Suzy Huysmans

Orbicules in angiosperms : morphology, function, distribution, and relation with tapetum types

Orbicules, or Ubisch bodies, are sporopollenin particles lining the inner tangential and sometimes also the radial tapetal cell walls. They occur only in species with a secretory tapetum. The surface ornamentation of orbicules and pollen of the same species is often strikingly similar. Although orbicules were discovered more than a century ago, these structures remain enigmatic since their function is still obscure. Proposed hypotheses about their possible function are discussed. We also deal here with topics such as the possible allergenicity of orbicules and their representation in the fossil record. The use of orbicule characters for systematics is reviewed.The distribution of orbicules throughout the angiosperms, based on a literature review from the first report until today, is shown in a list with 314 species from 72 families. Those species found in the literature without orbicules are presented together with their tapetum type. We plotted this information on a dahlgrenogram to visualize the distribution of orbicules. Orbicules occur in all subclasses of the angiosperms. Their occurrence is not correlated with certain modes of pollination or habitats.RésuméLes orbicules, ou corps d’Ubisch, sont des particules de sporopollénine couvrant la surface intérieure tangentiale et parfois la surface radiale des cellules du tapétum. On ne les retrouve que dans les espèces possédant un tapétum sécréteur. L’ornementation superficielle des orbicules et celle du pollen d’une même espèce est souvent remarquablement similaire. Malgré le fait que les orbicules ont été découvert il y a plus d’un siècle, ces structures restent énigmatiques et leur fonction est toujours méconnue. Les hypothèses proposées concernant la fonction éventuelle des orbicules sont commentées dans cet article. Nous avons également traité des sujets tels que les éventuels effets allergènes des orbicules ainsi que leur présence dans les strates fossiles. L’utilisation de caractères orbiculaires dans la systématique est analysée.Nous présentons une liste de 314 espèces appartenant à 72 familles possédant des orbicules, sur base d’une analyse de la litérature à partir de la première observation jusqu’au présent. Pour les espèces rapportées dans la litérature qui ne possèdent pas d’orbicules, nous présentons aussi leur type de tapétum. Nous avons projeté cette information sur un Dahlgrenogramme afin de visualiser la distribution des orbicules. Nous les retrouvons dans toutes les sous-classes des angiospermes. Leur présence n’est pas correlée avec certains modes de pollinisation ou avec divers types d’habitat.

Rapid radiation of Impatiens (Balsaminaceae) during Pliocene and Pleistocene: Result of a global climate change

Impatiens comprises more than 1000 species and is one of the largest genera of flowering plants. The genus has a subcosmopolitan distribution, yet most of its evolutionary history is unknown. Diversification analyses, divergence time estimates and historical biogeography, illustrated that the extant species of Impatiens originated in Southwest China and started to diversify in the Early Miocene. Until the Early Pliocene, the net diversification rate within the genus was fairly slow. Since that time, however, approximately 80% of all Impatiens lineages have originated. This period of rapid diversification coincides with the global cooling of the Earths climate and subsequent glacial oscillations. Without this accelerated diversification rate, Impatiens would only have contained 1/5th of its current number of species, thereby indicating the rapid radiation of the genus.

CARNOY: A new digital measurement tool for palynology

Quantitative data play an important role in palynological research. With the advent of digital imaging in light and electron microscopy, palynologists now have the opportunity to perform measurements faster and more precisely than ever before. Several image analysis software packages already exist for these tasks, but they are often expensive, difficult to use or not adapted to the specific needs of palynologists. After studying the daily workflow of a palynologist, we designed CARNOY, an image analysis application written from the ground up for use in palynology and morphology. CARNOY offers an easy-to-use interface and several features to make measuring easier and faster. The program can export measurements to almost every other software package for further analysis and is available for free on the Internet.

Phylogeny and evolution of Burmanniaceae (Dioscoreales) based on nuclear and mitochondrial data

The mycoheterotrophic Burmanniaceae are one of the three families currently recognized in the order Dioscoreales. Phylogenetic inference using nucleotide sequences of the nuclear 18S rDNA region and the mitochondrial nad1 b-c intron revealed two well-supported, major lineages within the family, corresponding to the two tribes recognized in the family: Burmannieae and Thismieae. All data supported a strong relationship between Thismieae and Tacca (Dioscoreaceae) making both Burmanniaceae and Dioscoreaceae polyphyletic. The three largest Burmanniaceae genera, Burmannia, Gymnosiphon, and Thismia, are paraphyletic. The splitting of Burmanniaceae into Burmannieae and Thismieae indicates two independent origins of mycoheterotrophy and correlated loss of chlorophyll in Dioscoreales. In the genus Burmannia, in which many species still contain chlorophyll, the achlorophyllous species are nested in between the autotrophic species, suggesting many independent changes from autotrophy to heterotrophy or vice versa. A Bayesian relative rates test on the 18S rDNA data showed considerable variation in substitution rates among Burmanniaceae. The substitution rates in all Thismieae and many Burmannieae are significantly faster than in Dioscoreaceae, but there seems to be no correlation between rate increases and the loss of photosynthesis.

