Comparative ontogeny of perfect and pistillate florets in Senecio vernalis (Asteraceae)

We studied the inflorescence, and in particular ontogeny and development of the florets in Senecio vernalis as a representative member of Asteraceae, using epi-illumination microscopy. Initiation and subsequent development of florets on the highly convex inflorescence apex occur acropetally, except for pistillate ray florets, which show a lag in initiation. Receptacular bracts derive from the receptacular surface after development of all florets. The order of whorl initiation in both disc and ray florets include corolla, androecium and finally the pappus, together with the gynoecium. Development of corolla lobes from a ring meristem occurs in bidirectional order starting from the lateral side, whereas stamens incept unidirectionally from the abaxial side. Concurrently with the inception of two median carpel primordia, a ring meristem develops at the base of the corolla from which pappus bristles differentiate in later stages. Pistillate ray florets show significant differences from perfect disc florets as reflected by the zygomorphic shape of the floral apex and a shift of floral merosity from pentamery to tetramery. Loss of stamens in ray florets occurs due to abortion of primordia after initiation.     

Comparative floral development in the tribe Mentheae (Nepetoideae: Lamiaceae) and its bearing on the evolution of floral patterns in asterids

A comparative developmental study of flowers was carried out using epi-illumination light microscopy on four genera of Lamiaceae (Nepeta, Rosmarinus, Salvia, andZiziphora), representing all three subtribes of Mentheae. All species examined share unidirectional (adaxial to abaxial) sepal initiation, except Rosmarinus, which has the reverse unidirectional sequence, starting abaxially. Initiated but suppressed bracteoles were detected only in Rosmarinus. In Rosmarinus, Salvia, and Ziziphora, initiation of petals and stamens proceeds unidirectionally from the abaxial side. Floral initiation of Nepeta has bidirectional inception of petals and unidirectional stamen initiation from the adaxial side. Temporal overlap in organ initiation between petal and stamen whorls occurs in all taxa, though this feature is more prominent in Rosmarinus. Significant structural and developmental features that distinguish the four genera include: (1) polysymmetric calyx tube, highly tomentose corolla and deeply four-partitioned ovary in Nepeta; (2) monosymmetric two-lipped calyx and shallowly four-partitioned ovary in Ziziphora; and (3) suppression of adaxial stamens in Salvia and Rosmarinus. Adaxial stamens are absent from Rosmarinus, but reduced stamens remain as staminodia in Salvia. In a phylogenetic context, the late monosymmetry of Nepeta and very early monosymmetry of Rosmarinus could both be regarded as derived conditions compared with the early monosymmetry ofSalvia and Ziziphora.     

Floral development in Scutellaria pinnatifida (Lamiaceae): the ontogenetic basis for sepal reduction

The Scutellaria is a Labiatae genus (subfamily Scutellarioideae) with a highly specialised floral structure. The genus is characterised by a peculiar two‐lobed calyx with a projecting appendage, named the scutellum. Here, we present a detailed analysis of floral development, using epi‐illumination light microscopy, to clarify open questions about its floral organisation. Floral whorls appeared in an acropetal sequence, with a marked temporal overlap of petal and stamen appearance. Organ appearance in each whorl proceeded unidirectionally from the abaxial to the adaxial side. Significant developmental features included the formation of the scutellum, reduction of sepal lobes and formation of a three‐lobed nectary disc. Our study revealed that both loss of organ initiation and fusion of primordia are responsible for the reduction in sepal members in Scutellaria. The nectary structure was markedly different from most other studied Lamiaceae.     

Pollen studies in the genus Echinops L. and Xeranthemum group (Asteraceae)

The phylogeny of the genus Echinops and the Xeranthemum complex were the subject of a previous molecular study of the tribe Cardueae. An electronic microscope survey of pollen morphology and ultrastructure is presented for all the genera belonging to these groups, allowing four pollen types to be identified. The exine pattern indicates that there are two pollen types in the genus Echinops (including Acantholepis ), although no differences have been found between sections in Echinops . First, the annual species of Echinops and Acantholepis orientalis show a pollen type that differs from that of perennial species of the former genus and, second, the genera Chardinia and Xeranthemum exhibit a pollen type distinct from that Amphoricarpos and Siebera . The internal structure of the pollen wall is the same for all the genera. Only slight differences were observed in the tectum, but in all cases these were of the anthemoid type. Statistically significant correlations between pollen size and the life cycle were found.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 549–557.     

