Pollen morphology and ultrastructure of the Bennettitales: In situ pollen of Cycadeoidea

The micromorphology and ultrastructure of in situ pollen from Cycadeoidea dacotensis are described from permineralized specimens collected from the Lower Cretaceous of North America. Pollen grains are ovoid and relatively small, averaging 25 μm in length and 12 μm in width. Grains are monosulcate with the exine typically invaginated in apertural regions. Exine ornamentation ranges from punctate to psilate. The exine averages 0.73 μm in thickness and is composed of a light-staining sexine and a dark-staining nexine. The sexine consists of a thin, homogeneous tectum, typically with a well-defined inner boundary, and a thicker granular infratectum. The infratectal granules are relatively uniform in size, however, variation occurs in the arrangement of granules. In some grains, the sexine appears homogeneous because there is little lacunal space between the individual granules. The granular infratectum is in direct contact with the underlying nexine. The nexine is uniform in thickness in both apertural and nonapertural regions, and it lacks lamellae throughout. Pollen morphology and ultrastructure are compared with those of the bennettitalean genus Leguminanthus and the dispersed genus Monosulcites. In addition, the fine structure of Cycadeoidea pollen is compared to that of the gymnosperm groups with which the Bennettitales are regarded to be most closely related, including Gnetales, Pentoxylales, and Eucommiidites-type pollen-producing plants.     

STUDIES OF SEED FERN POLLEN: DEVELOPMENT OF THE EXINE IN MONOLETES (MEDULLOSALES)

Monoletes pollen extracted from the seed fern synangium Dolerotheca sclerotica Baxter illustrate four stages in the development of the sporoderm. In the first stage the grains are up to 100 μm long and possess an apparent homogeneous exine in which there is little differentiation between the nexine and sexine. Numerous nexine lamellae and the initiation of sexine expansion mark stage 2 in exine ontogeny. Further expansion of the sexine continues in the third stage until the ratio between the nexine and sexine is approximately 1:5. The final stage in maturation of the sporoderm shows an expanded alveolate sexine with some of the sporopollenin units broken and disorganized. It is at this stage of development that nexine lamellae are most prominent. The formation of sporoderm layers in the fossil grains is compared with pollen grain development in living cycads (Cycadophyta) and a model proposed to account for the apparent early formation of nexine lamellae in Monoletes. The evolution of exine components in early pollen types is discussed.     

THE ULTRASTRUCTURE OF SAHNIA POLLEN (PENTOXYLALES)

The micromorphology and fine structure of in situ pentoxylalean pollen are described from the holotype of Sahnia laxiphora Drinnan and Chambers 1985 collected from the Lower Cretaceous (Valanginian-Aptian) of Victoria, southeastern Australia. Pollen grains are ovoid, monosulcate, and relatively small, averaging 26 μm in length. Exine ornamentation is psilate. The sporoderm is two-parted with the sexine staining lightly throughout and approximately six times the thickness of the more darkly staining nexine. The exine over the sulcus is typically strongly invaginated, and may or may not include an extremely thin sexine layer. The outer part of the sexine is homogeneous, while the inner part is composed of relatively large granules separated by irregular lacunae of various sizes; lacunae are most pronounced at the sexinenexine interface. Faint lamellae characterize the nexine in both apertural and nonapertural regions. Granular orbicules are often associated with the exine surfaces and also occur appressed to pollen sac walls along with lamellated tapetal membranes. Sporoderm ultrastructure is compared to that of nonsaccate pollen of other groups, and particularly to pollen of Bennettitales, Gnetales, angiosperms, and similar plants, to which the Pentoxylales have been thought to be closely related. Although Sahnia laxiphora pollen is not identical to that of any of these taxa, the strongest similarity is with pollen of Bennettitales.     

A Study on Pollen Morphology and Ultrastructure of Subfamily Castaneoideae (Fagaceae) in China

The present paper describes the pollen morphology of 45 species of the subfamily Castaneoifeae (including genera Castanea, Castanopsis and Lithocarpus) from China. The pollen grains were all examined with light microscope, scanning electron microscope and transmission electron microscope. Pollen grains of the subfamily are prolate, subprolate or perprolate, (14.7-23.1)× (8.4 -18.9) μm in size, 3-colporate, the exine in 2-layered, 0.9-1.9μm thick, indistinctly ornate, striate-rugulose or crass-striate, sexine and nexine almost equal in thickness, the sexine consists of tectum, bacules and endonexine under TEM. On the basis of very similar pollen shape, pollen size, type of aperture and exine structure and also other characteristics of plant morphology of the genera Castanea, Castanopsis and Lithocarpus, the present authors tend to support the opinion that they all fall into the samesubfamily, Castaneoideae.     

