Pollen morphology of Xanthium L. (s.l.) (Asteraceae,Asteroideae, Heliantheae,Ambrosiinae) in the Iberian Peninsula - a palynotaxonomic approach to a poisonous,allergenic and invasive genus

Abstract

The pollen morphology of the Iberian taxa of the genus Xanthium s.l. and of the non-Iberian species X. ambrosioides was studied to help to identify these poisonous, allergenic and invasive taxa and clarify their taxonomic relationships. In addition, the question of the existence and structure of a mesoaperture in the apertural system of Xanthium was also considered. The pollen grains of sections Acanthoxanthium and Xanthium clearly differ by their characters, which supports the separation of both taxa and allows for their distinction based on pollen morphology. It is suggested that the morphological and palynological differences between Xanthium and Acanthoxanthium, together with the lack of hybridisation between the two sections and the monophyly of Acanthoxanthium, could lead to the elevation of the latter to the generic status. The two species of section Xanthium present in the Iberian Peninsula (X. orientale and X. strumarium) and of section Acanthoxanthium are well separated by their palynological features. Likewise, the Iberian subspecies of Xanthium, X. orientale subsp. orientale and X. orientale subsp. italicum are palynologically distinguishable. However, no significant difference could be found between the pollen of X. strumarium subsp. strumarium and of X. strumarium subsp. brasilicum. The pollen data do not support the hypotheses of a hybrid origin for X. strumarium subsp. brasilicum. A mesoaperture intersecting the foot layer and the upper part of the endexine is present in both sections, which is congruent with the results already found for other Asteroideae.     

Paleobotanical remains from the Paleocene–lower Eocene Vagadkhol Formation, western India and their paleoclimatic and phytogeographic implications

A small assemblage of macro- and micro floral remains comprising fossil leaf impressions, silicified wood, spores, and pollen grains is reported from the Paleocene–lower Eocene Vagadkhol Formation (=Olpad Formation) exposed around Vagadkhol village in the Bharuch District of Gujarat, western India. The fossil leaves are represented by five genera and six species, namely, Polyalthia palaeosimiarum (Annonaceae), Acronychia siwalica (Rutaceae), Terminalia palaeocatapa and T. panandhroensis (Combretaceae), Lagerstroemia patelii (Lythraceae), and a new species, Gardenia vagadkholia (Rubiaceae). The lone fossil wood has been attributed to a new species, Schleicheroxylon bharuchense (Sapindaceae). The palynological assemblage, consisting of pollen grains and spores, comprises eleven taxa with more or less equal representation of pteridophytes, gymnosperms, and angiosperms. Angiospermous pollen grains include a new species Palmidites magnus. Spores are mostly pteridophytic but some fungal spores were also recovered. All the fossil species have been identified in the extant genera. The present day distribution of modern taxa comparable to the fossil assemblage recorded from the Vagadkhol area mostly indicate terrestrial lowland environment. Low frequency of pollen of two highland temperate taxa (Pinaceae) in the assemblage suggests that they may have been transported from a distant source. The wood and leaf taxa in the fossil assemblage are suggestive of tropical moist or wet forest with some deciduousness during the Paleocene–early Eocene. The presence of many fungal taxa further suggests the prevalence of enough humidity at the time of sedimentation.     

Pollen morphology and its taxonomic significance of the monotropoideae (Ericaceae)

A palynological survey, including LM, SEM and TEM is presented for eight genera, nine species and 76 samples of the Monotropoideae which is composed of 10 genera and 13 species. On the basis of the aperture number and shape, the following six pollen types are recognized: 1) 3-colp(oroid) ate—Allotropa, 2) 2-colpor(oid)ate—Monotropsis andHemitomes, 3) 4-colpor(oid)ate—Pterospora, Sarcodes andPleuricospora, 4) 2- and 3-colpor(oid)ate—Monotropa hypopitys, 5) 3-colporate and-porate —Monotropa uniflora, 6) 3- to 4- porate—Monotropastrum humile. Relationships among taxa within the Monotropoideae are illustrated on the palynological characters including the aperture type, exine sculpture and structure. Both pollen grains with two and four apertures have evolved independently from pollen grains with three apertures, according to the infraspecific variation of aperture numbers and the usual occurrence of three-aperturate pollen grains in the Ericaceae. 3-colp(oroid)ate pollen ofAllotropa is the most primitive and occupies an isolated position in the subfamily, on the other hand 3- to 4-porate pollen ofMonotropastrum humile is most advanced in the subfamily, probably even in the Ericaceae. A reduced sexine inMonotropastrum humile appears to be a specialized pollen character. Infraspecific geographical difference in palynological characters is revealed in two species ofMonotropa for the first time.M. hypopitys is basically characterized by pollen grains with two apertures in the New World vs. three apertures in the Old World.M. uniflora is basically characterized by 3-porate pollen in the New World vs. 3-colporate in the Old World. In both species pollen grains with more primitive characters usually occur in the Old World.     

