Breeding system of a plesiomorphic floral type: an investigation of small flowered Streptocarpus (Gesneriaceae) species

Six different floral morphologies can be found among the ca. 146 species of Streptocarpus occurring in Africa and Madagascar. One of these, a simple, small pouch type, was found to be plesiomorphic for the genus after mapping these floral types onto a molecular phylogeny. The breeding systems and population structure of three species possessing the plesiomorphic small floral morphology, S. micranthus, S. ibityensis and S. lanatus, have been investigated using nuclear microsatellite markers. Significant deviations from panmixia were found both at the between and within population level (S. micranthus θ = 0.708, f = 0.786; S. ibityensis, θ = 0.173, f = 0.138; S. lanatus, θ=0.539, f = 0.646). As a florally diverse genus, Streptocarpus is unusual in having a predominantly selfing, mixed mating breeding system as a plesiomorphic condition.     

Developmental analyses of the phyllomorph formation in the rosulate species Streptocarpus rexii (Gesneriaceae)

Although some species of Streptocarpus (Gesneriaceae) do not possess a layered shoot apical meristem (SAM), but three individual meristems, the basal meristem (BM), the petiolode meristem (PM) and the groove meristem (GM) on the petiolode from which additional phyllomorphs are formed. To gain insights into the processes involved, we examined the development of seedlings from germination to the formation of the primary phyllomorph in S. rexii, a rosulate species. Our specific focus was to examine the relationship between the functional activity of the GM and meristematic activity, which was assessed by a combined analysis of toluidine blue staining of histological sections and the incorporation of BrdU into meristematic tissues. The results were integrated into 3-D graphics, which suggests a complex spatial and temporal interaction within the GM. The significance of our observations is discussed and compared to the SAM observed in most other angiosperms.     

Inflorescence development of Whytockia (Epithemateae, Gesneriaceae) and phylogenetic implications within Gesneriaceae

 The inflorescence development in Whytockia has been studied in order to explore the developmental basis for inflorescence architecture. The developmental pattern of the pair-flowered cyme in Whytockia basically conforms to that of most members in Gesneriaceae. However, the additional flower beside the terminal one in Whytockia is not equivalent to the frontal flower as in other Gesneriaceae because the former is located in the front-lateral position while the latter is in the front-median position. Also, the zigzag monochasial branching system in Whytockia represents the consecutive front-lateral branches rather than the lateral branches as in other Gesneriaceae. The inflorescence in Whytockia is flowering in a basipetal sequence, and its seemingly acropetal flowering sequence is due to the vigorous development of the consecutive front-lateral branches. In addition, the inflorescence of Whytockia does not represent the basic unit of the inflorescence in Epithemateae, and it is derived as compared to that of Rhynchoglossum. The development relationships of the inflorescence between Whytockia and its allies in Epithemateae are discussed on the basis of developmental and comparative evidence. Received February 15, 2002; accepted September 17, 2002 Published online: December 11, 2002     

Studies on the early floral development inCleomoideae (Capparaceae) with emphasis on the androecial development

Floral ontogeny ofCleome spinosa, Cleome violacea andPolanisia dodecandra subsp.trachysperma was studied in the context of the question whether the fascicled androecium ofReseda andCapparis (with fused fascicles) or the 2 + 4-pattern of theBrassicaceae is primitive in theCapparales. InPolanisia dodecandra, the 9–18 stamens show unidirectional initiation from the adaxial side toward the abaxial side of the flower. InCleome violacea, the six stamens also are formed in an unidirectional order, but development starts abaxially and a zigzag-like pattern is superimposed. InCleome spinosa, two stamen primordia in transversal (lateral) position are followed by four stamens which arise on a somewhat higher level in two pairs in front of the median sepals. It is assumed that the evolutionary steps in the androecial development proceed fromReseda viaCapparis andPolanisia/Cleome toBrassicaceae. This interpretation is supported byrbcL-studies (Chase & al. 1993,Rodman & al. 1993).Dedicated to emer. Univ.-Prof. DrFriedrich Ehrendorfer on the occasion of his 70th birthday     

