Flower development inAntirrhinum majus L. (Scrophulariaceae) with a comment upon corolla tube formation

The inflorescence apex is stratified and has a single layered tunica, bracts as well as all the floral organs develop acropetally. Except for stamens which are initiated with the activity of deeper layers of apex, all other floral appendages are initiated with the activity of second layer. On the basis of ontogenetic studies the floral organs have been homologised with the leaves. The adjacent calyx lobes develop and remain closely appressed and do not show post-genital fusion. Corolla tube is formed due to zonal growth preceeded by joint growth of hump on the abaxial face of stamen primordia and interprimordial region between petal primordia. Thus no post-genital fusion was observed. The placentae develop concomitantly with carpellary wall.     

Floral development in Astragalus caspicus Bieb. (Leguminosae: Papilionoideae: Galegeae)

Floral organogenesis and development of the bushy perennial legume Astragalus caspicus were studied using epi-illumination light microscopy techniques. Based on our observations, flowers are in axillary two-flowered racemes, initiate all 21 floral organs and show precocious appearance of zygomorphy. The order of floral organ initiation is unidirectional in whorls starting from the abaxial position of the flower with a high degree of overlap. Another important ontogenetic feature is the existence of two successive common primordial stages categorized as primary and secondary. The primary common primordia produce antesepalous stamens and secondary common primordia. In contrast, the five secondary common primordia subdivide into a petal and an antepetalous stamen primordia. Our findings on floral ontogeny of A. caspicus provide new evidence for the complex and variable floral initiation and development in legumes. The floral apex with strong overlapping initiation of different organs illustrates a paradox in which different capabilities must be presumed to exist simultaneously. Moreover, two extraordinary types of common primordia represent possibly an advanced evolutionary trend where time intervals between the initiations of different floral organs in Papilionoideae are shortened.     

FLORAL MORPHOLOGY,ORGANOGENESIS AND INTERPRETATION OF THE INFERIOR OVARY IN DOWNINGIA BACIGALUPII

The inflorescence of Downingia bacigalupii (Campanulaceae; Lobelioideae) is an indeterminate spike. Axillary flowers have a long, linear, inferior ovary with parietal placentation, a pentamerous synsepalous calyx, zygomorphic sympetalous corolla, syngenesious stamens, and a bicarpellate, syncarpous gynoecium. On the basis of floral vascular anatomy the inferior ovary is interpreted as appendicular, representing adnation of outer floral whorls to the gynoecium. Floral ontogeny shows that sepals are initiated in an adaxial to abaxial sequence rather than the 2/5 phyllotaxis reported for other members of Lobelioideae. Growth of the common bases of sepal lobes forms a floral cup and initiation of the following floral whorls occurs along the inner margins of the cup. Continued basal growth of the cup-shaped bud results in the formation of the elongated inferior ovary. Earlier evidence for the interpretation of a cup-shaped receptacle during development of epigynous flowers is reexamined and it is concluded that the concave floral bud of D. bacigalupii can also be interpreted as common growth of connate floral whorls, supporting interpretations based on vascular anatomy. Comparison of floral development between Downingia bacigalupii and Pereskia aculeata (Cactaceae) reveals ontogenetic differences between flowers with appendicular and receptacular cups.     

The Hormonal Regulation of Flower Development

Homeotic genes comprising the ABCE classes partly detail the genetic networks that control aspects of floral organ initiation, development, and architecture, but less is known about how these gene functions are translated into changes at the cellular level in growth and cellular differentiation that are involved in the formation of diverse floral organs with specific shapes and sizes. Hormones are the principal transducers of genetic information, and due to recent advances in understanding hormone function in floral development, it is timely to review some of these findings. Flower development is the result of a regulated balance between meristem size and coordination and organ initiation. Floral meristem size is regulated by cytokinin, gibberellin, and auxin, and auxin plays a major role in organ initiation and organogenesis. How hormones contribute to the development of each organ is partly known, with stamen development reliant on almost all hormones, petal development is affected by gibberellins, auxin, and jasmonic acid, and gynoecium development is predominantly regulated by auxin. Furthermore, the interconnections between genetic hierarchies and hormones are being elucidated, and as almost all hormone groups are implicated in floral development, points of hormone crosstalk are being revealed.     

