Ovules and seeds in Euphorbioideae (Euphorbiaceae): structure and systematic implications

Ovule and seed structure in Euphorbioideae, one of the five euphorbiaceous subfamilies, is surveyed to evaluate its systematic implications on the basis of 79 species representing four of five tribes. All Euphorbioideae, like two other "uniovulate" subfamilies Acalyphoideae and Crotonoideae, but unlike most of two "biovulate" subfamilies Oldfieldioideae and Phyllanthoideae, consistently have a persistent and palisadal exotegmen composed of radially elongate, sclerotic, and pitted cells. Within Euphorbioideae, the tribe Stomatocalyceae (also with the palisadal exotegmen) is unusual in having vascular bundles in outer integument and clearly distinct from the remaining Euphorbioideae and the other "uniovulate" subfamilies. With the exclusion of Stomatocalyceae, Euphorbioideae are not anatomically divided into major groups such as a pseudanthial and a non-pseudanthial clade, but instead have some remarkable diversity within a tribe, a subtribe, and even a genus in the three ovule and seed characters: (1) the thickness of the inner integument, (2) the thickness of the outer integument, and (3) the presence or absence of an aril. Groups of genera and species wrapped by different combinations of their characteristics, however, are not necessarily harmonized with tribal or subtribal classifications available. Anatomical similarities and dissimilarities presented in this paper, as well as relationships among taxa presented in the classifications available, will be critically evaluated in the light of results of ongoing molecular phylogenetic analyses. Electronic Publication     

Ovules and seeds in Acalyphoideae (Euphorbiaceae): structure and systematic implications

Acalyphoideae, the largest subfamily of Euphorbiaceae, are investigated with respect to ovule and seed structure on the basis of 172 species of 80 genera in all 20 tribes of Acalyphoideae sensu Webster. All species of Acalyphoideae examined have bitegmic ovules with a non-vascularized inner integument. However, noticeable differences exist among and sometimes within the genera in the thickness of the inner and outer integument, the presence or absence of vascular bundles in the outer integument, whether ovules are pachychalazal or not, the presence or absence of an aril, seed coat structure (in terms of the best-developed mechanical cell-layer), and the shape of cells constituting the exotegmen. For the latter two characters, two different types of seed coat (i.e., "exotegmic" and "exotestal") and three different types of exotegmic cell (i.e., palisadal, tracheoidal and ribbon-like) were distinguished. Comparisons showed that three tribes Clutieae, Chaetocarpeae and Pereae are distinct from the other Acalyphoideae as well as from the other Euphorbiaceae in having an exotestal seed coat with a tracheoidal exotegmen. The tribe Dicoelieae is also distinct from the other Acalyphoideae in having an exotegmic seed that is composed of ribbon-like cells of exotegmen (i.e., cells both longitudinally and radially elongated, sclerotic and pitted). The tribe Galearieae, which should be treated as a distinct family Pandaceae, is also distinct from the other Acalyphoideae in having an exotegmic seed with a tracheoidal exotegmen (i.e., cells longitudinally elongated, sclerotic and pitted). The remaining genera of Acalyphoideae always have an exotegmic seed with a palisadal exotegmen (i.e., cells radially elongated, sclerotic and pitted). The shared palisadal exotegmen supports the close affinity of Acalyphoideae (excluding five tribes) with Crotonoideae and Euphorbioideae. Within the remaining genera of Acalyphoideae, a significant diversity is found in ovule and seed morphology with respect to the thickness of the inner and outer integument, the size of chalaza, vascularization of an outer integument and an aril.     

秋枫属的染色体数目及其进化意义

对秋枫属两个种Bischofia javanica和B·polycarpa的体细胞进行了染色体计数研究。结果表明这两个种在形态学上虽然存在差异,如秋枫是圆椎花序,重阳木是总状花序,但染色体数目均为2n=196。同时,结合细胞学、形态学和生态学特点探讨了秋枫属的染色体基数,多倍化的起源及其演化意义。     

Development of Ovules and Embryo sacs in Ostrya virginiana (Betulaceae) and Its Systematic Significance