A Plastid Gene Phylogeny of the Yam Genus, Dioscorea: Roots, Fruits and Madagascar

Abstract Following recent phylogenetic studies of the families and genera of Dioscoreales, the identification of monophyletic infrageneric taxa in the pantropical genus Dioscorea is a priority. A phylogenetic analysis based on sequence data from the plastid genes rbcL and matK is presented, using 67 species of Dioscorea and covering all the main Old World and selected New World lineages. The analysis used 14 outgroup taxa, including Trichopus Gaertn., Tacca J.R. & G. Forster, Stenomeris Planch., Burmannia L. and Thismia Griff. The main findings are: a) that a clade of rhizomatous taxa is sister to the rest of Dioscorea; b) the main Old World groups (such as the right-twining D. sect. Enantiophyllum) are monophyletic and c) there are two distinct lineages among the endemic Malagasy taxa. The consequences of the results for infrageneric classification of Dioscorea is considered, in particular the possibility of greatly simplifying the classifications of Knuth and Burkill. The results are also used to present novel hypotheses of character evolution in selected underground storage organ, inflorescence, fruit and seed characters and to discuss the origins of diversity in Dioscorea.

Diversification of myco-heterotrophic angiosperms: Evidence from Burmanniaceae

BackgroundMyco-heterotrophy evolved independently several times during angiosperm evolution. Although many species of myco-heterotrophic plants are highly endemic and long-distance dispersal seems unlikely, some genera are widely dispersed and have pantropical distributions, often with large disjunctions. Traditionally this has been interpreted as evidence for an old age of these taxa. However, due to their scarcity and highly reduced plastid genomes our understanding about the evolutionary histories of the angiosperm myco-heterotrophic groups is poor.ResultsWe provide a hypothesis for the diversification of the myco-heterotrophic family Burmanniaceae. Phylogenetic inference, combined with biogeographical analyses, molecular divergence time estimates, and diversification analyses suggest that Burmanniaceae originated in West Gondwana and started to diversify during the Late Cretaceous. Diversification and migration of the species-rich pantropical genera Burmannia and Gymnosiphon display congruent patterns. Diversification began during the Eocene, when global temperatures peaked and tropical forests occurred at low latitudes. Simultaneous migration from the New to the Old World in Burmannia and Gymnosiphon occurred via boreotropical migration routes. Subsequent Oligocene cooling and breakup of boreotropical flora ended New-Old World migration and caused a gradual decrease in diversification rate in Burmanniaceae.ConclusionOur results indicate that extant diversity and pantropical distribution of myco-heterotrophic Burmanniaceae is the result of diversification and boreotropical migration during the Eocene when tropical rain forest expanded dramatically.

Phylogeny of the herbaceous tribe Spermacoceae (Rubiaceae) based on plastid DNA data

Abstract In its current circumscription, the herbaceous tribe Spermacoceae s.l. (Rubiaceae, Rubioideae) unites the former tribes Spermacoceae s. str., Manettieae, and the Hedyotis–Oldenlandia group. Within Spermacoceae, and particularly within the Hedyotis–Oldenlandia group, the generic delimitations are problematic. Up until now, molecular studies have focused on specific taxonomic problems within the tribe. This study is the first to address phylogenetic relationships within Spermacoceae from a tribal perspective. Sequences of three plastid markers (atpB-rbcL, rps16, and trnL-trnF) were analyzed separately as well as combined using parsimony and Bayesian approaches. Our results support the expanded tribe Spermacoceae as monophyletic. The former tribe Spermacoceae s. str. forms a monophyletic clade nested within the Hedyotis–Oldenlandia group. Several genera formerly recognized within the Hedyotis–Oldenlandia group are supported as monophyletic (Amphiasma Bremek., Arcytophyllum Willd. ex Schult. & Schult. f., Dentella J. R. Forst. & G. Forst., Kadua Cham. & Schltdl., and Phylohydrax Puff), while others appear to be paraphyletic (e.g., Agathisanthemum Klotzsch), biphyletic (Kohautia Cham. & Schltdl.), or polyphyletic (Hedyotis L. and Oldenlandia L. sensu Bremekamp). Morphological investigations of the taxa are ongoing in order to find support for the many new clades and relationships detected. This study provides a phylogenetic hypothesis with broad sampling across the major lineages of Spermacoceae that can be used to guide future species-level and generic studies.

