16‐celled or 16‐nucleate embryo sac that is ovoid in shape. The embryo sac has an egg apparatus consisting of an egg cell and two synergids (but one of the latter is less discernable). Two polar cells occur just beneath the egg apparatus and 11 antipodal cells or nuclei are arranged along the lower part of the inner wall of the embryo sac. They are linked by threads of cytoplasm. The two polar cells are separated or fused before fertilization. A large primary endosperm nucleus with many nucleoli, which resulted from the fertilized polar cells and with the participation of antipodal cells, divides into a free nuclei stage. The free nuclei are arranged along the lower part of the inner wall of the embryo sac or rarely assemble at the central part. The development of endosperm is thus of the Nuclear Type. The zygote remains undivided and fails to develop even when the seed is nearly mature. Frequently, the zygote and the endosperm abort later and leave an empty chamber in the top part of the seed. Most of the seed content is starchy perisperm. Only the inner integument forms the seed coat and the pericarp develops glochidiate hairs (anchor‐like hairs) when the endosperm begins to develop. By comparison with the other piperaceous taxa using embryological and botanical features, Zippelia is referred to as a basal taxon and a more isolated evolutionary line or a blind branch in the Piperaceae. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society, 2002, 140 , 49–64.     

龙胆族(龙胆科)分类与进化研究进展

龙胆是著名的高山植物,广布世界温带地区,不仅可作药用,也可用于园艺观赏。龙胆科分为6个族,其中龙胆族占龙胆科物种数的一半以上;龙胆族包括龙胆亚族和獐牙菜亚族,分类与进化方面的相关研究众多。随着分子生物学在龙胆族研究中的应用,近些年对多个类群进行了研究并发表了多个新属和新种。该文从属间和属内两个层次梳理了龙胆族近年来在分类和进化研究中的最新进展,总结了新发表的类群。并分析了现存的问题,重点强调在今后的研究中用特别注意以下几点:(1)形态性状的准确掌握对龙胆族的研究至关重要;(2)发表新类群应当谨慎;(3)单拷贝核基因有助于解析龙胆族复杂的系统发育关系;(4)关注杂交和多倍化等在龙胆族进化中的作用。     

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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Pollen morphology of the Swertiinae (Gentianaceae): phylogenetic implications

Recent molecular surveys of the Swertiinae (Gentianaceae–Gentianeae) revealed unexpected phylogenetic relationships, including polyphyly of the genera Gentianella , Jaeschkea , Lomatogonium and Swertia . To find new non-molecular characters supporting the phylogeny, we examined the exine variation of 73 species of all major lineages of subtribe Swertiinae using environmental scanning electron miscroscopy supplementing older, mainly light microscopical, studies. In contrast to previous studies, we were able to pick out taxa from phylogenetic key positions with particular focus on Swertia . Many distantly related taxa such as parts of Frasera , Gentianopsis , Halenia , Gentianella , Megacodon and several lineages of Swertia share a striate–reticulate or reticulate exine pattern. This is interpreted as the plesiomorphic character state of Swertiinae. There is also considerable variation of derived patterns; for example, different types of microechinate or almost smooth pollen was repeatedly observed in distantly related groups. Another extreme was the ring-shaped reticulation found in a North American species of Gentianopsis . Unfortunately, major relationships as revealed by molecular analyses were rarely supported because of the abundance of the plesiomorphic type and homoplasy even on low taxonomic levels; for example, within Lomatogonium . Exine variation was particularly useful in characterizing independent lineages of Swertia . For example, according to pollen characters and in agreement with other data, the Asian Swertia cuneata is a sister group of a strongly diversified African lineage and Swertia yunnanensis , which is rather aberrant in flower morphology, seems close to parts of Lomatogonium .  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 323–341.     

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     

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     

基于ITS和matK序列的獐牙菜亚族 (龙胆科龙胆族)分子系统学

为探讨獐牙菜亚族（subtribe Swertiinae）各属之间和一些属内的系统关系,本研究选取了该亚族14属68种1变种,采用最大简约法（maximum parsimony）和贝叶斯法（Bayesian inference）对样品核基因ITS和叶绿体基因matK的两个片段进行独立和联合分析。结果显示：Bartonia位于亚族的最基部;喉毛花属（Comastoma）、肋柱花属（Lomatogonium）和假龙胆属（Gentianella）都非单系,处于同一个较为进化的分支中;獐牙菜属折皱组（Swertia sect. Rugosa）和獐牙菜组（S. sect. Swertia）亲缘关系最近,宽丝组（S. sect. Platynema）和藏獐牙菜组（S. sect. Kingdon Wardia）亲缘关系最近;口药花属（Jaeschkea）与獐牙菜属多枝组（S. sect. Ophelia）的大籽獐牙菜（Smacrosperma）亲缘关系最近。同时讨论了獐牙菜亚族形态分类与分子数据不一致的原因。     