The development of ovules and embryo sacs in Ostrya virginiana was studied for the first time. Most ovaries had two ovules which were anatropous, unitegmic and crassinucellate. The ovule usually possessed several archesporial ceils which divided periclinally into the upper parietal cell and the lower sporogenous cell. The sporogenous cell functioned directly as megaspore mother cell. The tetrad of megaspores was linear in arrangement, and every megaspore might be functional. One ovule often contained 2- 6 embryo sacs and the embryo sac belongs to Polygonum type. It can be concluded from the present data that all ovules among the genera of the Betulaceae are unitegrnic. There are more groups with the phenomenon of multiple embryo sacs in anemophic plants such as Betulaceae, Casuarinaceae, Graminae, Jnglandaceae, Myricaceae, Simaroubaceae, Ulmaceae, than in entomophilous plants. Multiple embryo sacs also occur among some parasitic plants and saprophytes, e.g. Orobanchaceae, Cassytha in Lauraceae, Cuscuta in Convolvulaceae and Utricularia in Lentibulariaceae. It may be inferred that the characteristic of multiple embryo sacs be an evolutionary adaptation of those plants with lower pollination rate to increase the rate of fertilization. Finally, a comparison of embryological characters among the genera of the Betulaceae shows that the family is of a number of common embryological characters, such as multicellular archesporium, multiple embryo sacs in one ovule, and a long interval between pollination and fertilization. The diversity and systematic significance of several embryological characters among the “higher” hamamelid families are also discussed. It is still hard to explain the phy-logenetic relationships among those families clearly only with.     

大戟科叶下珠属花粉形态的研究

对叶下珠属Phyllanthus Linn.13种植物花粉进行了光学显微镜和扫描电镜的观察。研究表明,本属花粉虽然在大小、形状和外壁纹饰等方面有不同程度的差异,但差异最大的还是在于萌发孔类型上。可以把本属花粉分为3孔沟,4－5孔沟,多孔沟,散沟（沟短而纺锤形或近圆形）和散孔等类型。这些萌发孔类型虽然与李秉滔在中国植物志第44卷中所划分的组不很吻合,但或多或少有一定的相关性,并且对于属下的分类具有一定的意义。在外壁纹饰方面,均为网状纹饰,可分为具粗网眼,细网眼和中等网眼等几种类型。但纹饰类型在组间或种间的差异不大明显。     

Functional andromonoecy in Euphorbia (Euphorbiaceae)

The occurrence of cyathia containing staminate flowers but lacking a pistillate flower was studied in 17 species of Euphorbia. Male cyathia were found in the majority of species studied (88.2%) giving functional andromonoecy. In the male cyathia, the pistillate flower is generally totally absent, but sometimes a vestigial pistillate flower with a non-functional ovary is present. The proportion of male cyathia varied at both the population and species level. The position of male cyathia within the inflorescence showed a constant pattern among species: the proportion of male cyathia decreased from the first to the last levels of the pleiochasia. In general, perennial species had significantly higher proportions of male cyathia than annual species (mean 20 and 2.3%, respectively). In annual species there was a trend for production of male cyathia only in the first level of the inflorescence, whereas in perennials production up to the fourth level of the inflorescence was usual. Functional andromonoecy is common in Euphorbia and represents a new sex segregation in the genus. The selective forces causing this secondary sex segregation in Euphorbia, such as improved pollination or increased outcrossing, are discussed.     

Embryology of <Emphasis Type="Italic">Japonolirion</Emphasis> (Petrosaviaceae,Petrosaviales): a comparison with other monocots

Japonolirion osense, the sole species of the genus, endemic to Japan, which is placed together with Petrosavia in the Petrosaviaceae and the order Petrosaviales, is still poorly known with respect to systematic characters. Here I present an embryological study of the anther, ovule, and seed of J. osense. Japonolirion is characterized by a glandular anther tapetum, simultaneous cytokinesis in the microspore mother cell, two-celled mature pollen grains, anatropous and crassinucellate ovules, a two-cell-layered nucellar cap formed early in ovule development, antipodal cells hypertrophied in post-fertilization stages, the ab initio cellular mode of endosperm formation, and exotegmic seeds. Comparisons with the basal monocots Acorus (Acorales) and Araceae (Alismatales), and with the more derived monocots Nartheciaceae (Dioscoreales) and Velloziaceae/Triuridaceae (Pandanales), showed that Japonolirion is clearly distinct from those basal and more derived monocots, supporting a distinct position for Petrosaviaceae or Petrosaviales within the monocots. Extensive comparisons further suggest that the two-cell-layered nucellar cap, whose cells are rich in cytoplasm at the time of fertilization in Japonolirion and thus obviously function as the obturator, is likely to be a common characteristic of the basal monocots and may even be a link with the magnoliids.     