Palynological characters and their phylogenetic signal in Rubiaceae

In the 1990s Rubiaceae became a hot spot for systematists, mainly due to the comprehensive treatment of the family by Robbrecht in 1988. Next to the exploration of macromolecular characters to infer the phylogeny, the palynology of Rubiaceae finally received the attention it deserves. This article aims to present a state-of-the-art analysis of the systematic palynology of the family. The range of varíation in pollen morphology is wide, and some of the pollen features are not known from other angiosperm taxa; e.g., a looplike or spiral pattern for the position of apertures in pantoaperturate grains. We compiled an online database at the generic level for the major pollen characters and orbicule presence in Rubiaceae. An overview of the variation is presented here and illustrated per character: dispersal unit, pollen size and shape, aperture number, position and type, sexine ornamentation, nexine pattern, and stratification of the sporoderm. The presence/absence and morphological variation of orbicules at the generic level is provided as well. The systematic usefulness of pollen morphology in Rubiaceae is discussed at the (sub)family, tribal, generic, and infraspecific levels, using up-to-date evolutionary hypotheses for the different lineages in the family. The problems and opportunities of coding pollen characters for cladistic analyses are also treated.

Pollen morphology of NW European representatives confirms monophyly of Rubieae (Rubiaceae)

Abstract This study focuses on the six genera of Rubieae that occur in NW Europe: Asperula, Crucianella, Cruciata, Galium, Rubia, and Sherardia. The pollen morphology of 29 species was studied using light microscope and scanning electron microscope observations. Several features demonstrate the advanced nature of the tribe: simple apertures, up to 13 ectocolpi, supratectal microspines, a characteristic and unique endopattern, and absence of orbicules. Asperula, Cruciata, Galium, and Rubia cannot be distinguished by pollen morphology only. The monospecific genus Sherardia can be recognized easily by the high numbers of apertures (10–13) that are slit-like and the very fine perforations in the tectum. Some Crucianella species have relatively larger perforations in the tectum. None of the species investigated produces orbicules, which makes Rubieae, next to Gardenieae, the second rubiaceous tribe entirely without orbicules. Our palynological data are interpreted in the broader perspective of all herbaceous Rubiaceae. The Rubieae are unique among Rubiaceae in the combination of the following pollen features: several colpate apertures, a perforate and microechinate tectum, a relatively small size, the absence of endoapertures, a coarse nexine area beneath the ectocolpi, and the absence of orbicules. The predictive value of pollen morphology is therefore extremely high at the tribal level and supports the monophyly of Rubieae.

Pistillata—Duplications as a Mode for Floral Diversification in (Basal) Asterids

Basal asterid families, and to a lesser extent the asterids as a whole, are characterized by a high variation in petal and stamen morphology. Moreover, the stamen number, the adnation of stamens to petals, and the degree of sympetaly vary considerably among basal asterid taxa. The B group genes, members of the APETALA3 (AP3) and PISTILLATA (PI) gene lineages, have been shown to specify petal and stamen identities in several core eudicot species. Duplicate genes in these lineages have been shown in some cases to have diversified in their function; for instance in Petunia, a PI paralog is required for the fusion of stamens to the corolla tube, illustrating that such genes belonging to this lineage are not just involved in specifying the identity of the stamens and petals but can also specify novel floral morphologies. This motivated us to study the duplication history of class B genes throughout asterid lineages, which comprise approximately one-third of all flowering plants. The evolutionary history of the PI gene subfamily indicates that the two genes in Petunia result from an ancient duplication event, coinciding with the origin of core asterids. A second duplication event occurred before the speciation of basal asterid Ericales families. These and other duplications in the PI lineage are not correlated with duplications in the AP3 lineage. To understand the molecular evolution of the Ericales PI genes after duplication, we have described their expression patterns using reverse transcription polymerase chain reaction and in situ hybridization, reconstructed how selection shaped their protein sequences and tested their protein interaction specificity with other class B proteins. We find that after duplication, PI paralogs have acquired multiple different expression patterns and negative selective pressure on their codons is relaxed, whereas substitutions in sites putatively involved in protein-protein interactions show positive selection, allowing for a change in the interaction behavior of the PI paralogs after duplication. Together, these observations suggest that the asterids have preferentially recruited PI duplicate genes to diverse and potentially novel roles in asterid flower development.