FINE STRUCTURE OF MISTLETOE POLLEN. V. MADAGASCAN AND CONTINENTAL AFRICAN VISCUM L. (VISCACEAE)

Pollen characters of Madagascan and continental African Viscum are described and compared to those in Asia and Australia. The subprolate, tricolporate, nonuniformly sculptured pollen of Madagascan taxa is most similar to that of Asian species. Ultrastructurally, however, the completely granular equatorial ektexine of Madagascan Viscum is most similar to that of continental African taxa. Continental African Viscum, in contrast to Madagascan and Asian species, display a wide variation in pollen shape and apertures. Pollen shape ranges from subprolate to oblate, the latter unique to Africa. The most striking feature of continental Viscum is their variability in aperture number and aperture type. Aperture number varies at both the intra- and interpopulational levels with such variation resolvable to the individual flower—a condition unique to the continent. The only simple (colpate) aperture type in the genus is restricted to Africa. The continental species can be divided into two species groups based on pollen characters: Group I (4 spp.) characterized by strictly tricolporate rounded convex pollen with a rodlet/granular equatorial ektexine structure and Group II (most continental species) possessing multiapertures, concave lobate shape, uniform sculpturing and granular equatorial ektexine. The African V. menyharthii, V. fischeri, V. rotundifolium and V. minimum exhibit no clear Group I or II affinities. An analysis of overall pollen characters in Viscum indicates a trend towards spheroidal shape, multiapertures and uniform sculpturing and ektexine organization. Though pollen characters suggest ties between Australia, Asia and Madagascar, they indicate an even stronger relationship between Madagascar and continental Africa, particularly eastern Africa. The relationship of the majority of African Viscum, excluding those with obvious Madagascan affinities, remains obscure. The unique palynological features of Group II species coupled with their inflorescence structure suggest an independently evolving group.     

Some evidence for infrageneric classification in Ziziphora L. (Lamiaceae:Mentheae)

The genus Ziziphora L. (Lamiaceae) consists of annual herbs, except Ziziphora clinopodioides, and is represented by six taxa in the flora of Turkey: Z. clinopodioides, Z. capitata, Z. persica, Z. tenuior, Z. taurica subsp. taurica and Z. taurica subsp. cleonioides. They are strong aromatic herbs and important medicinal plants. This study has been conducted to determine the palynological and karyological features of these taxa. The pollen morphology and exine structure of Ziziphora species were investigated by light microscope and scanning electron microscope. Pollen grains were determined as hexacolpate, medium in size and a circular or elliptic amb. The shape of pollen grains varies from oblate to prolate spheroidal. Ornamentation types of pollen grains are bireticulate, microreticulate or perforate. Somatic chromosome number has been determined and counted as 2n = 16, 18. Results indicate that the pollen characters and chromosome numbers of the genus are valuable for taxonomic applications and may be useful for infrageneric classification.     

Distyly and pollen dimorphism in<Emphasis Type="Italic"> Damnacanthus</Emphasis> (Rubiaceae)

We document distyly in Damnacanthus (Rubiaceae) and investigate pollen morphology in the genus. Within nine taxa in Japan (four species, four varieties and one form), five show distyly. Non-distylous taxa of Damnacanthus always have a long style and short stamens. We examined the pollen morphology of all taxa of Damnacanthus in Japan. The pollen grains of Damnacanthus are 3- to 5-orthocolporate or sometimes loxocolporate. Polymorphic pollen is sometimes observed even within a single flower. Pollen dimorphism is associated with distyly; pollen grains from short-styled (thrum) flowers are significantly larger than those from long-styled (pin) flowers, and the muri are smooth in pin flowers whereas the pollen grains of thrum flowers have minute granules on the top and/or on the sides. In non-distylous taxa, in which the style is longer than stamens, the muri are always provided with minute granules. Interestingly, the pollen grains with granules in the non-distylous taxa contrast with the pollen of the distylous taxa, because granulate pollen grains are found only in thrum flowers. Although Damnacanthus is a stenopalynous genus, the number of colpi is useful for delimiting taxa. Based on palynological characters, we conclude that Damnacanthus should be revised. Electronic Publication     

Palynological study of Potentilla subg. Potentilla (Rosaceae) in the Western Mediterranean

A palynological study by LM and SEM was made of 26 taxa of Potentilla L. subg. Potentilla. It is more precise on material from 110 populations, mainly from the western Mediterranean. On the basis of morphometry, the subg. Potentilla can be said to have a stenopalynous nature, due to the absence of significant differences between the taxa studied and to the high degree of overlapping shown by their range of variation. With respect to ornamentation, which is striate, only P. rupestris pollen can be separately identified by a much more marked striation than the other species studied. An attempt was made to observe the taxonomic and phylogenetic relationships between the species of the natural groups of Potentilla on the basis of their pollen characters.     