HISTOGENESIS OF THE ANDROECIUM AND GYNOECIUM IN DOWNINGIA BACIGALUPII

A histogenetic investigation of the synandrous androecium and syncarpous gynoecium in the flower of Downingia bacigalupii Weiler (Campanulaceae; Lobelioideae) was undertaken for the purpose of comparing the modes of initiation, early growth and fusion in these floral whorls with that reported previously for the perianth in this species. Stamens are initiated as separate organs from the second tunica layer and underlying corpus regions of the concave floral meristem. Subsequent growth of stamens involves apical and intercalary growth in length and rudimentary marginal growth in breadth. Tissues of the four microsporangia originate from hypodermal sporangial initial cells and the filament is formed by intercalary growth at the base of the anther. Lateral fusion of stamens is ontogenetic and involves cuticular fusion of adjacent epidermal layers. The two emergent carpel primordia arise as crescentic organs by periclinal divisions in the second tunica layer and corpus zones. Carpel primordia also undergo apical and intercalary growth in length as well as extensive marginal growth in breadth. Radial growth in carpels is mediated by an adaxial meristem which shows its greatest concentration of activity at the carpel margins. Carpel fusion appears to be partially ontogenetic accompanied by zonal growth. Closure of the stylar canal is by the formation of a transmitting tissue derived from the protodermal layers of the adaxial carpel surfaces. A discoid nectary is initiated around the base of the style and formation of the inferior ovary is by intercalary growth of the base of the concave floral bud. The two parietal placentae originate as longitudinal outgrowths from the walls of the floral cup. Ovule initiation is simultaneous at first and then intercalary during subsequent elongation of the ovary. The ovules are anatropous, unitegmic and tenuinucellate. Stamen and carpel procambium shows a slight delay in differentiation when compared to that reported for the perianth and bract, but in all other respects carpels resemble other floral organs in their patterns of histogenesis and early growth. Stamens diverge from the other floral organs in their early pattern of growth, but a consideration of all features of their histogenesis suggests an appendicular rather than an axial interpretation of these organs.     

Patterns and Significance of Floral Development in Whytockia (Gesneriaceae)

Abstract: The floral development of Whytockia W. W. Smith has been studied in order to explore the developmental basis for the arrangement and differentiation patterns of floral organs, and the evolutionary relationship between Whytockia and allies in floral development. The descending imbricate aestivations in both calyx and corolla have remarkably different ontogenetic patterns between calyx and corolla which are derivative with respect to the development of the valvate aestivations in the four-stamened Rhynchoglossum. Both corolla lobes and stamens are initiated simultaneously from the same ring meristem. However, the five stamens remarkably precede the initiation of the five corolla lobes. Also, the adaxial stamen is suppressed after initiation to become a staminode, concomitant with retardation of its adjacent organs during development. This situation, together with the non-acropetal order among whorls of floral organs in Whytockia, is possibly related to a late expression and a remarkably different expression pattern of cycloidea- like genes as compared to Antirrhinum. Furthermore, the axile placentation in the bilocular ovary of Whytockia is formed by an involute closure of carpels rather than derived from a secondary fusion of two intrusive parietal placentae.     

Evolutionary loss of sepals and/or petals in detarioid legume taxa Aphanocalyx, Brachystegia, and Monopetalanthus (Leguminosae: Caesalpinioideae)

Floral development using scanning electron microscopy is compared in several taxa of the Brachystegia subtribal group of caesalpinioid tribe Detariae. This group is characterized by missing sepals and/or petals. In Aphanocalyx djumaensis, Monopetalanthus durandii, and two Brachystegia species, one sepal is initiated in median abaxial position. In the first two, one or two additional sepal rudiments may initiate late. Brachystegia species have all five sepals, which remain scalelike. In Aphanocalyx and Monopetalanthus, one petal initiates adaxially and medianly (a position atypical for the first initiated petal in the family); additional petal rudiments may form in lateral sites. In Brachystegia, five petals are initiated unidirectionally on a meristem ring, but all are suppressed after initiation. In all taxa, ten stamens are initiated on a ring meristem: unidirectionally in Monopetalanthus, bidirectionally in Brachystegia, vs. in erratic order in Aphanocalyx. Carpel and petal initiation are concurrent. Different organ whorls overlap in time in Monopetalanthus and Brachystegia. In all, the floral apex characteristically is elongate radially and narrow tangentially after bracteole initiation. Two ontogenetic features, the meristem ring and the radially elongate post-bracteole floral apex, appear to be possible synapomorphies for the Brachystegia group.     