Inflorescence and floral development in Astragalus lagopoides Lam. (Leguminosae: Papilionoideae: Galegeae)

Inflorescence and floral organogenesis and development of the bushy perennial legume Astragalus lagopoides of the section Hymenostegis were studied by means of epi-illumination light microscopy. Based on our observations, the primordia of lanceolate racemose inflorescences are born in the axils of leaves. Each inflorescence apex initiates acropetally bracts and floral apices for some time and then eventually ceases meristematic activity and forms an oblong-shaped terminal structure. The formation of such atypical terminal protrusion on the inflorescence meristem is judged to be a diagnostic feature for well-organized cessation of meristem morphogenesis. Pentamerous perfect flowers of the plant show strong zygomorphy and marked overlap in time of initiation among different organ primordia. Unexpectedly, sepal initiation is bidirectional starting from the lateral sides of the floral apex. Other significant developmental feature includes the existence of two types of common primordia, which are formed successively. From the primary common primordia there are produced antesepalous stamens and secondary common primordia. In comparison, the five secondary common primordia subdivide into a petal and an antepetalous stamen primordia. Initiation of two different types of common primordia is possibly the result of rising overlap in time of initiation of organs and demonstrates an advanced developmental style in the genus Astragalus.     

Anisocotyly and meristem initiation in an unorthodox plant, <Emphasis Type="Italic">Streptocarpus rexii</Emphasis> (Gesneriaceae)

In common with most Old World Gesneriaceae; Streptocarpus Lindl. shows anisocotylous growth, i.e., the continuous growth of one cotyledon after germination. Linked to this phenomenon is an unorthodox behaviour of the shoot apical meristem (SAM) that determines the growth pattern of acaulescent species (subgenus Streptocarpus). In contrast caulescent species develop a conventional central post-embryonic SAM (mainly subgenus Streptocarpella). We used S. rexii Lindl. as a model to investigate anisocotyly and meristem initiation in Streptocarpus by using histological techniques and analyses of the expression pattern of the meristematic marker SrSTM1 during ontogeny. In contrast to Arabidopsis thaliana (L.) Heynh., S. rexii does not establish a SAM during embryogenesis, and the first evidence of a SAM-like structure occurs during post-embryonic development on the axis (the petiolode) between the two cotyledons. The expression pattern of SrSTM1 suggests a function in maintaining cell division activity in the cotyledons before becoming localized in the basal meristem, initially at the proximal ends of both cotyledons, later at the base of the continuously growing macrocotyledon, and the groove meristem on the petiolode. The latter is equivalent to a displaced SAM seemingly originating de novo under the influence of endogenous factors. Applied cytokinin retains SrSTM1expression in the small cotyledon, thus promoting isocotyly and re-establishment of a central post-embryonic SAM. Hormone-dependent delocalization of the process of meristem development could underlie anisocotyly and the unorthodox SAM formation in Streptocarpus. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

New chromosome counts inStreptocarpus (Gesneriaceae) from Madagascar and the Comoro Islands and their taxonomic significance

This study records the chromosome numbers of 10 species ofStreptocarpus; nine of the counts are new. With the exception ofS. buchananii of mainland Africa, all the results are for plants endemic to Madagascar and the Comoro Islands. While there is a strong correlation between basic number and growth form in the two subgenera of the genus on the African mainland (x = 15 among caulescent species in subgenusStreptocarpella; x = 16 among acaulescent species in subgenusStreptocarpus), the situation appears more complex among Madagascan and Comoro Island species. One notable example of deviation from this correlation is shown byS. papangae, a shrubby caulescent species, with 2n = 32 (x = 16). Polyploidy in the genus appears to be absent on mainland Africa, but is present in Madagascar and the Comoro Islands, ranging from tetraploidy to octoploidy. Evolutionary implications of the cytological observations are considered.     