The metareticulate pollen morphology of Alternanthera Forssk. (Gomphrenoideae,Amaranthaceae) and its taxonomic implications

Alternanthera (Amaranthaceae) is a diverse genus largely restricted to the American Tropics that belongs to the alternantheroid clade containing C₄ and C₃–C₄ intermediate species. This research focuses on the study of pollen characters by studying 13 species, representatives of the two major clades and subclades of Alternanthera. General palynological comparisons were conducted with light microscopy (LM), scanning electron microscopy (SEM) and with confocal laser scanning microscopy (CLSM) for exine ultrastructure. Twenty-five characters were measured and described for Alternanthera and among these, 14 pollen characters were used to discriminate pollen groups using cluster analysis and canonical analysis of principal coordinates (CAP). Pollen form and ornamentation, pores number, spines length, number of ektexinous bodies and nanospines on the ektexinous bodies on pore membranes, arrangement of nanopores and spines on structural elements, and metareticula form were taxonomically important and therefore used to construct the first palynological key to the alternantheroid clade species. Our study indicates that the seemingly subtle morphological variation of pollen is useful for recognising three main pollen types within Alternanthera. The much needed palynological terminology for describing the mesoporium in the metareticulate pollen of Amaranthaceae is provided.     

Pollen morphology and phylogenetic analysis of Eperua Aublet (Detarieae: Caesalpinioideae: Leguminosae)

The diverse pollen morphology of fourteen species of the genus Eperua is described and illustrated using light, scanning electron and transmission electron microscopy. Six pollen types are described and a key for their identification is provided. A cladistic analysis was carried out using macromorphological and palynological characters to form a hypothesis of relationships between taxa. The pollen morphology is discussed with regard to systematic relationships, function and phylogenetic significance of certain pollen morphological structures within the genus.     

POLLEN MORPHOLOGY AND ULTRASTRUCTURE OF KRAMERIA (KRAMERIACEAE): UTILITY IN QUESTIONS OF INTRAFAMILIAL AND INTERFAMILIAL CLASSIFICATION

The genus Krameria is currently recognized as an enigmatic, monotypic family of dicotyledons. Previous studies of morphology, anatomy, and cytology have been unable to establish unequivocably its phyletic affinities. We report here the results of an intensive investigation of the pollen of Krameria using light, scanning electron (SEM), and transmission electron microscopy (TEM). Pollen characteristics of the genus were compared to those of all families referred to the Polygalales and to selected species of the Leguminosae-Caesalpinoideae, both groups with which Krameria has historically been allied. Superficially, the pollen of Krameria resembles that of the legumes more than that of genera in the Polygalales. However, in ultrastructure, it differs from the pollen of all taxa investigated from both groups. Within Krameria, several variations of a basic type of 3-colporate pollen are discernible. Species with similar pollen variants appear, on the basis of other morphological data, to represent natural groups within the genus. Nevertheless, an arrangement of groups of species of Krameria from “least” to “most” specialized, based on a logical sequence of modification of the pollen morphology, does not agree with any sequence of specialization using other morphological or ecological characters. It is concluded that pollen morphology and ultrastructure has systematic value for intrafamilial groupings of the Krameriaceae but that palynological modifications are incongruous with trends of specializations of other characters and, like many other lines of investigation, pollen studies do not provide significant data as to the phylogenetic affinities of the family.     

