Unique tetrads of <Emphasis Type="Italic">Epilobium luteum</Emphasis> (Onagraceae: Onagreae) pollen from Alaska

Aperture morphology of tetrad pollen of Epilobium luteum (Onagraceae: Epilobieae) from three Alaskan collections is highly variable. The first collection appears to lack apertures altogether and is presumed to consist of immature pollen gains in a genus known to achieve mature size before the apertures become distinctly protruding. A second collection has tetrads with 3- and 4-apertured grains, the apertures in the latter are often irregularly spaced and not in apposition with the apertures of neighboring members. The third collection consists of the more typical 3-apertured members that characterize the majority of Epilobium pollen grains. In all of these collections individual pollen grains (monads) are interspersed among the tetrads. The variations in the number of apertures emphasize the importance of having a comprehensive understanding of the stage of development of the pollen (taxon) examined when describing pollen collections. In the first collection this would mean the recognition that in Onagraceae apertures occur in the later stages of microspore ontogeny. In the latter two collections a thorough background of the literature of the pollen morphology on this largest Onagraceae taxon is useful for the understanding of the significance of a range of aperture numbers on Epilobium pollen grains.     

A survey of species assigned to the fossil pollen genus Anacolosidites

Anacolosidites Cookson & Pike, a fossil pollen genus recorded since the Campanian, is peculiar in its morphology – six‐porate with three apertures on each hemisphere, located away from the equator, and with the distal and proximal apertures positioned over each other. Representatives of this fossil genus are widely considered to represent extant Olacaceae from tribe Anacoloseae. Olacaceae is an exclusively tropical angiosperm family with a pantropical distribution; consequently the fossils are often used to suggest a tropical climate and in addition are frequently used as a stratigraphic marker. Fossil species assigned to Anacolosidites are quite variable and may not all represent Olacaceae, in which case they may not indicate tropical climate.

The present study is a morphological survey of fossil pollen assigned to Anacolosidites; it identifies the published reports of the fossil species that probably represent positive occurrences of Olacaceae pollen in the fossil record. Within Olacaceae, Anacolosidites‐type pollen is usually compared with pollen of genera in tribe Anacoloseae, in particular: Cathedra, Anacolosa and Phanerodiscus, but never with the pollen of Ptychopetalum, a genus from tribe Olaceae with closely similar pollen to the other three genera, but with a reticulate tectum and very small circular apertures located near the equator. Nevertheless, the records of reticulate Anacolosidites species which have been excluded from the emended diagnosis are unlikely to be related to Ptychopetalum. The earliest accepted record of Anacolosidites is from the Late Cretaceous (Maastrichtian) of Germany. However, most Late Cretaceous records, and later Russian and Chinese occurrences referred to Anacolosidites, consist mainly of Normapolles‐type pollen, whereas many of the Cenozoic records assigned to Anacolosidites have a much clearer affinity with the pollen of Anacolosa, Cathedra and Phanerodiscus (tribe Anacoloseae). The newly emended genus Anacolosidites may be used as a stratigraphic marker for tropical or megathermal climatic conditions.     

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.     

Multiple origins of a unique pollen feature: stellate pore ornamentation in Amaranthaceae

Stellate pore ornamentation is an unusual feature of angiosperm pollen, so far it is known in only ten genera of Amaranthaceae. The pollen grains of these plants have apertures with large hook‐shaped ektexinous bodies that are stellately arranged. Previous studies interpreted this character complex as a synapomorphy in consideration of its strong specialization. By reconstructing the evolution of stellate pore ornamentation based on phylogenetic trees of Amaranthaceae obtained by parsimony, likelihood, and Bayesian analysis of chloroplast trnK/matK DNA sequences, clear evidence is provided for several independent origins and reversals to less specialized aperture types. In addition to the gomphrenoid genus Pseudoplantago, stellate pore ornamentation evolved several times among achyranthoid genera, which have an African distribution. The most derived apertures, with 5 – 6 large protruding hooks, appear independently in Centemopsis on the one hand, and in Psilotrichum sericeum on the other. In an effort to break down the complex character syndrome of stellate pore ornamentation, we delimited a set of six pollen morphological characters that could be independently traced on the phylogeny. It appears that stellate pore ornamentation was independently derived from apertures with equally spread ektexinous bodies that became hook‐shaped, reduced in number, and symmetrically arranged. Likewise the symmetrically arranged, rectangular ektexinous bodies in Marcelliopsis represent an independent specialization. In view of this pattern of morphological changes, functional significance in the context of specialized insect pollination syndromes and positive selection for stellate pore ornamentation is hypothesized. Stellate pore ornamentation provides an example of a specialized pollen character complex with adaptive significance, and underlines the need for a dense taxon sampling for analyses of character evolution.     