Comparative floral anatomy of Strobilanthinae (Acanthaceae), with particular reference to internal partitioning of the flower

This paper provides the first comparative survey of structural variation in inflorescence architecture and flower structure of Hemigraphis and other members of the subtribe Strobilanthinae (Acanthaceae). Several discrete structural characters are identified which may provide support for phylogenetic relationships within the group. These include (1) the presence or absence of an accessory bud, (2) the presence or absence of a hollow style, (3) the presence or absence of an abscission layer, (4) the number of stamens comprising the androecium, and (5) the pattern of filament detachment. The structure of the filament curtain, a complex structure that partitions the flower, is also investigated. A more precise term for this structure stapetal curtain is suggested since it is a result of close synorganisation between the filaments and corolla tube. This structure appears to have a wide distribution throughout Acanthaceae and is not confined to Ruellieae s.l., as previously described. The earlier characterisation of four discrete types of filament curtain is unsatisfactory, since many of the features used to distinguish them are continuous and not unique features of particular species.We acknowledge Richard Bateman, Mark Carine, Peter Endress, Colin Hughes, Toby Pennington and an anonymous reviewer for comments on this paper. ECM gratefully acknowledges Chrissie Prychid, Peter Gasson, and the late Tim Lawrence of the Micromorphology section, Royal Botanic Gardens, Kew for their assistance and encouragement and Jesus Cordero-Salvado for help with the figures. This work was supported by the Druce Fund from the University of Oxford.     

Three new species of Gasteranthus (Gesneriaceae) from Ecuador

The gesneriad flora of the Reserva Río Guajalito, Province of Pichincha, and Bosque Protector Otonga, Province of Cotopaxi, Ecuador have been investigated. Three new species,Gasteranthus aurantiacus M. Freiberg,G. atrolimbus M. Freiberg, andG. acuticarinatus M. Freiberg, are described and illustrated in preparation for a contribution for the Gesneriaceae in the Flora of Ecuador. While bothG. acuticarinatus andG. atrolimbus are characterized by a dorsal keel on a tubular, pink to wine-red corolla, the infundibulate, bright orange-colored corolla ofG. aurantiacus has a rather wide opening and a large limb.     

Early inflorescence and floral development in Cocos nucifera L. (Arecaceae: Arecoideae)

Palms are generally characterized by a large structure with a massive crown that creates difficulties in anatomical studies. The flowering behaviour of palm species may be a useful indicator of phylogenetic relationships and therefore evolutionary events. This paper presents a detailed histological study of reproductive development in coconut (Cocos nucifera L.), from initiation up to maturation of staminate and pistillate flowers. Reproductive development in coconut consists of a sequence of individual events that span more than two years. Floral morphogenesis is the longest event, taking about one year, while sex determination is a rapid process that occurs within one month. The inflorescence consists of different ultimate floral structural components. Pistillate flowers are borne in floral triads that are flanked by two functional staminate flowers. The staminate flowers are born in floral diads towards the base of the rachilla followed by solitary flowers in the middle to top of the rachilla. Three primary phases were identified in reproductive development, namely, transition of axillary bud into inflorescence bud, formation of floral buds, and sexualisation of individual flower buds. All developmental events with respect to stage or time of occurrence were determined.     