茄科马尿泡和天仙子的花器官发生

利用扫描电镜研究了茄科 (Solanaceae)天仙子族 (Hyoscyameae)中国特有属马尿泡属 (PrzewalskiaMaxim .)马尿泡 (PrzewalskiatanguticaMaxim .)和天仙子属 (HyoscyamusL .)天仙子 (HyoscyamusnigerL .)的花器官发生和发育 ,研究结果表明 :马尿泡和天仙子花器官的发生和发育具有以下 3个共同特征 :1)符合Hofmeister规律 ,即新器官的发生首先出现在花顶已经存在的器官之间 ;2 )花冠的发育模式符合茄科植物所具有的“后合瓣”(“latesympetaly”)现象 ,即花瓣单独发生但后来又通过它们基部分生组织的融合而连合起来 ;3)花被五基数且花器官原基发生顺序为向心发育。但是它们的花萼原基具有不同的发生方式。天仙子花萼裂片原基的发生方式为环状发生 ;马尿泡花萼裂片原基的发生方式为螺旋状发生 ,但 5个花萼裂片原基在都出现后就连成了一个环。马尿泡是介于天仙子属和山莨菪属之间的类群 ,它比天仙子属原始但较山莨菪属进化。     

Floral Organogenesis and Its Systematic Significance of the Genus Nandina(Berberidaceae)

The initiation of the floral organs of Nandina domestica Thunb. (Berberidaceae) is of the trimemus-whorled pattern. Stamens and petals grew out from the lateral bifurcation of the common stamen-petal primordia; but petals underwent retarded periods of growth in their early development. Carpel initiation belongs to the ascidiate type. Some aspects concerning the trimerous floral organs, the origin of petals, stamen insertion pattem and monocarpellary pistil were discussed. In addition the floral ontogenetic characters among three genera of the Berberidaceae, i.e., Caulophyllum, Podophyllum and Nanclina were compared. It is inferred that the trimerous-whoded arrangement and the diversity of carpel initiation were the two unique characters of Nandina.     

Floral ontogeny in Dialiinae (Caesalpinioideae: Cassieae), a study in organ loss and instability

The Caesalpinioideae are widely variable in their floral ontogeny, and among caesalpinioids, members of the polyphyletic tribe Cassieae are particularly diverse. Within the Cassieae, the monophyletic Dialiinae clade is also marked by a high degree of organ loss, particularly in the largest genus, Dialium. The purpose of this work is to explore the ontogeny of several previously undocumented species of the diverse Dialiinae clade, with the goal of building a more complete picture of floral development and evolution in this group and especially within Dialium. We have documented the floral ontogeny of six species of the Dialiinae; four from Dialium, as well as Poeppigia procera and Mendoravia dumaziana. Mode and timing of organ initiation were mostly consistent across the Dialium species studied. With the exception of Dialium dinklagei, which undergoes helical calyx initiation, all flowers initiated sepals bidirectionally. In the instances of both gains and losses of floral organs in Dialium, one trend is apparent — an absence of abaxial organs. Gains in both sepals and stamens occur in the adaxial median position, while stamens and petals which are lost are always the ventral-most organs. Organ initiation in Poeppigia and Mendoravia is unlike that seen in Dialium. Poeppigia shows a ventral to dorsal unidirectional sepal initiation, while both Poeppigia and Mendoravia display near-synchronous initiation of the corolla and staminal whorls. The taxa examined here exemplify the apparent lack of developmental canalisation seen in caesalpinioid legumes. This ontogenetic plasticity is reflective of the morphological diversity shown by flowers across the subfamily, representing what has been described as an “experimental” phase in legume floral evolution.     

Floral Organogenesis and Development of Two Taxa in Tribe Hyoscyameae (Solanaceae)?aPrzewalskia tangutica and Hyoscyamus niger

Floral organogenesis and development of Przewalskia tangutica Maxim.endemic to China and Hyoscyamus niger L., which belong to the tribe Hyoscyameae (Solanaceae), were studied using scanning electron microscope. They have three common characters of floral organ initiation and development: 1) initiation of the floral organs in the two species follows Hofmeister’s rule; 2) the mode of corolla tube development belongs to the “late sympetaly” type; 3) primordia of the floral appendages initiated in a pentamerous pattern and acropetal order. But initiation of the calyx lobe primordia showed different modes in these two species. The calyx lobe primordia of H. niger have simultaneously whorled initiation, while those of P. tangutica have helical initiation, but the five calyx lobe primordia form a ring after all five calyx lobe primordia occur. The systematic significance of the present results in the genera Hyoscyamus and Przewalskia is discussed in this paper.     