Triporate pollen in the Arecaceae

Triapertury is rare in monocotyledons. The well-defined, regularly spaced, circular porate apertures that occur in Arecaceae: Areca klingkangensis from Borneo, and species of the West African genus Sclerosperma, appear to be unique in monocotyledons. There is evidence to suggest that tripory in Arecaceae has been derived from trichotomosulcy, although in Areca equatorial zonosulcy may have an important role. The apical triporate, and zonosulcate pollen of Areca are described, as well as examples of mono- and trichotomosulcate pollen within the genus. The sub-apical distal triporate pollen of Sclerosperma gilletii and S. mannii are described. Notably, in Sclerosperma pollen, aperture position at post-meiotic tetrad stage follows the rare ‘Garside's rule’ (four groups of three apertures), previously only demonstrated for Proteaceae and Olacaceae. Possible reasons for the occurrence of these rare triporate pollen phenomena in palms are considered. The bearing this may have on the transition from the distal polar position of the single sulcus, to the radial symmetry of the triaperturate condition in many dicotyledons is discussed in comparison with other examples of triapertury in monocotyledons.     

A PALYNOLOGICAL INVESTIGATION OF THE GENUS TOURNEFORTIA (BORAGINACEAE)

The pollen morphology of 65 species of Tournefortia L. was examined by light, scanning, and transmission electron microscopy. Four distinct morphological types were found: Type I, grains subprolate with 3-colporate apertures alternating with three pseudocolpi and the ektexine psilate; Type II, grains subprolate, the poles expanded, 3-colporate with the ektexine psilate polarly and verrucate equatorially; Type III, grains spheroidal with three porate apertures and the ektexine clavate; Type IV, grains suboblate with 3–4 colporate apertures and the ektexine psilate to finely rugose. Type I was found in 46 species representing the most diverse group of tournefortias. Type II was found in 12 species from the Old and New Worlds representing two related groups. Type III was found in five closely related species from the American tropics. Type IV was found in two species from South America, but differences in both the pollen and sporophyte indicate that this grouping may be artificial. Pollen morphology does not support the separation of those species treated as Messerschmidia and confirms the close relationship of Tournefortia and Heliotropium. The striking morphological divergence of Tournefortia pollen raises the question of its adaptive significance.     

Triaperturate pollen in the monocotyledons: configurations and conjectures

Triaperturate pollen are known in at least twenty seven genera of monocotyledons. Differences between aperture type and polarity indicate that the development of three apertures has occurred a number of times. Mode of cytokinesis during microsporogenesis is compared with differences in aperture configuration, to assess the extent to which this appears to influence aperture arrangement. Triapertury in monocot pollen tends to fall into one or another of three situations: 1) it is the normal state, 2) it is fairly common, but pollen with more or less apertures also occur in the taxon or sample, 3) it is a rare, or abnormal state for pollen which usually has less than three apertures. The various forms of triaperturate pollen are described, as well as monosulcate pollen of the orchid genera Cypripedium and Paphiopedilum, often misinterpreted as tri-sulcate, and the unusual extended trichotomosulcate pollen of Agrostocrinum (Hemerocallidaceae). Monosulcy, trichotomosulcy, and zonasulcy, with unusual and rare exceptions of zonasulcy in the eudicots, are aperture states shared exclusively with the basal dicots. Furthermore, to some extent all have links with the triaperturate condition in monocots and basal dicotyledons. This is discussed, as well as the association of tripory with polypory in monocots and basal dicots. The fossil pollen record is considered.This paper is dedicated to Klaus Kubitzki in recognition, not only for his extensive contribution to systematic botany, but also for his firm belief that pollen characteristics contribute to a better understanding of plant systematics and evolution.     

Release of proteins from the pollen wall of Linum grandiflorum

Summary The emission of proteins from the pollen wall of Linum grandiflorum stained with Coomassie blue was followed directly in moistened grains as well as in pollen prints. Within the first minute of the grain being moistened exine-borne proteins emerged from both inter-apertural and apertural sites; subsequently, proteins of a different nature were discharged from the apertures only. In a fraction of the grains the release of intine proteins was not preceded by that of exine proteins. Pin and thrum pollen did not differ in terms of mode or site of this protein emission. The presence and emergence of exine proteins from the apertures is explained by the process of infolding of the colpal wall at desiccation and its expansion at rehydration, which causes an initial trapping and subsequent re-exposure of surface materials. This explanation may also account for the occurrence of poral sporophytic proteins in the pollens of many dictoyledons.     

