Breeding system and fruit set in African Marantaceae

Marantaceae are a pantropically distributed family of perennial herbs and lianas in the understory of tropical rainforests. They are characterized by a unique pollen transfer mechanism. To understand its functional significance and evolution, field investigations have been conducted in Gabon.Data from 28 (of 35) species from Central Africa are achieved. The pollen–ovule ratio (34–140:1; exception Sarcophrynium 2.5:1) falls into the range of facultative autogamous species. All investigated species were proven to be self-compatible; however, only two were autogamous. Natural fruit set was generally low (10.9 ± 10%). The highest natural fruit set was found in Marantochloa purpurea (29.7%), Ma. grandiflora (33.5%) and the two autogamous species Halopegia azurea (31%) and Marantochloa leucantha (35%). Considerable higher fruit set could be reached in all species by hand-self-pollination.We conclude that autogamy is generally avoided through herkogamy based on secondary pollen presentation on the back of the style head – a central component of the specific pollen transfer mechanism. However, with respect to the consecutive visit of pollinators to several flowers of the same individual geitonogamy cannot be excluded. The aggregated pollen transfer via the explosive pollination mechanism might be interpreted as an adaptation to low pollinator visitation rate, pollen limitation might explain the low fruit set.     

The puzzling ecology of African Marantaceae forests

Marantaceae forests are tropical rainforests characterized by a continuous understory layer of perennial giant herbs and a near absence of tree regeneration. Although widespread in West-Central Africa, Marantaceae forests have rarely been considered in the international literature. Yet, they pose key challenges and opportunities for theoretical ecology that transcend the borders of the continent. Specifically, we ask in this review whether open Marantaceae forests and dense closed-canopy forests can be considered as one of the few documented examples of alternative stable states in tropical forests. First, we introduce the different ecological factors that have been posited to drive Marantaceae forests (climate, soil, historical and recent anthropogenic pressures, herbivores) and develop the different hypotheses that have been suggested to explain how Marantaceae forests establish in relation with other vegetation types (understory invasion, early succession after disturbance, and intermediate successional stage). Then, we review the underlying ecological mechanisms that can explain the stability of Marantaceae forests in the long term (tree recruitment inhibition, promotion of and resilience to fire, adaptive reproduction, maintenance by megaherbivores). Although some uncertainties remain and call for further empirical and theoretical research, we found converging evidence that Marantaceae forests are associated with an ecological succession that has been deflected or arrested. If verified, Marantaceae forests may provide a useful model to understand critical transitions in forest ecosystems, which is of particular relevance to achieve sustainable forest management and mitigate global climate change.     

Pollination, breeding system and seed abortion in some African acacias

TYBIRK, K., 1993. Pollination, breeding system and seed abortion in some African acacias . Studies of the flower visitors and pollination ecology of Acacia albida Del., A. nilotica (L.) Willd. ex Del. A. tortilis (Forssk.) Hayne and A. Senegal (L.) Willd. in Senegal and Kenya showed a high diversity of floral foragers. One hundred and eighteen taxa of insects mainly from Hymenoptera, Lepidoptera, Coleoptera and Diptera were collected. The most important pollen vectors were bees from the families Megachilidae and Halictidae, and wasps from the families Scoliidae and Eumenidae. Beetles, flies and butterflies were secondary pollen vectors. Diversity and frequency of flower visitors of species with floral nectar ( A. Senegal and A. albida ) were not clearly different from species without floral nectar ( A. tortilis, A. nilotica ). Acacia tortilis was almost exclusively outcrossed (Index of Self Incompatibility = 0.2), with 5.5% of the inflorescences (0.13% of the flowers) developing fruits. The number of seeds per pod was positively correlated with dispersal type. Wind dispersed species had fewer seeds per pod than animal dispersed species. About 5% of the seeds were aborted in A. tortilis and A. nilotica , while 22–48% of the seeds were aborted in A. Senegal, A. ataxacantha DC. and A. polyacantha Willd. Most abortions in the latter three species occur in the proximal end of the pods, indicating selective seed abortion.     