川东獐牙菜(龙胆科)的胚胎学研究

利用石蜡切片技术,对川东獐牙菜(Swertia davidii)的胚胎发育过程进行显微观察,并根据现有资料,对獐牙菜属的几种植物进行了比较胚胎学研究。结果表明:川东獐牙菜花药四室,药壁发育为基本型,绒毡层异型起源,为腺质绒毡层,发育后期药室内观察到的绒毡层核是早期该层细胞有丝分裂凸入药室并原位退化形成的,中层细胞3层,药室内壁退化,花药壁表皮宿存,细胞柱状伸长,纤维状加厚;小孢母细胞减数分裂为同时型,四分体排列方式主要为四面体形和左右对称型,少数为"T"形和十字交叉形,成熟花粉为2-细胞类型;子房2心皮、1室,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个大孢子直线形排列,合点端的大孢子具功能,雄配子体发育为蓼型;2个极核在受精前融合为1次生核,合点端3个反足细胞宿存,每个细胞均多核和异常膨大,形成明显的反足吸器,并在胚乳之外形成染色较深的类似"外胚乳"结构;珠孔受精,受精作用属于有丝分裂前类型;胚乳发育为核型,胚胎发育为茄型;果实成熟时,种子发育至心形胚阶段;反足细胞在龙胆科一些短命植物中的宿存与分裂具有重要的生殖适应与进化意义。     

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。     

Phylotranscriptomics of Swertiinae (Gentianaceae) reveals that key floral traits are not phylogenetically correlated

Establishing how lineages with similar traits are phylogenetically related remains critical for understanding the origin of biodiversity on Earth. Floral traits in plants are widely used to explore phylogenetic relationships and to delineate taxonomic groups. The subtribe Swertiinae (Gentianaceae) comprises more than 350 species with high floral diversity ranging from rotate to tubular corollas and possessing diverse nectaries. Here we performed phylogenetic analysis of 60 species from all 15 genera of the subtribe Swertiinae sensu Ho and Liu, representing the range of floral diversity, using data from the nuclear and plastid genomes. Extensive topological conflicts were present between the nuclear and plastome trees. Three of the 15 genera represented by multiple species are polyphyletic in both trees. Key floral traits including corolla type, absence or presence of lobe scales, nectary type, nectary position, and stigma type are randomly distributed in the nuclear and plastome trees without phylogenetic correlation. We also revealed the likely ancient hybrid origin of one large clade comprising 10 genera with diverse floral traits. These results highlight the complex evolutionary history of this subtribe. The phylogenies constructed here provide a basic framework for further exploring the ecological and genetic mechanisms underlying both species diversification and floral diversity.     

Variation and evolution of herkogamy in Exochaenium (Gentianaceae): implications for the evolution of distyly

Backgrounds and Aims

The spatial separation of stigmas and anthers (herkogamy) in flowering plants functions to reduce self-pollination and avoid interference between pollen dispersal and receipt. Little is known about the evolutionary relationships among the three main forms of herkogamy – approach, reverse and reciprocal herkogamy (distyly) – or about transitions to and from a non-herkogamous condition. This problem was examined in Exochaenium (Gentianaceae), a genus of African herbs that exhibits considerable variation in floral morphology, including the three forms of herkogamy.

Methods

Using maximum parsimony and maximum likelihood methods, the evolutionary history of herkogamic and non-herkogamic conditions was reconstructed from a molecular phylogeny of 15 species of Exochaenium and four outgroup taxa, based on three chloroplast regions, the nuclear ribosomal internal transcribed spacer (ITS1 and 2) and the 5·8S gene. Ancestral character states were determined and the reconstructions were used to evaluate competing models for the origin of reciprocal herkogamy.

Key results

Reciprocal herkogamy originated once in Exochaenium from an ancestor with approach herkogamy. Reverse herkogamy and the non-herkogamic condition homostyly were derived from heterostyly. Distylous species possessed pendent, slightly zygomorphic flowers, and the single transition to reverse herkogamy was associated with the hawkmoth pollination syndrome. Reductions in flower size characterized three of four independent transitions from reciprocal herkogamy to homostyly.

Conclusions

The results support Lloyd and Webb''s model in which distyly originated from an ancestor with approach herkogamy. They also demonstrate the lability of sex organ deployment and implicate pollinators, or their absence, as playing an important role in driving transitions among herkogamic and non-herkogamic conditions.     