Floral ontogeny of Cneorum tricoccon L. (Rutaceae)

The floral ontogeny of the Spurge olive (Cneorum tricoccon L.) is studied by means of scanning electron microscopic observations. Special attention is paid to the sequence of initiation of the floral parts, the occurrence of septal cavities, and the development of the nectariferous tissue. The nectary disc arises as a receptacular outgrowth below the ovary and independently from stamen development. By the extensive growth of this voluminous androgynophore, stamen filaments become enclosed by nectary tissue and as a result, they are seated in pits between the lobes of the disc. Between ovary and style, three lobes are present, which are covered with stomata – their function is unknown. The significance of the unusual trimery of the flower is discussed. Floral developmental evidence supports a Rutalean affinity, although more ontogenetic investigations are needed in Rutaceae, subfamily Spathelioideae.     

Floral ontogeny in <Emphasis Type="Italic">Astragalus compactus</Emphasis> (Leguminosae: Papilionoideae: Galegeae): variable occurrence of bracteoles and variable patterns of sepal initiation

Comparative studies of floral ontogeny represent a growing field that promise to provide new insights on floral evolution. Floral ontogenetic information has been used successfully in Leguminosae for re-examining phylogenetic relationships at different levels. Using epi-illumination light microscopy, we present original ontogenetic data in Astragalus compactus, which was chosen because of its unusual arrangement of inflorescence and variable occurrence of bracteoles on flowers. Based on our results, uncommon ontogeny of the inflorescence led to the arrangement of flowers in four different positions. Variation was observed not only in the presence of bracteoles, but also in the order of sepal initiation in flowers of the same inflorescence. Surprisingly, besides the widely stated unidirectional pattern, bidirectional, sequential and an atypical unreported order were observed. High degree of overlapping between whorls and formation of two types of common primordia also were found. The variable occurrence of bracteoles suggests that the species is in an intermediate state towards fully lacking of bracteoles. We propose that the variability of the sequence of sepal initiation is possibly a consequence of the function of mechanical forces generated by surrounding leaves. Relationships between mechanical force and auxin signalling are discussed.     

Floral and inflorescence morphology and ontogeny in Beta vulgaris, with special emphasis on the ovary position

Background and Aims

In spite of recent phylogenetic analyses for the Chenopodiaceae–Amaranthaceae complex, some morphological characters are not unambiguously interpreted, which raises homology questions. Therefore, ontogenetic investigations, emphasizing on ‘bracteoles’ in Atripliceae and flowers in Chenopodioideae, were conducted. This first paper presents original ontogenetic observations in Beta vulgaris, which was chosen as a reference species for further comparative investigation because of its unclarified phylogenetic position and its flowers with a (semi-)inferior ovary, whereas all other Chenopodiaceae–Amaranthaceae have hypogynous flowers.

Methods

Inflorescences and flowers were examined using scanning electron microscopy and light microscopy.

Key Results

Floral development starts from an inflorescence unit primordium subtended by a lateral bract. This primordium develops into a determinate axis on which two opposite lateral flowers originate, each subtended by a bracteole. On a flower primordium, first five tepal primordia appear, followed by five opposite stamen primordia. Simultaneously, a convex floral apex appears, which differentiates into an annular ovary primordium with three stigma primordia, surrounding a central, single ovule. A floral tube, which raises the outer floral whorls, envelops the ovary, resulting in a semi-inferior ovary at mature stage. Similarly, a stamen tube is formed, raising the insertion points of the stamens, and forming a staminal ring, which does not contain stomata. During floral development, the calyces of the terminal flower and of one of the lateral flowers often fuse, forming a compound fruit structure.

Conclusions

In Beta vulgaris, the inflorescence is compound, consisting of an indeterminate main axis with many elementary dichasia as inflorescence units, of which the terminal flower and one lateral flower fuse at a later stage. Floral parts develop starting from the outer whorl towards the gynoecium. Because of the formation of an epigynous hypanthium, the ovary becomes semi-inferior in the course of floral development.Key words: Beta vulgaris, Chenopodiaceae, floral ontogeny, gynoecial development, epigynous hypanthium, semi-inferior ovary, inflorescence ontogeny, LM, SEM     

Comparative inflorescence and floral ontogeny in the genus Mentha (Mentheae: Nepetoideae: Lamiaceae): variable sequences of organ appearance and random petal aestivation