Bimodal Pollination by Wasps and Beetles in the African Milkweed Xysmalobium undulatum

It has been suggested that flowers of some plants are specialized for pollination by two unrelated species (or functional groups) of pollinators. However, evidence for 'bimodal pollination systems' has been extremely limited. Studies of the milkweed Xysmalobium undulatum in South Africa showed that its flowers are visited by a range of different insects (representing 18 families), but only two groups, represented by the chafer beetle Atrichelaphinis tigrina and pompilid wasps in the genus Hemipepsis , effect pollination. Experiments showed that both these pollinator groups are effective in removing and inserting pollinia. Pollinia are attached to clypeal hairs and mouthparts on the wasps and tarsal hairs and spines on the beetles. Although considerably less abundant than the beetles, Hemipepsis spp. wasps move more quickly among flowers and appeared to be more effective pollinators overall. Experimental hand-pollinations conducted in the field showed that X. undulatum is genetically self-incompatible and thus completely reliant on pollinators for reproduction. We conclude that X. undulatum has a bimodal pollination system, specialized for pollination by Hemipepsis pompilid wasps and the chafer beetle A. tigrina .     

Phylogeny and classification of Marantaceae

Relationships of Marantaceae were estimated from nucleotide sequence variation in the rps16 intron (plastid DNA) and from morphological characters. Fifty-nine species (21 genera) formed the ingroup, and 12 species (12 genera) of other Zingiberales formed the outgroup. There is no support for the traditional subdivision of Marantaceae into a triovulate and a uniovulate tribe or the informal groups previously proposed. The so-called Donax group forms a paraphyletic grade that is basal within Marantaceae. Thalia appears as the distal branch of this grade, but its position is not supported in jackknife analysis. The so-called Calathea group is monophyletic in all shortest trees but not supported with greater than 50% jackknife. The genus Calathea appears to be paraphyletic. The Maranta and Phrynium groups are clearly polyphyletic. Maranta, Koernickanthe , and genera of the Mymsma group, all neotropical, form a strongly supported monophyletic group. The sister of this group is the palaeotropical genus Halopegia. Koernickanthe is nested within Maranta , as this genus is traditionally circumscribed. The African genera Ataenidia and Marantochloa form a strongly supported clade in which Ataenidia is the sister group to Marantochloa . Based on phylogeny it is concluded that Africa, in spite of being much poorer in species, is the most likely ancestral area of Marantaceae     

Nomenclatural notes on neotropical Marantaceae

Two new combinations are made:Stromanthe macrochlamys (Woodson & Standley), transferred fromCalathea, andCtenanthe amabilis (Morren), transferred fromStromanthe. Calathea crotalifera S. Watson from Guatemala is an earlier name forC. insignis Petersen.     

利用传粉综合征预测:长瓣兜兰模拟繁殖地欺骗雌性食蚜蝇传粉

在花部进化受传粉者主导这一经典理论影响下,传粉综合征一直被认为是被子植物对应于某些特定传粉者的标志,因此,可以利用传粉综合征来预测传粉者。近年来,这种对应和预测受到多因素影响,以及花部进化理论和传粉者泛化理论的冲击。在本研究中,我们选择长瓣兜兰Paphiopedilum dianthum作为实验材料,来探讨传粉综合征与传粉者的关系以及利用前者预测后者的有效范围。长瓣兜兰具有的一系列特征,同其他依靠假繁殖地欺骗食蚜蝇传粉的兜兰种类相似,包括倒盔状唇瓣,较大的中萼片以及花瓣上的黑色突起和睫状毛,而且长瓣兜兰同这些种类有很近的亲缘关系和相似的生境。根据传粉综合征概念,长瓣兜兰应该是由食蚜蝇传粉,通过模拟繁殖地来欺骗传粉者。为了检验这些预测,我们对长瓣兜兰进行了传粉生物学研究。长瓣兜兰是自交可亲和的物种,不存在自动自交授粉现象,必须依靠昆虫传粉才能结实。结果表明,雌性黑带食蚜蝇Episyrphus balteatus是长瓣兜兰的主要传粉者,并且这种兜兰是通过模拟繁殖地来欺骗食蚜蝇传粉的。根据本实验结果,我们认为传粉综合征只是对应于不同的传粉选择压力而不是简单对应于传粉者种类,而使用传粉综合征预测时还需要考虑生境和演化历史等因素对花部形态的影响,这样才可能得到有效的结果。     

Leaf movement in Calathea lutea (Marantaceae)

Summary Calathea lutea is a broad-leaved, secondary successional plant which shows complex leaf movements involving both elevation and folding of the leaf surface about the pulvinus. In the plants studied, mean leaf elevation increased from approximately 34 degrees in the early morning to 70 degrees at noon while the angle of leaf folding increased from 13 degrees to 50 degrees over the same time period. During the period from early morning to noon, these movements resulted in a significant decrease in the cosine of the angle of incidence, a measure of the direct solar radiation intercepted. The observed changes in elevational angle significantly reduce the cosine of angle of incidence while folding does not significantly reduce the fraction of direct solar radiation intercepted during the period of direct exposure of the leaf surface to the solar beam. Since elevational changes seem to account for the reduction in exposure to direct solar radiation, the role of folding remains unclear.     