THE POLLEN WALL OF CANNA AND ITS SIMILARITY TO THE GERMINAL APERTURES OF OTHER POLLEN

The pollen wall of Canna generalis Bailey is exceptionally thick, but only a minor part of it contains detectable amounts of sporopollenin. The sporopollenin is in isolated spinules at the exine surface and in the intine near the plasma membrane. There is no sporopollenin in the > 10 μ thick channeled region between spinules and intine. We suggest that the entire pollen wall of C. generalis is similar to the thick intine and thin exine typical for germinal apertures in many pollen grain types. Considered functionally, the Canna pollen wall may offer an infinite number of sites for pollen tube initiation and would differ significantly from grains that are inaperturate in the sense of an exine lacking definite germinal apertures.     

Aperture variation in the pollen of Nelumbo (Nelumbonaceae)

The evolutionary and developmental origin of tricolpate pollen is of great interest because pollen of this kind defines a major clade of angiosperms (eudicots), a clade that is also well supported by molecular data. We examined evidence that tricolpate and monosulcate pollen types are produced alongside each other in the anthers of Nelumbo flowers, as has previously been reported. Observations of pollen in situ within individual anthers revealed mainly tricolpate pollen produced in tetrahedral tetrads, but also a small percentage of clearly aberrant pollen grains that have a great variety of aperture configurations. Previously published evidence for tetragonal tetrads is not supported, and previously reported monosulcate grains are part of a continuum of variation among the aberrant grains in aperture number, position and form. Other eudicots show similar variability in their pollen apertures. The variation in the pollen of Nelumbo is not exceptional, and may not be more significant than variation seen in the other taxa with regard to the origin of the tricolpate and tricolpate‐derived pollen characteristic of eudicots. Nevertheless further studies of aberrant pollen in Nelumbo and other eudicots, together with comparisons of pollen development in “normal” eudicots and closely related species that show radical, and developmentally fixed, reorganization of apertures and pollen polarity, may be helpful in understanding the processes that controlled the transition from the monosulcate to the tricolpate condition.     

Pollen–pistil interaction in protogyny and self-incompatibility system of Indian mustard (Brassica juncea (L.) Coss.)

The pollen morphology of two species of Drosera has been investigated by means of both light and electron microscopy. The apertures are situated proximally, a state rarely found in the pollen of Angiospermous plants. The pollen morphology of Aldrovanda, Dionea and Drosophyllum is compared.     

The Pollen of Swedish Callitriche (Callitrichaceae) - Trends Towards Submergence

The pollen morphology of the six Swedish Callitriche L. species was investigated using LM, SEM and TEM. The surface ornamentation is reticulate in C. stagnalis, C. platycarpa, C. cophocarpa and C. palustris with supratectal elements in the first three species. The ectexine is reduced in C. hamulata, occurring as scattered granules, but completely absent in C. hermaphroditica. None of the species has distinct apertures but C. cophocarpa and C. platycarpa both have leptomata. The ultrastructure of the pollen wall in C. palustris shows regions with lamellated footlayer and an endexine which may function as apertures. Pollen morphology is found to be related to pollination biology; species with leptomata sometimes being pollinated through ephydrophily and species with reduced exine being hyphydrophilous.     

Why does some pollen lack apertures? A review of inaperturate pollen in eudicots

Apertures are key characters of pollen grains with systematic importance in angiosperms. They function as sites for pollen tube exit, water uptake, transfer of recognition substances and accommodation of volume changes. Not all pollen has apertures; inaperturate pollen (lacking obvious apertures) characterizes many angiosperm groups, especially in early divergent angiosperms and monocots, but also eudicots. In order to expand our knowledge of the systematic distribution, possible functional significance and development of inaperturate pollen in angiosperms, this review focuses on inaperturate and cryptoaperturate (with hidden apertures) pollen in the large eudicot clade, which comprises about 75% of present‐day angiosperm species. It includes new TEM observations of inaperturate pollen from four exemplar taxa selected from different parts of the eudicot phylogeny. Two categories of inaperturate (including cryptoaperturate) pollen occur in eudicots. (1) Sterile attractant or feeding pollen associated with functional dioecy has evolved iteratively at least six times in conjunction with complex breeding systems in the core eudicots. (2) Fertile pollen has evolved numerous times independently throughout eudicots, though generally in a relatively small number of individual taxa. Notable exceptions are the petaliferous crotonoid Euphorbiaceae s.s., in which fertile inaperturate pollen occurs in c. 1500 species, and two subfamilies of Apocynaceae s.l. (Secamonoideae and Asclepiadoideae) with c. 2500 species with fertile inaperturate pollen in pollinia. Fertile inaperturate pollen is sometimes (but not always) associated with an aquatic habit, parasitism, insectivory, heterostyly, anemophily or pollinia. Most fertile inaperturate pollen has a thin exine, or the exine is largely restricted to isolated components (muri, protuberances, subunits) separated by thinner areas which probably function as apertures. In cryptoaperturate pollen, the aperture is covered by continuous exine which probably has a protective function, similar to an operculum. Developmentally, inaperturate pollen is not associated with any particular tetrad type or meiotic spindle orientation (unlike some apertures) due to the absence of a colpal shield of endoplasmic reticulum or other organelles and hence is independent of microsporogenesis type. The lack of a colpal shield during the tetrad stage of development permits complete deposition of first primexine and then exine around each microspore, possibly mediated by the action of the DEX1 protein. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 155 , 29–48.     