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.     

西瓜花粉壁超微结构与花粉ATP酶细胞化学定位

研究了西瓜花粉壁超微结构以及单核花粉液泡化时期ATP酶活性超微细胞化学定位。花粉壁的外壁分为外层和内层 ,外层包括覆盖层、基粒棒和基足层等三层 ,内层只包含一层。外层电子密度相对较小 ,内层电子密度相对较大 ;外层与内层之间有缝隙。ATP酶活性反应产物主要分布在细胞质基质、质体、内质网和花粉内壁中     

西瓜花粉壁超微结构与花粉ATP酶细胞化学定位

研究了西瓜花粉壁超微结构以及单核花粉液泡化时期ATP酶活性超微细胞化学定位。花粉壁的外壁分为外层和内层,外层包括覆盖层、基粒棒和基足层等三层,内层只包含一层。外层电子密度相对较小,内层电子密度相对较大;外层与内层之间有缝隙。ATP酶活性反应产物主要分布在细胞质基质、质体、内质网和花粉内壁中。     

Polymorphism in pollen of Salvia leucantha (Lamiaceae)

LM and SEM study of the pollen from single specimen of Salvia leucantha Cav., gathered from Kumaon mountains in Western Himalaya have shown significant variations in aperture number and type, shape and size of pollen grains, hitherto not reported. Normal pollen is 6-colpate but 4, 5, 7, 8, 9, 10, 11-colpate to spiraperturate also occur to make it a heterogenous assemblage. In shape, pollen varies from oblate, suboblate, oblate-spheroidal, prolatespheroidal to subprolate, whereas, in size it ranges from 15 μm to 40 μm. Furthermore, besides the marked variations in monads, the polymorphism is also expressed in terms of dyads and triads. Exine ornamentation however, does not vary, it being reticulate-retipilate sexine pattern in all the different types under LM and showing double sculpturing under SEM.     

Immunocytochemical localization of the allergenic proteins in the pollen of Cryptomeria japonica

Applying an immunocytochemical method, a localization of the protein Cry j I in the Cryptomeria japonica pollen, which is the major allergen responsible for Japanese cedar pollinosis, is investigated with the monoclonal and polyclonal antibodies produced from the protein. The protein that reacts to the polyclonal antibody localizes on the sexine, nexine, between nexine and intine layers, orbicles, cell wall of a generative cell, Golgi body and Golgi vesicles. The allergenic protein contained in the exine and orbicles of Japanese cedar pollen can diffuse or dissolve easily from there into the mucus covering of the eye and nose, causing a response in less than 1 min after exposure. Since the orbicles have a diameter of about 430 nm, they can pass easily through the pores of most protective masks to reach the sensitive tissues of the patient. The proteins react to the monoclonal antibodies (J1BO1 and J1BO7) and localize on the Golgi body, sexine, nexine and orbicles (but not between the nexine and intine layers), and on the generative cell wall. In the young pollen grain, numerous allergenic protein particles contained in the orbicles and sexine layer, but there is only a small amount of the protein between the nexine and intine layers, since the intine layer is not yet complete at this stage. More will be accumulated there during developmental maturation. The allergenic protein is also found on the tapetal materials remaining in the young anther. Since the materials forming the exine layer and orbicles come from tapetal tissue, it is assumed that some of the allergenic protein is produced in the tapetum and localized in the orbicles and pollen wall during maturation, and that the rest of the allergenic protein is produced in the Golgi body in the mature pollen grain.     

鹅掌楸属植物花粉萌发前后壁的超微结构

观察描述了在电镜下中国鹅掌楸（Ｌｉｒｉｏｄｅｎｄｒｏｎｃｈｉｎｅｎｓｅ）和北美鹅掌楸（Ｌ．ｔｕｌｉｐｉｆｅｒａ）２种植物花粉壁的超微结构及其水合后的变化。（１）成熟花粉壁由６层组成,即外壁３层──外层,中层１和中层２,内壁３层──内壁１,内壁２和内壁３。（２）花粉水合时,在内壁３与质膜之间由Ｐ一粒子（多糖－粒子）和被膜小泡参与形成新层。（３）花粉萌发时,由内壁３的一部分和新层突出萌发孔共同形成花粉管壁。（４）新层于花粉管形成早期分成２层──外染色深的果胶层和内电子透明的胼胝质层。     