Pedilanthus diazlunanus (Euphorbiaceae): pollination by hymenopterans in a bird-pollinated genus

Pollination in the genus Pedilanthus is commonly effected by hummingbirds. Pollination by vespid wasps in Pedilanthus is documented for the first time based on observations of Pachodynerus nasidens and Eumenes americanus pollinating Pedilanthus diazlunanus. An hypothesis concerning the mechanism by which hummingbird pollination was replaced by insect pollination in Pedilanthus is advanced based on observations of insects on P. bracteatus.     

Pollen morphology of Trigonostemon and its relatives (Euphorbiaceae)

The pollen of Trigonostemon and the related genera Dimorphocalyx, Ostodes, Tritaxis and Jatropha (outgroup) has been studied with light microscopy, and scanning and transmission electron microscopy. The two major pollen types within Trigonostemon correlate well with macromorphological characters. Species belonging to the Trigonostemon reidioides type have pollen with ‘croton pattern’ ornamentation, a pistil with deeply divided stigmas (to at least half the length of the stigma arm) and stamens with a protruding appendage on the connective, while species of the Trigonostemon verrucosus type have verrucate (to almost gemmate) pollen, stigmas that are shortly cleft and stamens without an appendage on the connective. Dimorphocalyx, Ostodes, Tritaxis and Jatropha (outgroup) have similar pollen morphology, while Trigonostemon deviates from these genera in the absence of the ‘vertically’ striate ornamentation on the subunits. Therefore, when compared with an existing phylogeny of the Euphorbiaceae, the pollen characters of Trigonostemon appear to be derived. Moreover, because the ‘croton pattern’ ornamentation itself is widely shared by the ‘inaperturate crotonoids’, the loss of that structure in the Trigonostemon verrucosus type pollen is considered a further apomorphy.     

灰岩粗毛藤(大戟科)——广东省一新记录种

报道在深圳市龙岗区排牙山求水岭发现的1个广东省新记录种--大戟科粗毛藤属灰岩粗毛藤Cnesmone tonkinensis (Gagnep.) Croiz.,并对该种的形态、生境、所在群落的特征等进行描述。该标本的采集地排牙山是其分布的最东界。     

Evolution of myrmecophytism in western Malesian Macaranga (Euphorbiaceae)

Plants inhabited by ants (myrmecophytes) have evolved in a diversity of tropical plant lineages. Macaranga includes approximately 300 paleotropical tree species; in western Malesia there are 26 myrmecophytic species that vary in morphological specializations for ant association. The origin and diversification of myrmecophytism in Macaranga was investigated using phylogenetic analyses of morphological and nuclear ITS DNA characters and studies of character evolution. Despite low ITS variation, the combined analysis resulted in a well-supported hypothesis of relationships. Mapping myrmecophytism on all most parsimonious trees resulting from the combined analysis indicated that the trait evolved independently between two and four times and was lost between one and three times (five changes). This hypothesis was robust when tested against trees constrained to have three or fewer evolutionary transformations, although increased taxon sampling for the ITS analysis is required to confirm this. Mapping morphological traits on the phylogeny indicated that myrmecophytism was not homologous among lineages; each independent origin involved a suite of different specializations for ant-plant association. There was no evidence that myrmecophytic traits underwent sequential change through evolution; self-hollowing domatia evolved independently from ant-excavated domatia, and different food-body production types evolved in different lineages. The multiple origins of myrmecophytism in Macaranga were restricted to one small, exclusively western Malesian lineage of an otherwise large and nonmyrmecophytic genus. Although the evolution of aggregated food-body production and the formation of domatia coincided with the evolution of myrmecophytism in all cases, several morphological, ecological, and biogeographic factors appear to have facilitated and constrained this radiation of ant-plants.     

Chemotaxonomy of the tribe Antidesmeae (Euphorbiaceae): antidesmone and related compounds