Comparative floral anatomy and ontogeny in Magnoliaceae

Floral anatomy and ontogeny are described in six species of Magnoliaceae, representing the two subfamilies Liriodendroideae (Liriodendron chinese and L. tulipifera) and Magnolioideae, including species with terminal flowers (Magnolia championi, M. delavayi, M. grandiflora, M. paenetalauma) and axillary flowers (Michelia crassipes). The sequence of initiation of floral organs is from proximal to distal. The three distinct outermost organs are initiated in sequence, but ultimately form a single whorl; thus their ontogeny is consistent with a tepal interpretation. Tepals are initiated in whorls, and the stamens and carpels are spirally arranged, though the androecium shows some intermediacy between a spiral and whorled arrangement. Carpels are entirely free from each other both at primordial stages and maturity. Ventral closure of the style ranges from open in Magnolia species examined to partially closed in Michelia crassipes and completely closed in Liriodendron, resulting in a reduced stigma surface. Thick-walled cells and tannins are present in all species except Michelia crassipes. Oil cells are normally present. Floral structure is relatively homogeneous in this family, although Liriodendron differs from other Magnoliaceae in that the carpels are entirely closed at maturity, resulting in a relatively small stigma, in contrast to the elongate stigma of most species of Magnolia. The flower of Magnolia does not terminate in an organ or organ whorl but achieves determinacy by gradual diminution.     

Aspects of floral structure and phenology in the genusConophytum (Mesembryanthemaceae)

The complex floral structure in the southern African genusConophytum (Mesembryanthemaceae; 77 spp.) is described in detail and assigned to three basic floral types, two of which can be divided into two subtypes. Correlations between structural features and phenological patterns are demonstrated and discussed in the family context as well as in relation to the systematic subdivision of the genus.     

Inflorescence and floral ontogeny in Crocus sativus L. (Iridaceae)

Inflorescence and floral ontogeny of the perennial, herbaceous crop Crocus sativus L. were studied using epi-illumination light microscopy. After production of leaves with helical arrangement a determinate inflorescence forms which becomes completely transformed into a single terminal flower. In some cases, bifurcation of the inflorescence meristem yields two or three floral meristems. The order of floral organs initiation is outer tepals – stamens – inner tepals – carpels. Stamens and outer tepals are produced from the lateral bifurcation of three common stamen-tepal primordia. Within each whorl, organs start developing unidirectionally from the adaxial side, except for the stamens which begin to grow from the abaxial side. Specialized features during organ development include interprimordial growth between tepals forming a perianth tube, fusion at the base of stamen filaments, and formation of an inferior ovary with unfused styles.     

Structure and development of the ovule and seed in Aristolochiaceae, with particular reference to Saruma

All members of Aristolochiaceae have anatropous, bitegmic, crassinucellate ovules, which are endostomic except in Saruma and Asarum arifolium where ovules are amphistomic. The outer integument is two cell-layered and the inner integument is three cell-layered. The chalazal megaspore is the functional one. All these conditions appear to be plesiomorphic for the order Piperales, which consists of five families, Aristolochiaceae, Hydnoraceae, Lactoridaceae, Piperaceae and Saururaceae. The embryo sac in Aristolochiaceae is eight-nucleate and corresponds to the Polygonum type; a hypostase is frequently present in this family. The seed coat of Aristolochia s.l., Asarum, Saruma and some Thottea species consists primarily of a two cell-layered testa, and a three cell-layered tegmen. In some species the cells of the outer epidermis become radially elongated, forming reticulate wall thickenings. Cells of the inner layer of the testa have crystals and thickened inner walls. The three layers of the tegmen are tangentially elongated, and become cross fibres at maturity, as fibres of the outer and inner layers are parallel to the seed axis, whereas those of the middle layer are perpendicular to it. This type of seed coat anatomy is synapomorphic for Aristolochiaceae. In addition, the gross morphology of the seed and elaiosome histology are remarkably similar in Asarum and Saruma, thus supporting a sister-group relationship between them. Embryological and seed characters do not supply any synapomorphy that support a close relationship between Aristolochiaceae, Hydnoraceae and Lactoridaceae. Instead, some seed features such as the absence of seed appendages and the collapsed cells of endotesta may indicate a close relationship of Lactoris with Piperaceae plus Saururaceae, although this is the subject of further analysis.     

A new species of Sinningia (Gesneriaceae) from northeastern Brazil

Sinningia nordestina is described and illustrated. Morphological and molecular characters are discussed. It is a new species endemic to northeastern Brazil and is distinguished from other members of the genus by its vestigial tubers, ascending pedicels with pendent flowers, small corollas, and deviating flowering period.     