Floral display and pollination success in Senecio jacobaea (Asteraceae): Interactive effects of head and corymb size

The self-sterile Senecio jacobaea (Asteraceae) presents its rayed heads in large, compound inflorescences (corymbs). I examined the role of head and corymb size in pollinator attraction, and whether the positive effect of intact rays (if any) depends on the size of the corymb. Using female fertility as a measure of pollination success, I assessed the performance of stems representing four experimentally produced character combinations: (1) few heads without rays, (2) many heads without rays, (3) few heads with rays, and (4) many heads with rays. The proportion of flowers setting fruit was higher for intact stems (treatments 2, 4) than for stems on which the majority of the heads had been removed (treatments 1, 3), suggesting selection for maximum inflorescence production. By contrast, experimental removal of all rays had a relatively weak negative effect on fruit set, with few-headed stems (treatment 1) experiencing a greater reduction than stems with many heads (treatment 2). These results suggest that clusters of heads produce a synergistic effect on pollinator attraction, allowing plants to maintain high visitation rates even if there are drastic reductions in the basic attraction units. Hence, the number of heads and the attractiveness of the individual heads interacted in their effect on pollination success. Fruit set per flower differed greatly between sites and was positively correlated with plant density.     

Effects of variation in flower number on pollinator visits in Cirsium purpuratum (Asteraceae)

We examined the functional relationships between floral display and two types of bumble bee response, the visitation rate per plant and the number of flowers visited on a plant, in an artificially arranged field population of Cirsium purpuratum. To reduce the variance in data, we collected data for each day separately and adopted a Latin square design in selecting the focal plants within a day. We then tested several types of regressions to each set of data to find the best-fitting line accounting for the observed relationship between pollinator response and display size. We found that the visitation rate of bumble bees per plant was a decelerating function of floral display, and that the number of flowering heads visited on a plant increased linearly with display size. Predicted from the above two functions, the visitation rate per head was independent of floral display and nearly constant within each day. Our results suggest that conventional methods in collecting and analyzing data on pollinator visitation may yield large variance in data derived from temporal and spatial heterogeneity and that improved methods employed here are effective in reducing the variance and estimating patterns of pollinator response to floral display more accurately.     

Cleistogamy inCentaurea melitensis (Asteraceae): Capitulum variability and spatio-temporal development patterns

Centaurea melitensis is a cleistogamous species of Mediterranean distribution, which normally produces a wide range of capitula varying in terms of morphology, size, position in the shoot system and other aspects. For that reason, and particularly in view of the pseudanthic nature of the flower head in Asteraceae, a preliminary study to characterise cleistogamy in this species was considered of interest. Capitular heteromorphism observed inC. melitensis was confirmed by principal component analysis (PCA). The five capitulum types differentiated [initial cleistogamous (iCL), intermediate cleistogamous (xCL), final cleistogamous (fCL), pseudocleistogamous (PCL) and chasmogamous (CH)] fit development patterns specific for both placement on the plant and timing. The balance between cleistogamy and chasmogamy is correlated with the final height of the plant. All these features are consistent with those reported for other cleistogamous species.     

阔叶杨桐的花器官发生(山茶科)

利用扫描电镜首次观察了山茶科厚皮香亚科植物阔叶杨桐的花器官发生过程。阔叶杨桐的花被片和五束雄蕊都是2/5螺旋向心发生,且有逆时针和顺时针两种螺旋方式;五束雄蕊在环形雄蕊原基上产生,且每一束都是由中间向两端发生;由五心皮形成的中轴胎座内出现一衍生的可育胎座。阔叶杨桐的花器官发生过程与本亚科的猪血木明显不同,该研究为厚皮香亚科乃至山茶科的系统发育与演化提供花器官方面的依据。     

滇鼠刺花的形态发生(鼠刺科)

在扫描电镜下,观察了滇鼠刺(Itea yunnanensis Franch.)花的形态发生.花3朵一束,排成总状花序.花器官为轮状结构,向心发生;花萼以2/5螺旋式相继发生,5个花瓣原基几乎同步地在花萼内侧与其互生的位置发生.雄蕊单轮对萼.当雄蕊发生后,花顶中心的分生组织开始凹陷,成为浅锅状;在其周围出现一个环状的分生组织,随之,2心皮原基产生,进而发育为马蹄形.初期的心皮相互分离,随着进一步发育,心皮内卷,彼此靠近、紧贴,逐渐于腹面合生,形成2室的中轴胎座;花柱的腹维管束通过薄壁组织连通;花期柱头融合,因此该种为合生心皮.对鼠刺属(Itea)及相关类群花发育性状和花结构进行了比较,支持把鼠刺属提升为鼠刺科(Iteaceae)的观点.     