Selected species of the tribe Antidesmeae (Euphorbiaceae, subfamily Phyllanthoideae) have been screened for antidesmone occurrence and its content by quantitative HPLC (UV) and qualitative LC-MS/MS analysis. The LC-MS analysis allowing the additional detection of 17,18-bis-nor-antidesmone, 18-nor-antidesmone, 8-dihydroantidesmone and 8-deoxoantidesmone was carried out in the selected reaction monitoring (SRM) mode. Leaf material from herbarium specimens of 13 Antidesma spp., Hyeronima alchorneoides and Thecacoris stenopetala (all subtribe Antidesminae), as well as Maesobotrya barteri, Aporosa octandra (both Scepinae) and Uapaca robynsii (Uapacinae) were analysed. Additionally, freshly collected samples of different plant parts of two Antidesma spp. were investigated to ensure the significance of the results on herbarium specimens and to compare the antidesmone content in bark, root and leaves. Antidesmone could be unambiguously identified in 12 of 13 Antidesma spp., as well as in the two other investigated genera of subtribe Antidesminae, in levels of up to 65 mg/kg plant dry weight. Antidesmone was not found in specimens from other subtribes. Antidesmone-derived compounds occur in much lower concentrations than antidesmone.     

Ovules and seeds ofDirachma socotrana (Dirachmaceae)

Dirachma has a bitegmic, crassinucellate and anatropous ovule with a single median provascular tegumentary bundle. The seed coat is characterized by an exotesta and an endotegmic pigment layer. Although the fruit ofDirachma superficially resembles that of theGeraniaceae s. str., the characters of ovule and seed do not support a relationship with that family. Also a relationship withBarbeyaceae, as suggested by recentrbcL studies, is not supported by seed anatomical characters. The true relationships ofDirachma are difficult to assess on the basis of ovule and seed characters alone. TheRhamnaceae may be a closer relative.     

山地五月茶的蝇类传粉研究

观测了山地五月茶Antidesma montanum的开花物候、开花动态、访花者种类和访花行为,并对其繁育系统、花粉组织化学、花粉胚珠比（P／O）、花粉活力进行了检测。结果表明：山地五月茶是雌雄异株植物;其总状花序花期可长达7天;雄花／雌花花序数目为140．33±27．79／208．33±33．65（n=6）,雌雄花的颜色为很淡的黄绿色小型花;雄花单花花期为2天,花药开裂当天有活力,花粉为非淀粉型,花粉胚珠比为3333．33±607．18;单花花蜜量可达0．34±0．03μL,花蜜含糖量3．69％±0．30％。花的结构和开花式样适合蝇类传粉。芳香的气味是吸引蝇类的直接物质：花蜜是传粉者的报酬。主要的传粉昆虫为双翅目Diptera丽蝇科Calliphoridae的Chrysomya megacephala、Chrysomyasp．、寄蝇科Tachinidae的Drino sp．和蝇科Muscidae的Spilogona sp．、Mitroplatia sp．。套网不授粉的处理不结实,表明山地五月茶不存在无融合生殖,人工辅助授粉的坐果率（39．1％）略高于自然坐果率（36．7％）,二者无显著差异,表明其坐果率主要受自身资源分配限制。还讨论了蝇类传粉与雌雄异株性系统以及蝇类传粉与热带林中小型黄绿色花植物的相关性。     

中国大戟属13种15个居群的核型报道

对国产大戟科Euphorbiaceae大戟属Euphorbia的13种15个地方居群的核型进行研究, 以期为解决该属的种间亲缘关系和物种进化机制提供依据。结果如下: 地锦E. humifusa (望江居群), 2n=2x=22=20m (2SAT)+2sm; 地锦E. humifusa (红旗村居群), 2n=2x=22=18m+4sm; 千根草E. thymifolia, 2n=4x=40=40m; 斑地锦E. maculata, 2n=4x=40=36m+4sm; 银边翠E. marginata, 2n=8x=56=40m+ 8sm+8st; 铁海棠E. milii, 2n=4x=40=32m+8sm; 金刚纂E. neriifolia, 2n=6x=60=6m+36sm+12st+6t; 火殃勒E. antiquorum, 2n=6x=60=24m+24sm+12st; 一品红E. pulcherrima, 2n=4x=28=24m(3SAT)+4sm; 猩猩草E. cyathophora, 2n=4x=28=16m+12sm; 齿裂大戟E. dentata, 2n=4x=28=28m; 续随子E. lathyris, 2n=2x=20=12m+8sm; 泽漆E. helioscopia, 2n=6x=42=36m+6sm; 乳浆大戟E. esula (陈家沟居群), 2n=2x=20=14m+6sm; 乳浆大戟E. esula (樱桃沟居群), 2n=4x=40=32m+8sm。千根草和斑地锦两个种的核型以及乳浆大戟的四倍体居群核型均为首次报道。     

Patterns of asymmetry in the twining vine Dalechampia scandens (Euphorbiaceae): ontogenetic and hierarchical perspectives