A Floral Ontogenetic Approach to Questions of Homology within the Cyperoideae (Cyperaceae)

Within the Cyperoideae, which comprise all Cyperaceae except the Mapanioideae, several questions of homology are discussed and reinterpreted based on results of our SEM and LM floral ontogenetic studies. In all species studied, spikelets are interpreted as being indeterminate, with spirally to distichously arranged glumes, each subtending (or not) a flower. Floral development starts with the formation of two lateral stamen primordia, simultaneously with, or followed by the formation of a third, abaxial stamen primordium. Perianth parts, if present, originate only after the formation of the androecium, simultaneously with the appearance of an annular ovary primordium, surrounding a central ovule primordium. Perianth parts vary in number and morphology, and, where present, perianth development follows a general pattern. Three (or two) stigma primordia are formed on the top of the rising ovary wall. In dimerous gynoecia, stigma primordia originate either dorsiventrally, resulting in a laterally flattened ovary/nutlet, or laterally, resulting in a dorsiventrally flattened ovary/nutlet. We conclude that in all species studied the spikelet and floral development occurs according to a general, scirpoid, ontogenetic pattern, which we illustrate using new spikelet and floral ontogenetic results in Eleocharis palustris and other species. Spikelet and floral ontogeny in species with apparently deviating morphologies, can be traced back to the general ontogenetic pattern.

---

Resumen  Varias preguntas sobre homología para las Cyperoideae, que incluyen todas las Cyperaceae excepto las Mapanioideae, se discuten e interpretan con base en estudios de ontogenia floral realizados con SEM y LM. En todas las especies estudiadas, las espiguillas son indeterminadas con glumas arregladas en espiral o dicotomicamente, cada una sosteniendo (o no) una flor. El desarrollo floral comienza con la formación de dos primordios estaminales laterales, simultáneamente con o seguido por la formación del tercer primordio estaminal abaxial. Si se desarrollan las partes del perianto, se originan solo después de la formación del androceo, simultáneamente con el desarrollo del primordio anular del ovario que envuelve al primordio central del óvulo. Cuando están presentes las partes del perianto, varían en número y morfología y el desarrollo sigue un patrón general. Se forman tres (o dos) primordios del estigma en el ápice de la pared del ovario en desarrollo. En gineceos dímeros, los primordios de los estigmas se originan dorsiventralmente resultando en una nuececilla/ovario comprimido lateralmente, o se originan lateralmente, resultando en una nuececilla/ovario comprimido dorsiventralmente. Concluimos que, tanto el desarrollo floral, como el de las espiguillas en todas las especies estudiadas, siguen un patrón ontogenético general scirpoide que se ilustra con los resultados obtenidos para Eleocharis palustris y otros especies. La ontogenia floral y de las espiguillas en especies con morfologías aparentemente atípicas, puede estar reducida al patrón ontogenetico general.

     

Single nucleotide polymorphisms of Gcyc1 (Cycloidea) in Conandron ramondioides (Gesneriaceae) from Southeast China

Conandron ramondioides with actinomorphic flower in Gesneriaceae is an endemic species distributed in Taiwan, Southeast of China and Japan. Populations are usually small and isolated in typically fragmented habitat. Based on SNPs of Gcyc1 (Cycloidea), a TCP gene known in patterning the floral dorsoventral asymmetry, we have explored the molecular evolution and genetic differentiation of Gcyc1 at population level, and the population history of C. ramondioides populations distributed in SE China. Eighteen SNPs are detected in 774-bp of the gene, of which eleven are non-synonymous. However, morphological observation of flowers shows that there is no visible differentiation in shape and size across the dorsoventral axis within each whorl. None of the eighteen SNPs is by all shared the eleven populations. Population differentiation is significant. These results reveal that evolution of Gcyc1 at population level is well in accord with the neutral theory. Our study indicates that the SNPs of developmental genes are also useful molecular markers for exploring the genetic differentiation and population history in non-model organisms.     