The genus Mentha is a taxonomically complex genus, characterized by large morphological variations. Only a few, frequently overlapping, characters are of value in taxonomy. Comparative floral developmental studies provide an opportunity for better understanding the systematic relationships among different species. The inflorescence and floral ontogeny of three Mentha L. species (M. piperita L., M. pulegium L. and M. suaveolens Ehrh.) were investigated using epi-illumination light microscopy. All three species studied have thyrses with the same developmental pathway. The lack of higher order bracts and the monochasial branching of the higher order inflorescence apices were found as special features of inflorescence ontogeny. Sepals appear unidirectionally from the adaxial side in all except for M. pulegium which shows a modified unidirectional sequence. Variable sequences of petal and stamen appearance from unidirectional to reversed unidirectional sequence are present in all. Significant ontogenetic features include (1) appearance of the corolla as a rim before petal lobes become visible and (2) instability in petal aestivation. Morphological features including densely hairy calyx, five-lobed corolla tube, smaller adaxial stamens and hairy ovary with included style distinguish M. pulegium from the other species. On the basis of our results floral ontogenetic features could be considered important characters for delimiting or diagnosing different sections in the genus Mentha. Variable sequences of petal lobe appearance and instability in petal aestivation were found as unusual developmental characters.     

Trends in evolution of floral ontogeny in Cassia sensu stricto,Senna, and Chamaecrista (Leguminosae: Caesalpinioideae: Cassieae: Cassiinae); a study in convergence

Distinctions in floral ontogeny among three segregate genera (Cassia sensu stricto, Chamaecrista, and Senna) of Cassia L. support their separation. In all species studied, the order of floral organ initiation is: sepals, petals, antesepalous stamens plus carpel, and lastly antepetalous stamens. Sepal initiation is helical in all three genera, which however differ in whether the first sepal is initiated in median abaxial position (Senna), or abaxial and off-median (Cassia javanica), a rare character state among legumes. Order of petal initiation varies: helical in Senna vs. unidirectional in Cassia and Chamaecrista. Both stamen whorls are uniformly unidirectional. Intergeneric ontogenetic differences occur in phyllotaxy, inflorescence architecture, bracteole formation, overlap of initiation among organ whorls (calyx/corolla in Cassia; two stamen whorls in Chamaecrista), eccentric initiation on one side of a flower, anther attachment, anther pore structure, and precocious carpel initiation in Senna. The asymmetric corolla and androecium in Chamaecrista arise by precocious organ initiation on one side (left or right). The poricidal anther character can result from differing developmental pathways: lateral slits vs. sealing of lateral sutures; clasping hairs vs. sutural ridges; terminal pores (one or two) vs. none; and clamp layer formation internally that prevents lateral dehiscence. Genera differ in corolla aestivation patterns and in stigma type. Convergence is shown among the three genera, based on intergeneric dissimilarities in early floral ontogeny (floral position in the inflorescence, bracteole presence, position of the first sepal initiated, order of petal initiation, asymmetric initiation, overlap between whorls, anther morphology, and time of carpel initiation) resulting in similarities at anthesis (showy, mostly yellow salverform flowers, heteromorphic stamens, poricidal anther dehiscence, bee pollination, and chambered stigma).     

Morpho-histogenic studies on tendrils of Passiflora

The ontogenetic development of the tendril and its associatedorgans is investigated in 17 species of Passiflora. The shootapex shows a single tunica layer though the second layer simulatestunica. The cytohistological zonation is not a constant feature.In P. caerulea Linn., it is distinct at leaf initiation butin P. pruinosa Mast., P. vespertilio Linn., and P. watsonianaMast., it is indistinct. The main axillary bud differentiatesfrom the peripheral meristem of the shoot apex. The differentiationof this bud into floral and tendril menstems occurs at a nodeimmediately below the shoot apex in P. minima Blanco. and Pracemosa Brot. In other species this differentiation generallyoccurs at the lower nodes. The floral meristem is initiatedas an accessory bud from this bud, thus forming a bud complex.The residuum of the bud complex develops as a tendril. The thirdaccessory bud which does not originate from this bud complex,develops into a vegetative branch. The fundamental nature ofthe vascular relationship between the flower, tendril, accessorybud, subtending leaf, and the axis is similar in most of theinvestigated species.     