Floral development and vasculature in Eriocaulon (Eriocaulaceae) provide insights into the evolution of Poales

Background and AimsFloral developmental studies are crucial for understanding the evolution of floral structures and sexual systems in angiosperms. Within the monocot order Poales, both subfamilies of Eriocaulaceae have unisexual flowers bearing unusual nectaries. Few previous studies have investigated floral development in subfamily Eriocauloideae, which includes the large, diverse and widespread genus Eriocaulon. To understand floral variation and the evolution of the androecium, gynoecium and floral nectaries of Eriocaulaceae, we analysed floral development and vasculature in Eriocaulon and compared it with that of subfamily Paepalanthoideae and the related family Xyridaceae in a phylogenetic context.MethodsThirteen species of Eriocaulon were studied. Developmental analysis was carried out using scanning electron microscopy, and vasculature analysis was carried out using light microscopy. Fresh material was also analysed using scanning electron microscopy with a cryo function. Character evolution was reconstructed over well-resolved phylogenies.Key ResultsPerianth reductions can occur due to delayed development that can also result in loss of the vascular bundles of the median sepals. Nectariferous petal glands cease development and remain vestigial in some species. In staminate flowers, the inner stamens can emerge before the outer ones, and carpels are transformed into nectariferous carpellodes. In pistillate flowers, stamens are reduced to staminodes and the gynoecium has dorsal stigmas.ConclusionsFloral morphology is highly diverse in Eriocaulon, as a result of fusion, reduction or loss of perianth parts. The nectariferous carpellodes of staminate flowers originated first in the ancestor of Eriocaulaceae; petal glands and nectariferous branches of pistillate flowers originated independently in Eriocaulaceae through transfer of function. We present a hypothesis of floral evolution for the family, illustrating a shift from bisexuality to unisexuality and the evolution of nectaries in a complex monocot family, which can contribute to future studies on reproductive biology and floral evolution in other groups.     

Chemotaxonomic value of flavonoids in Chromolaena congesta (Asteraceae)

The phytochemical investigation on the aerial parts of Chromolaena congesta led to the isolation of nine flavonoids, known in the literature as genkwanin (1) kumatakenin (2) acacetin (3), kaempferol 3-methyl ether (4), apigenin (5), apigenin 5,7-dimethyl ether (6), apigenin 5-methyl ether (7), luteolin (8) and kaempferol (9). The chemical structures were established on the basis of spectral evidence. All the compounds were isolated from this species for the first time. The results from the present study provide further information about the flavonoids as taxonomic marker of the genus Chromolaena, and the chemotaxonomic significance of these compounds were also summarized.     

The resurrection of Erigeron parryi (Asteraceae)

Erigeron parryi was described in 1890 from a single collection from southwest Montana. No additional collections were made during the following 90 years. Recent floristic treatments have synonomized E. parryi under E. ochroleucus. I used principal components and discriminant analyses of morphological characters to examine the relationship of E. parryi to its presumed closest relatives, E. ochroleucus, E. radicatus, and E. scribneri, in light of several populations discovered in the past 20 years. Erigeron parryi should be considered a distinct species. It can be readily distinguished from closely related species based on indument and caudex morphology. It is allopatric with E. ochroleucus and E. scribneri and ecologically separated from E. radicatus. Erigeron scribneri is intermediate between E. ochroleucus and E. radicatus and is probably best treated as a variety of one or the other of these species.     

Early floral development of Camellioideae (Theaceae)

The early floral development of Camellioideae was studied. Two major evolutionary lineages were recognized for this subfamily. The earlier evolved lineage (Camellia, Polyspora, and Pyrenaria) has normally 11-14 perianth members, which are initiated in a continuous spiral and are differentiated into sepals and petals at late floral development, and numerous stamens initiated individually and centrifugally on the whole androecial region. The later derived lineage (Franklinia, Hartia, Schima, and Stewartia) has five sepals and five petals arranged in two whorls, and numerous individual stamens originating centrifugally from the five petal-opposed zones. Hartia-Stewartia and Franklinia-Schima further diverged as two branches - the former is characterized by having androecial fascicles and axile-basal placentation. The androecial fascicle is considered to be derived within this subfamily. The latter exhibits a higher degree of carpellary congenital fusion and axile-central placentaion, and as a whole, is concluded to be the most advanced group in the Camellioideae. A taxonomic treatment of the Camellioideae at the tribal level is also proposed.     

A taxonomic revision of Centaurea section Acrocentron (Asteraceae) in Iran

The taxonomic status of Centaurea section Acrocentron in Iran is briefly reviewed. A critical study of 251 herbarium specimens, and an additional 37 accessions collected specifically for this research, led to the discovery of a new variety, Centaurea irritans var. longispinosa Montazerolghaem , and the revival of another, C. persica var. subinermis, a taxon previously treated as a synonym for about 25 years. A key to all Iranian species of Centaurea section Acrocentron is provided. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 163 , 99–106.     