<Emphasis Type="Italic">WUS</Emphasis> and <Emphasis Type="Italic">STM</Emphasis> homologs are linked to the expression of lateral dominance in the acaulescent <Emphasis Type="Italic">Streptocarpus rexii</Emphasis> (Gesneriaceae)

Acaulescent species of Streptocarpus Lindl. show unusual patterns of growth, characterized by anisocotyly (i.e. the unequal growth of cotyledons after germination) and lack of a conventional embryonic shoot apical meristem (SAM). A SAM-like structure appears during post-embryonic development on the axis of the continuously growing cotyledon. Since we have shown previously that KNOX genes are involved in this unusual morphology of Streptocarpus rexii, here we investigated the expression pattern of WUSCHEL (WUS), which is also required for the indeterminacy of the SAM, but is expressed independently from KNOX in Arabidopsis thaliana. In A. thaliana WUSCHEL is involved in the maintenance of the stem cell fate in the organizing centre. The expression pattern of the WUS ortholog in S. rexii (SrWUS) strongly deviates from that of the model plant, suggesting a fundamentally different spatial and temporal regulation of signalling involved in meristem initiation and maintenance. In S. rexii, exogenous application of growth regulators, i.e. gibberellin (GA₃), cytokinin (CK) and a gibberellin biosynthesis inhibitor (PAC), prevents anisocotyly and relocates meristematic cells to a position of conventional SAMs; this coincides with a re-localization of the two main pathways controlling meristem formation, the SrWUS and the KNOX pathways. Our results suggest that the establishment of a hormone imbalance in the seedlings is the basis of anisocotyly, causing a lateral dominance of the macrocotyledon over the microcotyledon. The peculiar morphogenetic program in S. rexii is linked to this delicate hormone balance and is the result of crosstalk between endogenous hormones and regulatory genes. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Novae Gesneriaceae Neotropicarum XII. New species of Gesneriaceae from the Guianas

Five new species of Gesneriaceae are described from the Guianas:Nautilocalyx coccineus, Paradrymonia anisophylla, andParadrymonia barbata in the tribe Episcieae, from Guyana;Napeanthus angustifolius from French Guiana andNapeanthus rupicola from Guyana in the tribe Napeantheae.     

Characterization of anisocotylous leaf formation in Streptocarpus wendlandii (Gesneriaceae): significance of plant growth regulators

BACKGROUND AND AIMS: Unifoliate species of Gesneriaceae are unique, as they bear only one leaf throughout their life history. The development of this leaf (termed a macrocotyledon) derived from one of two cotyledons is intriguing. The other cotyledon does not develop further and is termed a microcotyledon. This process of unequal cotyledon development is termed anisocotyly. In this study the process of macrocotyeldon formation was studied and the effects of plant hormones on the macrocotyledon development were investigated. METHODS: Streptocarpus wendlandii was chosen as the main subject material, as it was found to be suitable for experimental studies in laboratory conditions. Morphological analyses were carried out with light and scanning electron microscopy. Plant hormones were applied exogenously. KEY RESULTS: The macrocotyledon of S. wendlandii is produced through cell division activity in the basal meristem of the enlarging cotyledon. The newly developed region in the macrocotyledon displayed distinct morphological changes, including the formation of long, needle-shaped trichomes. The newly formed region was surrounded by lateral veins. No such change was observed in the microcotyledon. Furthermore, it was shown that development of anisocotyly is suppressed by the application of cytokinin, resulting in the formation of two nearly equal-sized cotyledons. Both cotyledons displayed macrocotyledon characteristics. This observation in S. wendlandii was confirmed using Monophyllaea glabra, another unifoliate species in the same family. CONCLUSIONS: It is proposed that developmental changes of the macrocotyledon have characteristics of a developmental phase-change, and cytokinins may be involved in its formation. These results are discussed in the light of current knowledge of phase-change transitions in plant vegetative development.