Pollination syndromes predict brood-site deceptive pollination by female hoverflies in Paphiopedilum dianthum (Orchidaceae)

In order to explore the relationship between the pollinator and pollination syndromes, and to evaluate the possibility of predicting likely pollinators based on pollination syndromes, the pollination biology of Paphiopedilum dianthum was examined. This species shares a close phylogenetic relationship, similar habit, and a recognizable syndrome of floral features (including helmet-shaped labellum, big dorsal sepal, and black warts or hairs on petals) with other brood-site deceptive Paphiopedilum species. According to the pollination syndrome concept, P. dianthum would be pollinated by hoverflies and attract pollinators with brood-site deception. Results were consistent with this prediction. Paphiopedilum dianthum was mainly pollinated by female hoverflies (Episyrphus balteatus), and these flies were indeed lured by the false brood-site on the orchid flower. It is suggested that the pollination syndrome may be correlated with pollination selective pressure, but not simply with pollinator species, and that accurate prediction requires consideration of all factors influencing floral characters, including habit and evolutionary history.     

Setting-up tension in the style of Marantaceae

The Marantaceae stand out from other plant families through their unique style movement which is combined with a highly derived form of secondary pollen presentation. Although known for a long time, the mechanism underlying the movement is not yet understood. In this paper, we report an investigation into the biomechanical principles of this movement. For the first time we experimentally confirm that, in Maranta noctiflora, longitudinal growth of the maturing style within the 'straitjacket' of the hooded staminode involves both arresting of the style before tripping and building up of potential for the movement. The longer the style grows in relation to the enclosing hooded staminode, the more does its capacity for curling increase. We distinguish between the basic tension that a growing style builds up normally, even when the hooded staminode is removed beforehand, and the induced tension which comes about only under the pressure of a too short hooded staminode and which enables the movement. The results of our investigations are discussed in relation to previous interpretations, ranging from biomechanical to electrophysiological mechanisms.     

Notes on Ischnosiphon (Marantaceae)

Four new species are described, viz. Ischnosiphon bahiensis (Brazil), I. ursinus (French Guiana and Rio Negro Basin), I. crassispicus (vicinity of Manaus), and I. fusiformis (NE Peru). New data on ecology, morphology, or distribution are presented for I. inflatus Anderss., I. enigmaticus Anderss., I. centricifolius Anderss., I. gracilis (Rudge) Koern., I. helenae Anderss., I. macarenae Anderss., I. polyphyllus (P. & E.) Koern., and I. surumuensis Loes. The typification of I. arouma (Aubl.) Koern. is briefly discussed.     

Pollination in conifers

Our understanding of pollination in conifers has advanced rapidly in recent years, but it still lags behind our knowledge of this process in angiosperms. In part this is because conifers are not considered to be high priority crops and, unlike many cultivated flowers, conifer seed cones are generally neither large nor colorful. The use of genetics to improve tree growth has primarily been through selection and asexual propagation rather than breeding, and because incompatibility is not thought to occur in conifer pollination systems, concern about pollination has primarily been with regard to seed production. Here we examine the ancestral wind-pollination mechanism in conifers and discuss how the process may have evolved to improve pollination success.     