Morphological studies of pollen grains of the Polish endemic species of the genus <Emphasis Type="Italic">Rubus</Emphasis> (Rosaceae)

The pollen of six taxa of the genus Rubus endemic to Poland (R. capitulatus, R. chaerophylloides, R. ostroviensis, R. posnaniensis, R. seebergensis and R. spribillei)was studied using light and scanning electron microscopy. The study objective was to extend the knowledge of the species pollen morphology and to investigate whether pollen morphology may help to taxonomically distinguish a very rare bramble species. Study material was derived from six natural localities where the species occur in the Wielkopolska region (Poland). Ten quantitative pollen grain features were analysed as well as the following qualitative ones: outline, shape, type of bridge and exine sculpture. Only mature, correctly formed pollen grains (30 per specimen) were measured and 180 pollen grains were examined in total. It was found that R. capitulatus and R. seebergensis had the highest mean values of P, E and Le features. In addition, pollen grains of R. capitulatus were most flattened (mean P/E ratio equals 1.14), while those of R. seebergensis were most elongated (mean P/E ratio equals 1.27). R. spribillei was the only species with striae of similar width as muri, whereas striae in the remaining species were wider. R. chaerophylloides and R. posnaniensis were characterised by specific, similar exine sculpture. Nevertheless, it should be stated that differences between pollen features of the species studied are so small and the variability of these features are so large that it is difficult to clearly identify the species studied. Therefore, pollen grain morphology can serve only as an auxiliary feature for the determination of these species.     

Palynological study of the Venezuelan species of the genus <Emphasis Type="Italic">Hymenocallis</Emphasis> (Amaryllidaceae)

Pollen morphology and exine structure of the seven Hymenocallis Salisb. species present in Venezuela were investigated using scanning (SEM) and transmission (TEM) electron microscopy. Pollen grains of all species are monosulcate, heteropolar, with bilateral symmetry, oblate to peroblate, heterobrochate, semitectate-columellate, possess unequal tectal surfaces, and are clavate or baculate when viewed with TEM. They present two equatorial apexes. When observed under SEM their surfaces appear as granulate; however, it is evident from TEM that they are in fact constituted by pila. All the species possess very large pollen (ranging from 64 to 85 μm and from 125 to 155 μm for polar and equatorial axes, respectively), and no relationship was evident between pollen size and chromosome number. All the taxa are also very similar in relation to their pollen outline, ornamentation and internal structure, thus indicating that the genus is accurately delimited from the palynological point of view and that discrete characteristics can only be used in some cases to delimit individual species.     

Buxus sirindhorniana sp. nov. (Buxaceae), a bicarpellate species from Thailand

A new bicarpellate Buxus species, Buxus sirindhorniana W. K. Soh, M. von Sternburg, Hodk. & J. Parn., is described from northern Thailand. This is the first reported bicarpellate species of Buxus. The pollen morphology and the degree of pollen viability of the species are reported. DNA was extracted from herbarium samples and the internal transcribed spacer (ITS) region of nuclear ribosomal DNA sequenced. The palynological evidence and the phylogenetic reconstruction support the contention that this new species belongs to the genus Buxus. The morphological diversity of reproductive organs in the Buxaceae, in relation to this new species, is briefly discussed.     

Biosystematic study of the genus <Emphasis Type="Italic">Berberis</Emphasis> L. (Berberidaceae) in Khorassan,NE Iran

Four species of the genus Berberis L. have been reported from different regions, including Khorassan provinces. In this article, a revision of this genus in Khorassan provinces is presented. For better validation of the results, morphological, palynological, chromosomal and molecular studies were conducted on specimens collected from Khorassan provinces and preserved in FUMH and TARI herbaria. Morphological study resulted in recognition of three species of Berberis, from which two species are new records for Khorassan. Four unknown new taxa with new morphological characters were also identified, but left for further analysis because of the high percentage of polyploidy and hybridization in this genus. In order to analyze morphological data, 35 OTUs were provided and scored using the distance method and PCoA. The shape and size of pollen grains were nearly equal in the examined taxa, and there were no obvious differences between them. Chromosomal examination indicated tetraploidy (2n = 4x = 56) in all of the studied taxa. Molecular studies were accomplished by RAPD and sequencing of the ITS region to construct a framework of relationships between the taxa. Molecular studies emphasized the difference in the four unknown taxa from others. The total evidence indicates that Berberis L. shows a high percentage of polyploidy and hybridization.     

A comparative study on two closely relative Tulipa L. taxa from NE Anatolia

This study presents observations on the anatomical, palynological and ecological features of Tulipa gumusanica Terzio?lu and its morphologically similar relative, T. armena Boiss. var. armena, in order to clarify their similarities and differences. We found that these taxa have some important differences with regard to anatomical, palynological and ecological features, as well as morphological traits. General anatomical traits of both examined taxa are similar, both having isolateral leaves with distinct hypodermis and a stem with distinct monolayer collenchyma close to the epidermis. However, some anatomical characters such as mesophyll width, average number of stomata on lower epidermis, and epidermal cells on upper epidermis are found to be important in delimiting these taxa. In addition, considerable differences have been observed in pollen shape and size. The species differ ecologically in that T. gumusanica prefers slightly acidic soil with low organic content in the woodland, whereas T. armena var. armena prefers slightly alkali soil with high organic content in steppe vegetation.     