Embryology and systematic position ofLiparis (Orchidaceae)

The embryology ofLiparis paradoxa andL. rostrata has been studied. The young anther wall consists of an epidermis, endothecium, three middle layers and secretory tapetum with uninucleate cells. In the mature anther, two or three sub-epidermal layers develop fibrous thickenings. The anther wall development corresponds to the massive type. Simultaneous cytokinesis results in decussate, isobilateral, linear, T-shaped and tetrahedral pollen tetrads. The pollinia are compact and at anthesis the pollen grains are 2-celled. Ovules are anatropous, bitegmic and tenuinucellate. Both the integuments are dermal in origin and 2-layered. Development of female gametophyte is of the monosporic, 8-nucleate type. Double fertilization occurs. The primary endosperm nucleus degenerates. The mature embryo is organized from the derivatives of tiers 1, 1, m, and n. Its development conforms to a variation of the Onagrad type. The seed coat is formed entirely by the outer layer of the outer integument. There are three sterile and three fertile valves in the ovary. In the prefertilization stages valves consist of parenchymatous cells. After fertilization, the sterile valves become sclerenchymatous whereas the fertile valves remain parenchymatous. The embryological characters support the disputed systematic position ofLiparis within subtribeLiparidinae ofEpidendreae.     

Characterization of the complete mitochondrial genome of Phodopus roborovskii (Rodentia: Cricetidae) and systematic implications for Cricetinae phylogenetics

Phodopus roborovskii (subfamily Cricetinae) is widely distributed in the northern arid regions of China. This study reports its complete mitochondrial genome (mitogenome) for the first time. The complete sequence was 16,273 bp long, including 13 protein-coding genes, 2 ribosomal RNAs, 22 transfer RNAs, and 1 major noncoding region. The base composition and codon usage were described. The putative origin of replication for the light strand (O_L) of P. roborovskii was approximately 45 bp long and was highly conserved in the stem-loop and adjacent sequences, but the starting sequence of replication varied between genera among Rodentia. We analyzed the three domains of the D-loop region, and the results indicated that the central domain had higher G + C content and lower A + T content than two peripheral domains. Phylogenetic analyses indicated high resolution in four main divergent clades using mitogenomes data within Cricetidae. Within Cricetinae clade, P. roborovskii was at basal position which was in line with previous researches, and it shared a common ancestor with other extant hamsters. This work validated previous molecular and karyotype researches using mitogenomes data, and provided a set of useful data on phylogeny and molecular evolution in Cricetidae species.     

Root Anatomy and Mycotrophy (AM) of the Achlorophyllous Voyria truncata (Standley) Standley & Steyermark (Gentianaceae)

Roots of Voyria truncata retain the primary root structure even though they can grow as thick as 2 mm in diameter. These root diameters are due to a retained capability for cell division in the cortex parenchyma. This is explained as a vital adaptation to its life form. Based on the extraradical mycelium, the mode of penetration, the structurally incompatible intraradical phase, the presence of intercellular vesicles in the root cortex, and the occurrence of immediate hyphal bridges from arbuscular mycorrhizal roots of neighbouring plants, the mycorrhiza of V. truncata is described as an arbuscular mycorrhiza (AM), although the characteristic arbuscles are missing. Special features of the AM in V. truncata are interpreted as an improved efficiency in taking advantage of the mycorrhiza. Root connections with roots of neighbouring plants are common and preferred locations for fungal infections. An evolutionary tendency towards parasitism of higher plants is discussed.     

Morphology of pollen and orbicules in the tribe Spiraeeae (Rosaceae) and its systematic implications

This study provides pollen data for 38 representative taxa belonging to all nine genera in the current classification of the tribe Spiraeeae (Rosaceae) including the monotypic Korean endemic genus Pentactina, and considers the distribution of orbicules for the first time. Pollen morphology and wall stratification were investigated using light, scanning electron and transmission electron microscopy. Spiraeeae pollen grains are small to medium in size (P = 6.9–34.0 μm, E = 7.1–28.0 μm), oblate to prolate in shape (P/E = 0.66–1.48) and tri-colporate. Spiraeeae pollen is generally characterised by striate sexine ornamentation, but four ornamentation types are recognised based on the length and direction of the ridge patterns. The observed variation in sexine ornamentation is particularly valuable at the generic level. The exine stratification of the representative Spiraeeae studied is similar and characterised by unbranched columellae and a continuous endexine. Orbicules are present in three genera of the tribe (Luetkea, Sibiraea and Xerospiraea). Orbicule distribution patterns indicate that the absence of orbicules is a synapomorphic condition of the more derived clade, comprising Pentactina + Petrophytum + Kelseya + Spiraea.     

Embryology ofKyllinga monocephala (Cyperaceae) and its systematic position

Aspects of the life history ofKyllinga monocephala are described. Anther wall development corresponds to the Monocot type. The endothecium shows spiral thickenings. The tapetum is glandular and has uninucleate cells. Ubisch granules are present. Mature pollen grains (pseudomonads) are 3-celled at maturity. Ovules are bitegmic, crassinucellate and develop a funicular obturator. The embryo development conforms to theJuncus-variation of the Onagrad type. Endosperm, seed coat and pericarp are described.