Anatomic insights into the thigmonastic style tissue in Marantaceae

The irreversible style movement in Marantaceae is one of the quickest plant movements ever recorded. It is largely based on a special tissue construction, which is analysed herein for the first time. Histological sections, fluorescence and different electron microscopic techniques are used to study the style tissue of eight species in six genera of the Marantaceae. Tissue sections prior to the thigmonastic movement are only obtained after ether or chloroform narcosis. The tissue in the bending zone of the style has the construction of a lamellar collenchyma with elongated cells and extended intercellular spaces. The thicker cell walls abut the intercellular spaces, while the thinner walls between adjacent cells are extraordinarily porous. The tissue is thus characterised by strongly perforated cell bundles which are able to slide alongside each other and the intercellular spaces. Cell-wall loosening starts about 24 h before flowering and is interpreted as a result of enzymatic ageing processes. It is also found in other members of the Zingiberales, but only the Marantaceae take advantage of the maceration process. We conclude that the specific tissue construction contributes to the rapid style movement. It combines qualities for stabilisation (collenchyma), pliability (intercellular spaces) and water transport (extremely porous tissue), thus supporting the irreversible style bending by a sudden and final shift of fluid.     

Spatially limited clonality and pollen and seed dispersal in a characteristic climber of Central African rain forests: Haumania danckelmaniana (Marantaceae)

Gene dispersal and clonality are important aspects of plant evolution affecting the spatial genetic structure (SGS) and the long‐term survival of species. In the tropics these parameters have mostly been investigated in trees and some herbs, but rarely in climbers which frequently: (1) show clonal growth leading to a patchy distribution pattern similar to that of understory herbs; and (2) flower in the canopy where they may have access to long‐distance dispersal like canopy trees. We thus hypothesize for climbers an intermediate genetic structure between herbs and trees. The study aims at assessing breeding system and spatial extent of clonality and gene dispersal in Haumania danckelmaniana (Marantaceae), a common climber in the tropical rain forests from western Central Africa. In eastern Cameroon, 330 ramets were sampled at three spatial scales and genotyped at seven microsatellite loci. Clonality was moderate (clonal extend: 15–25 m, clonal diversity 0.4–0.65) indicating the importance of recruitment from seeds at this locality. The low inbreeding (F_IS) suggested predominant outcrossing. The rate of decay of the relatedness between individuals with distance indicated limited gene dispersal distance (σ_g = 9–50 m, neighborhood sizes Nb = 23–67) in accordance with narrowly gravity dispersed seeds and restricted pollen transfer distance in densely flowering populations. The marked SGS (Sp = 0.011–0.026) was similar to that reported in tropical trees, but might increase with augmented clonality as in many herbs, especially under more severe disturbance regimes.     

Sanblasia, a new genus of the Marantaceae

Sanblasia dressleri is described from material from the Serranía de San Blas, E Panamá. The inflorescence has the general appearance of an Ischnosiphon , but the ovary is 3–ovulate, as in Calathea , and the bracteole is channeled and keeled, as in many species of Calathea , and in Pleiostachya.     

Additional Ecuadorian species in Calathea series Comosae (Marantaceae)

Three new species in Calathea series Comosae (Petersen) Schumann are described from Ecuador: Calathea pallidicosta, C. attenuata and C. lagoagriana. Calathea pallidicosta is currently known only from Ecuador, C. lagoagriana occurs in both Colombia and Ecuador while C. attenuata is more widespread, occurring in Colombia, Ecuador, Perú and Brasil. Calathea attenuata and C. pallidicosta are in the monomorphic-bracted group of C. series Comosae while C. lagoagriana is in the dimorphic-bracted group. Calathea lagoagriana possibly hybridizes with C. loeseneri Macbride.     

少花柊叶传粉生物学的研究

竹芋科Marantaceae植物所具有的雄蕊先熟(protandry)、次级花粉展示(secondary pollen presentation)以及不可逆转的爆发性花柱运动(explosive style movement)等特点,造就了其独特的传粉机制.本文对竹芋科多年生草本植物少花格叶Phrynium oliganthum的花生物学特性、传粉操控实验和传粉者行为观察三个方面做了较为系统的研究,以掌握该植物基本的开花行为及繁殖特性.实验结果表明,少花格叶自交亲和,但不存在自动自交机制,其传粉过程依赖于传粉者.传粉者为每天沿固定路线访花、被称为有序觅食者(trapliner)的独居蜂类(无垫蜂Amegilla spp.).在传粉实验中,无论是人工授粉还是自然状态下坐果率都很低(<10%),这可能是由于资源限制以及严重的花序腐烂及虫食.少花柊叶每天开花数约11朵,但并不同步,而是在4h内逐次开放,这种开花格局连同传粉者在一天之内会重复同一线路的拜访特点,有利于少花格叶在一定程度上减少同株异花授粉的发生,增加异交的机会.