Molecular cytogenetics of Xeranthemum L. and related genera (Asteraceae, Cardueae)

Abstract: Seven representatives of the genera Amphoricarpus, Chardinia, Siebera, and Xeranthemum, all of them closely related as demonstraded by molecular phylogeny, have been studied from a cytogenetic perspective. Morphometrical karyotype parameters were calculated and idiograms obtained. Fluorochrome banding was performed with chromomycin A₃ to identify GC-rich regions in the chromosomes. Fluorescence in situ hybridization allowed us to locate the sites of 18S-5.8S-26S and 5S rDNA. Silver nitrate staining was used to count the number of nucleoli and to detect the active nucleolar organizing regions. Systematic and evolutionary issues are addressed in the light of these data.     

The internal cuticle of Cirsium horridulum (Asteraceae) leaves

Leaf internal cuticle has not previously been studied in detail, and yet its existence has profound implications for the path of water movement. The internal cuticle forms a uniform layer on the inner periclinal epidermal walls that border substomatal cavities. This cuticle is continuous with the external cuticle through the stomatal pores. The thickness of the internal cuticle on nonstomatal epidermal cells is approximately one-third that of the external cuticle on the same cells. On both the abaxial and adaxial sides of the leaf the internal cuticle forms irregularly shaped islands bordered by mesophyll cells. The size of the islands coincides with the epidermal area of the substomatal cavity. The internal cuticle remains intact and connected to the external cuticle after incubation in cellulytic enzymes. After treatment with sulfuric acid or chloroform, both cuticles remain intact. The autofluorescence of both cuticles is increased by staining with auramine O. These results indicate that large portions of the leaf epidermis are covered by both an internal and an external cuticle.     

Floral ontogeny in ficinia and isolepis (cyperaceae), with focus on the nature and origin of the gynophore

BACKGROUND AND AIMS: The generic delimitations of Ficinia and Isolepis, sister genera in the Cypereae, are blurred. Typical Ficinia flowers have a lobed gynophore, which envelops the base of the nutlet, whereas in Isolepis the character is considered to be absent. Some former species of Isolepis, lacking the gynophore, were recently included in Ficinia. The floral ontogeny of representative taxa in Ficinia and Isolepis were investigated with the aim of evaluating the origin and nature of the gynophore in the Cypereae. METHODS: The spikelet and floral ontogeny in inflorescences collected in the field was investigated using scanning electron microscopy (SEM) and light microscopy (LM). KEY RESULTS: SEM images of Isolepis setacea and I. antarctica, Ficinia brevifolia, F. minutiflora, F. zeyheri and F. gracilis, and LM sections of F. radiata, show that the gynoecium in Ficinia is elevated above the flower receptacle by the development of a hypogynous stalk. From its apex, a (often three-)lobed cup is formed, which envelopes the basal part of the later nutlet. In developing flowers of I. antarctica, a rudimentary hypogynous stalk appears. In I. setacea, rudiments of a hypogynous stalk can be observed at maturity. In F. radiata and F. zeyheri, intralocular hairs are present in the micropylar zone. At the surface of developing gynoecia in flowers of F. gracilis, star-shaped cuticular structures appear which disappear again at maturity. CONCLUSIONS: The overall floral ontogeny of all species studied occurs following a typical scirpoid pattern, though no perianth primordia are formed. The gynophore in Ficinia originates as a hypogynous stalk, from which the typical gynophore lobes develop. The gynophore is not homologous with the perianth.     

Ontogeny of pistillate flowers and inflorescences in Nothofagus subgenus Lophozonia (Nothofagaceae)

  Cupule and pistillate inflorescence morphology is described in detail for the first time for a number of species in Nothofagus subgenus Lophozonia. The architecture and temporal appearance of prophylls, flowers, and cupule valves is dichasial; the cupule valves are third and higher order shoot systems. Comparative studies demonstrate that the dorsal rows of appendages on the cupule valves have a similar arrangement, and each row exhibits the same temporal pattern of development. This suggests that the cupule valves in all species have a modular construction and consist of rows of homologous appendages. This study clearly demonstrates the uniform groundplan of the pistillate inflorescence in this subgenus. Received March 14, 2002; accepted May 8, 2002 Published online: September 13, 2002     

Development and characterization of nine new microsatellite markers in Taraxacum (Asteraceae)

This study aims at developing and characterizing new microsatellite primer pairs in Taraxacum officinale auct. to produce polymorphic markers for genetical and evolutionary studies on apomixis in this sexual‐apomictic complex. A total of 24 diploid plants were tested for allelic polymorphism and heterozygosity. Out of nine loci three deviated significantly from the Hardy–Weinberg equilibrium expectations, probably due to the presence of null‐alleles. Successful cross‐species amplification was obtained for all markers in 29 Taraxacum microspecies from five sections.