We studied patterns of fluctuating asymmetry (FA) in leaves of four populations of the neotropical vine Dalechampia scandens to obtain insight into the origin of leaf FA and the level at which it is controlled. We analysed correlations in signed and unsigned asymmetry at different organizational levels. We also analysed the ontogeny of FA during leaf expansion to test whether asymmetry is regulated during cell expansion, and whether fast-expanding leaves are more or less asymmetrical. Signed asymmetry was negatively correlated between successive leaves, that is, when the right side of a leaf was larger than the left side, the next leaf on the shoot tended to show the opposite pattern. The magnitude of FA, however, was very weakly correlated among successive leaves or among leaves measured on different shoots. The direction of asymmetry did not change during leaf expansion, but the relative asymmetry, that is, asymmetry corrected for difference in trait size, decreased during expansion. We found a weak negative relationship between leaf expansion rate and relative asymmetry on the fully expanded leaves. These results suggest that leaf asymmetry in Dalechampia originates from perturbations in cell proliferation in the stem, creating asymmetries in opposite directions in successive leaves. These asymmetries persist during leaf expansion, but tend to be reduced by unknown mechanisms.     

Diterpenoids from Neoboutonia glabrescens (Euphorbiaceae)

Glabrescin, a daphnane diterpenoid, neoboutonin, a degraded diterpenoid with a novel skeleton, and neoglabrescins A and B, two rhamnofolane derivatives, have been isolated from the stem bark of Neoboutonia glabrescens Prain (Euphorbiaceae), together with the known tigliane derivative, baliospermin, and the known daphnane, montanin. Other constituents include squalene, 3-acetylaleuritolic acid, oleanolic acid and sitosterol, and the phenolic compounds 9-methoxy-1,7-dimethylphenanthrene and 2,3,8-tri-O-methylellagic acid. The structures were assigned on the basis of spectral studies and comparison with published literature data. The structures of neoglabrescins A and B were derived for their acetylated derivatives and, in the case of neoglabrescin A, confirmed by X-ray crystallographic analysis.     

Chromosome and breeding system evolution of the genus Mercurialis (Euphorbiaceae): implications of ITS molecular phylogeny

 The internal transcribed spacers (ITS1 and ITS2) of nuclear ribosomal DNA were amplified and sequenced from 19 samples representing all species of the genus Mercurialis and two outgroup species, Ricinus communis and Acalypha hispida. The length of ITS1 in the ingroups ranged from 223 to 246 bp and ITS2 from 210 to 218 bp. Sequence divergence between pairs of species ranged from 1.15% to 25.88% among the ingroup species in the combined data of ITS1 and ITS2. Heuristic phylogenetic analyses using Fitch parsimony on the combined data of ITS1 and ITS2 with gaps treated as missing generated 45 equally parsimonious trees. The strict consensus tree was principally concordant with morphological classification. Within the genus, the ITS sequences recognised two main infrageneric clades: the M. perennis complex including three Eurasian stoloniferous species (M.␣leiocarpa, M. ovata and M. perennis) and the western Mediterranean group including eight both annual and perennial species. Of the western Mediterranean clade, the annual and perennial species grouped respectively into two different groups, and the annual life form is revealed as a synapomorphic character derived from perennial, whereas in the Eurasian clade ITS phylogeny suggested M. leiocarpa as basal clade sister to M.␣perennis and M. ovata. ITS phylogeny failed to resolve the relationships among the different cytotypes of M. ovata and M. perennis. ITS phylogeny also suggested rapid karyotypic evolution for the genus. The karyotypic divergence among the perennial species of western Mediterranean region did not corroborate the nucleotide sequence divergence among the species. Optimisation of chromosome numbers onto the ITS phylogeny suggested x=8 to be the ancestral basic chromosome number of the genus. ITS phylogeny confirmed that the androdioecy of M. ambigua is derived from dioecy. The nucleotide heterozygosity and additivity in ITS sequences clearly confirm the interspecific hybridisation in the genus Mercurialis. Received December 22, 2001; accepted May 21, 2002?Published online: November 14, 2002 Address of the authors: Martin Kr?henbühl, Yong-Ming Yuan (correspondence) and Philippe Küpfer, Institut de Botanique, Laboratoire de botanique évolutive, Université de Neuchatel, Emile-Argand 11, CH-2007 Neuchatel, Suisse. (e-mail: yong-ming.yuan@unine.ch)