Pollen diversity in the genus Ptilostemon (Asteraceae,Cardueae) from Italy and its taxonomic and palynoecological implications

The results of a study on pollen morphology of the species of the genus Ptilostemon growing in Italy: Ptilostemon niveus, P. greuteri, P. gnaphaloides, P. casabonae, P. strictus, P. stellatus by light and scanning electron microscopy were presented and discussed including in relation to their taxonomic position. The exine shows two different ornamentation patterns: echinae and scabrae. This last ornamentation pattern together with other features was previously described in the genus Ptilostemon. Of 6 species analysed, P. stellatus is the only one that shows a scabrate ornamentation of exine. Two pollen types were recognized through the exine ornamentation, length of ectocolpus and polar outline: P. stellatus type and P. niveus type. A multivariate analysis (principal component analysis and linear discriminant analysis) was carried out with the aim of examining potential morphological characters which could be used to identify taxa. The data suggest that several characteristics can be used to delimit the species in particular the exine ornamentation. The results of our studies support the actually subgeneric classification, and several features of the pollen grains analysed seem to have a palynoecological role and an important taxonomic significance. A dichotomous key based on palynological data is also given.     

A new species of <Emphasis Type="Italic">Baierella</Emphasis> from the Krasnyi Yar locality,Early Cretaceous of western Transbaikalia

Plant remains of Baierella R. Potonié (Ginkgoales) were found for the first time in the Lower Cretaceous deposits of the Khilok Formation (Buryatia Republic), where they form a thin coal bed. A new species, B. averianovii, is described from the Krasnyi Yar locality. The monodominant burial of the new species in combination with pollen grains of Ginkgocycadophytus prevailing in the relevant palynological assemblage allows the authors to reconstruct a monospecific woody wetland plant community.     

Les palynomorphes du Bajocien supérieur : un premier PALYNO-DATA pour les Monts de Rhar Roubane (Algérie nord occidentale)

Apart from the few works carried out in the North Tethyan basins, the palynological study of Mesozoic outcrops is still rare. Thus, the present study devoted to the Zahra Marls Formation (upper Bajocian) of the Rhar Roubane Mountains (northwestern Algeria), allowed us for the first time to inventory 44 different taxa. The palynological assemblages studied are strongly dominated by trilete spores (17 genera and 26 species), the most abundant of which are Concavissimisporites variverrucatus, Cyathidites australis and Cyathidites minor. Pollen grains are relatively frequent (10 genera and 16 species), while acritarchs and algae are represented by only two taxa (Micrhystridium sp. and Botryococcus sp.). In addition, the sporopollinic spectra dominated by the terrestrial elements are represented mainly by the spores of Pteridophyta and Bryophyta and gymnosperm pollen.     

Karyotypic, palynological, and RAPD study on 12 taxa from two subsections of section Idaeobatus in Rubus L. and taxonomic treatment of R. ellipticus, R. pinfaensis, and R. ellipticus var. obcordatus

Twelve taxa belonging to two subsections of section Idaeobatus in Rubus L. from southwestern China were characterized by karyotypic, palynological, and random amplified polymorphic DNA (RAPD) data as follows: (1) The 12 taxa were all diploid species (2n = 2x = 14), among which the chromosome counts for R. mesogaeus var. oxycomus, R. subtibetanus, R. ellipticus var. obcordatus, R. inopertus var. echinocalyx, and R. stans were reported for the first time; (2) All taxa except for R. ellipticus and R. pinfaensis could be distinguished from each other by karyotype, pollen morphology, and RAPD markers. Karyotypes were mainly characterized by the difference in numbers and positions of submetacentric chromosomes and chromosomes with satellited pair, the index of the karyotypic asymmetry, and the ratio of the longest to the shortest chromosome. Pollen morphology were mainly characterized by the discrepancy in specific pollen size, P/E ratio, colpi width, distance between the apices of two ectocolpi, and exine ornamentation characters. The cluster results based on RAPD markers were consistent with morphology classification except for R. pinfaensis; (3) Based on the general data of karyotypic, palynological, and RAPD, R. ellipticus var. obcordatus should be treated as a species R. obcordatus, R. ellipticus and R. pinfaensis should be combined as R. ellipticus, and it was more reasonable to place the combinants and R. obcordatus into subsection Stimulantes rather than into subsection Pungentes.