Blossom–end Rot of Pears: Systemic Infection of Flowers and Immature Fruit by Botrytis cinerea1

A histological study was made of the systemic growth of Botrytis cinerea from styles, stamens and sepals to the flower receptacle and mesocarp of immature pear fruit. In most styles, hyphal growth ceased in the upper portion at the onset of stylar senescence, which occurred at about 1 wk after full bloom. Hyphae never passed through styles into the carpel. Unlike the styles, hyphae in filaments grew without restriction and progressed within 4 days, via vascular tissue, through sepals into tissues of the upper end of the flower receptacle, or of the mesocarp adjoining the sepals, without causing symptoms. Filaments remained green to partly green until harvest. B. cinerea entered filaments and spread into the receptacle or mesocarp at any time between blossoming and harvest and then became latent in these tissues. Filaments were, however, more susceptible at the flowering stage. After 2 months floral tubes were closed, and the stamens protected from infection. Careful inspection of ripe, cold–stored fruit showed that decay invariably spreads from mesocarp tissue adjoining the sepals, outward along the vascular bundles, but not from secondary inoculum in the floral tube. The behaviour of the pathogen suggests that control of blossom–end rot could be achieved if pears are sprayed with fungicide at 75—100% petal fall (when most stamens are exposed) and a month later (before floral tubes started to close).     

Pseudodiplostemony, and its implications for the evolution of the androecium in the Caryophyllaceae

The androecium of the Caryophyllaceae is varied, ranging from a two-whorled condition to a single stamen. A number of species belonging to the three subfamilies, Caryophyl-loideae, Alsinoideae and Paronychioideae have been studied ontogenetically with the SEM to understand their peculiar androecial development in the broader context of the Caryophyllales alliance. Although patterns of initiation are highly variable among species, there are three ontogenetic modes of stamen initiation: all stamens simultaneous within a whorl, the antepetalous stamens simultaneous and the antesepalous sequentially with a reversed direction, or both whorls sequentially with or without a reversed direction. The most common floral (ontogenetic) sequence of the Caryophyllaceae runs as follows: five sepals (in a 2/5 sequence), the stamens in front of the three inner sepals successively, stamens opposite the two outermost sepals, five antepetalous stamens (simultaneously or in a reversed spiral superimposed on the spiral of the antesepalous stamens), five outer sterile (petaloid) organs arising before, simultaneously or after the antesepalous stamens, often by the division of common primordia. A comparison with the floral configurations of the Phytolaccaceae and Molluginaceae indicates that the outer petaline whorl of the Caryophyllaceae corresponds positionally to the alternisepalous stamens of somePhytolacca, such asP. dodecandra. The difference withP. dodecandra lies in the fact that an extra inner or outer whorl is formed in the Caryophyl-laceae, in alternation with the sepals. A comparable arrangement exists in the Molluginaceae, though the initiation of stamens is centrifugal. A comparison of floral ontogenies and the presence of reduction series in the Caryophyllaceae support the idea that the pentamerous arrangement is derived from a trimerous prototype. Petals correspond to sterillized stamens and are comparable to two stamen pairs opposite the outer sepals and a single stamen alternating with the third and fifth sepals. Petals are often in a state of reduction; they may be confused with staminodes and they often arise from common stamenpetal primordia. The antesepalous stamen whorl represents an amalgamation of two whorls: initiation is reversed with the stamens opposite the fourth and fifth formed sepals arising before the other, while the stamens opposite the first and second formed sepals are frequently reduced or lost. Reductive trends are correlated with the mode of initiation of the androecium, as well as changes in the number of carpels, and affect the antesepalous and antepetalous whorls in different proportions. It is concluded that the androecium of the Caryophyllaceae is pseudodiplos-temonous and is not comparable to diplostemonous forms in the Dilleniidae and Rosidae. The basic floral formula of Caryophyllaceae is as follows: sepals 5—petals 5 (sterile stamens)—antesepalous stamens 3+2—antepetalous stamens 5 gynoecium 5.     

吉祥草的花部器官发生及其系统学意义

利用扫描电镜（SEM）观察了吉祥草（Reineckia carnea）（铃兰科）的花部器官发生发育过程。吉祥草花被片、雄蕊的发生方式是由近轴端向远轴端发生的逆单向型（reversed unidirection）,花发育后期花被片合生形成花被筒,花丝与之贴生。伴随花被片、雄蕊发生,三枚心皮也由近轴向远轴方向相继发生,随后彼此合生发育。花序顶部的花易发生花器官数目变异。结合早期花原基形态以及花器官数目变异情况分析,吉祥草的花被片与雄蕊可能是由共同原基分化而成。从花部器官发生式样和花被筒形成时间两方面比较吉祥草属、白穗花属和铃兰属的特征发现,三属中,铃兰属处于相对进化的位置,而白穗花属比吉祥草属更为原始。