Erratum

It is confirmed for Piptocalyx moorei Oliver of the Lauralean family Trimeniaceae, from an examination of the shape of immature pollen at the tetrad stage and soon afterwards, that its biaperturate pollen is of the disulculate type. Two elongated apertures are latitudinally aligned at the equator of each grain.     

Studies in Montia L. and Claytonia L. and Allied Genera

The pollen morphology of several genera in Portulacaceae is described. Particular attention has been paid to the genera of the subfamily Montioideae, as a stage of continued monographical studies. Among genera especially dealt with are Claytonia, Montia, Crunocallis, Naiocrene, Neopaxia, Mona, Maxia, Limnalsine, and Montiastrum. In the taxonomical treatment of these genera the pollen morphology has proved to afford many important additional characters.

The pollen grains of Claytonia are distinguished from those of the remainder in being 3-colpate. The grains of the Claytonia-type have many similarities with those of Lewisia, a genus of the subfamily Portulacoideae. The other genera of Montioideae have pantocolpate pollen grains. Among these genera several different pollen types are distinguished, chiefly with regard to the sexine structures and the aperture membranes. The Montiastrum-type is especially interesting, with tholate grains, a particular pollen type not met with in any other genus in the family. The pollen morphology of some genera in the Portulacoideae is also treated. In some species in Calandrina and Talinum pantotreme pollen grains are observed with apertures transitional between pori and colpi. The apertures of the pantotreme grains are arranged in characteristic patterns.

Particular attention has been given to the variation of the pollen morphological characters. This variation has been examined with regard to the differences between different populations of the same species as well as between different species. The greatest variation has been observed in the shape and size of the grains. The structure and sculpture and thickness of the sexine and the aperture membranes are less variable. Some polyploid taxa are connected with the occurrence of pollen grains with divergent and varying aperture numbers.

In a survey of the genera the taxonomical results of the investigation are presented with particular regard to the pollen morphology. The new genus, Maxia Ö. Nilss., is described. One new species, Montia clara Ö. Nilss., is described and some new combinations are made.

Pollen morphological diagnoses are given for 46 different taxa. The aperture conditions for 96 different species are presented.     

Pollen morphology of Astragalus section Hymenostegis (Fabaceae) and evaluation of its systematic implications

Astragalus is with nearly 3000 described species the largest genus of flowering plants. So far analyses of pollen characters have only been conducted for a few species of the groups within the genus. Here we analyse pollen grains of 22 species representative for Astragalus section Hymenostegis using scanning electron microscopy. We found the basic shape of the pollen grains to be oblate-spheroidal and apertures to be tricolpate as for other eudicots. The sculpturing pattern of the exine is micro-reticulate. Pollen grains show low morphological variation among different species of this section, but differences occur between sections of the genus. We conclude that the vast morphological differentiation that occurred during the rapid radiation of section Hymenostegis was not accompanied by comparable differentiation in pollen morphology.     

Light and electron microscopies reveal unknown details of the pollen grain structure and physiology from Brazilian Cerrado species

Pollen grains have a relatively simple structure and microscopic size, with two or three cells surrounded by the protective sporoderm at maturity. The viability and efficiency of pollen transport from anther to stigma depends on pollen physiological properties, especially the relative water content of the vegetative cell. Pollen transport is a crucial fate for most angiosperms that depends on biotic pollinators and studies focusing on understanding the morpho-physiological properties of pollen grains are still scarce, especially to tropical open physiognomies as the Brazilian Cerrado. Therefore, we investigate some structural and physiological aspects of pollen grains from six native species naturally growing in one Cerrado area: Campomanesia pubescens (Myrtaceae), Caryocar brasiliense (Caryocaraceae), Erythroxylum campestre (Erythroxylaceae), Lippia lupulina (Verbenaceae), Pyrostegia venusta (Bignoniaceae), and Xylopia aromatica (Annonaceae). We selected dehiscent anthers and mature pollen grains to analyze (1) the anther wall and pollen microstructure, (2) the pollen water status at the time of anther dehiscence, and (3) the pollen chemical compounds. In all analyzed species, the anther and pollen developed in a successfully way, and except for Caryocar brasiliense, all species were able to emit pollen tubes in the germination tests. As expected for a dry and open environment, most species dispersed their pollen grains in a partially dehydrated form, as indicated by our harmomegathy experiment. As indicated by our study, the pollen ability in preventing dissection, maintaining its viability in a dry and hot environment during its transport from anther to stigma, may be related to the sporoderm apertures and to the reserve compounds, mainly carbohydrates in the form of hydrolysable starch grains.

     

Using palynomorphological characteristics for the identification of species of Alsinoideae (Caryophyllaceae): a systematic approach

Palynological characters of 18 species belonging to seven genera of the traditional subfamily Alsinoideae including Arenaria, Cerastium, Eremogone, Lepyrodiclis, Minuartia, Sabulina and Stellaria were studied in detail using light and scanning electron microscopy. Pollen grains of subfamily Alsinoideae are subspheroidal or prolate, pantoporate and 20.04 to 51.4 µm in size, prominent and sunken apertures uniformly distributed on the pollen surface. Two types of pollen grain ornamentation were observed, i.e. microechinate-punctate or microechinate-perforate. Echini are present on the surface of the pollen of all investigated species with medium, dense, or sparse echinodensity. These species exhibit variation in polar view, equatorial diameter, number of apertures, exine thickness, diameter of pore, appendages per pore, pore ornamentation, echini arrangement, echinidensity and shape of pollen. Based on qualitative characters, a dichotomous key has been developed for quick and easy identification. The present investigation contributes to the systematic approach using palynological characteristics and correct identification of species for members of subfamily Alsinoideae (Caryophyllaceae).     

Evolution of pollen,stigmas and ovule numbers at the caesalpinioid–mimosoid interface (Fabaceae)

In this study we examine the pollen, stigmas and ovaries from 62 collections of herbarium material representing 16 genera, using light and scanning electron microscopy. The caesalpinioid Dimorphandra group (Burkea, Dimorphandra, Erythrophleum, Mora, Pachyelasma, Stachyothyrsus and Sympetalandra) pollen grains are small, tricolporate monads, with perforate or psilate ornamentation. Dinizia, Pentaclethra and Aubrevillea have morphological characters that have suggested either a mimosoid or caesalpinioid placement. Dinizia pollen is in permanent tetrads with clavate ornamentation. Pentaclethra pollen grains are monads, two species have tricolporate pollen and the third is porate. Aubrevillea has tricolporate, finely reticulate monads. All ten genera have variable, non‐predictable stigma type and ovule number. The mimosoid Adenanthera group (Adenanthera, Tetrapleura, Amblygonocarpus, Pseudoprosopis, Calpocalyx and Xylia) pollen grains are in 8‐ to 16‐grain polyads. In all Adenanthera group species, the stigmatic cavity is only large enough to accommodate one polyad. In addition, the number of ovules present matches the number of pollen units in one polyad. Polyads have porate, operculate apertures that differ in layout, aperture morphology and development when compared with caesalpinioid and other eudicot pollen. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 162 , 594–615.     

An Ultrastructural Study of Pollen Grains Consumed by Larvae of Osmia Bees (Hymenoptera,Megachilidae)

Pollen samples from provisions and faeces found in the nests of four Osmia species were analyzed by SEM and TEM. The pollen grains studied were Cistus, Sonchus type oleraceus. Primus type dulcis, and Quercus type ilex. The apertures of Cistus and Sonchus pollen stored in the provisions were slightly expanded, and the cytoplasm protruded through them. Conversely, Prunus and Quercus pollen grains showed hardly any signs of such apertural protrusions. Further, the cytoplasm of Cistus and Sonchus pollen (which have thin intines) was almost entirely lacking in the pollen grains recovered from faeces, while in the faecal pollen grains of Prunus and Quercus (with thick intines) the cytoplasm was much less modified. These preliminary results indicate that both the protrusion of the cytoplasm in the provisions and the thickness of the intine may play an important role in the digestion of pollen grains by Osmia bee larvae.