Pollen morphology supports the transfer of Wendlandia (Rubiaceae) out of Rondeletieae

Pollen morphology of 27 species, eight subspecies and one variety of Wendlandia was studied using scanning electron microscopy (SEM). Wendlandia pollen are monads, radiosymmetric, small in size, tricolporate (rarely tetracolporate or bicolporate) and spheroidal (rarely subprolate or suboblate) in equatorial view. The compound aperture consists of ectocolpus, mesoporus and endocolpus. In addition, reticulate sexine and granular nexine were observed. The pollen wall ultrastructure of two Wendlandia spp. was examined by transmission electron microscopy (TEM). The exine consists of the tectum, columellae, foot layer and endexine. The endexine is thickened into a costa around the aperture. The intine forms a protruding oncus at the aperture. The palynological characters show a remarkable uniformity among the Wendlandia spp. Differences with Rondeletia, the main genus of tribe Rondeletieae, exist in the exine pattern, the endoaperture and the pollen wall structure. Our observations indicated that the endoaperture type and the structure of the pollen wall of Wendlandia were similar to those of the Gardenieae–Pavetteae–Coffeeae–Octotropideae clade, which provided palynological evidence for a closer relationship of Wendlandia to subfamily Ixoroideae and the transfer of Wendlandia out of Rondeletieae. © 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 128–141.     

Pollen morphology of Microstachys (Euphorbiaceae) with emphasis on neotropical species

Abstract

In Euphorbiaceae tribe Hippomaneae is the pantropical genus Microstachys, comprised by 24 species, mostly from Brazil. Palynological studies with several representatives of the genus are scarce. The purpose of this study was to describe the pollen morphology of Microstachys and find possible differentiating characteristics between its species. Ten species of the genus were analysed, represented by 21 herbarium collections. Their pollen grains were acetolysed, measured and photographed under light microscopy (LM) and scanning electron microscopy (SEM). The analysed species possess pollen in monads, of small to medium size, isopolars, amb distincticly trilobed, oblate-spheroidal, prolate-spheroidal or subprolate, tricolporate with narrow and very long colpi, almost fused at the poles sometimes forming an invagination with tapering ends and margo of the colporus wide to very wide and psilate; endoapertures lalongate to very lalongate with tapering ends, presence of a narrow costae distinct in the endoaperture; exine microreticulate homobrochate, walls with simple columella; at the mesocolpus the sexine separates from the nexine forming cavea; and sexine always thicker than the nexine. Microstachys is a stenopalynous genus, despite its species varying in pollen size, shape and width of the cavea, margo of the colporus, and length of the endoapertures, demonstrating taxonomic value, and indicating a contribution towards future systematic analyses.     

Pollen morphological support for the Catesbaeeae-Chiococceae-Exostema-complex (Rubiaceae)

The pollen morphology of the Catesbaeeae-Chiococceae-Exostema complex as recently treated by Delprete (1966) was examined with LM and SEM. The group is remarkably stenopalynous; typical representatives have medium sized, 3-colpate pollen with a perforate tectum covered with microspines. The inner nexine ornamentation is pronounced and offers more variation than the sexine pattern. A typology of the inside structures is presented based on LM observations and SEM observations of sectioned grains. Orbicules are common and numerous in the Catesbaeeae and Exostema-group; for most genera of the Chiococceae confirmation is needed of orbicule presence. All orbicules observed are relatively large (1-4 μm) and spiny. Pollen and orbicule morphology proved to be a powerful tool to delimit the Catesbaeeae-Chiococceae-Exostema complex. The overall delimitation of the complex is corroborated with our pollen data. The genera Mastixiodendron and Placocarpa, however, can be excluded from the complex based on their pollen morphology. Mastixiodendron has 3-colporate, perforate pollen without microspines and the endocolpi are fused into an endocingulum. Pollen of Placocarpa is reticulate and 3-colporate with perpendicular endocolpi.     

Studies on Pollen Morphology of Taxaceae of China

The present study deals with pollen morphology of 4 genera and l0 species of Taxaceae in gymnosperms. Pollen grains of the family are spheroidal or subspheroidal, 20.8μm in diameter and with laptoma or papilla in the distal face. Exine is two-layered, with sexine equal to nexine in thickness, but sometimes the stratification is indistinct. The surface is scabrous or slightly granular under LM. Coarse verrucae and fine tuberculae on pollen surface are observed under SEM. From thin section, endexine is shown to have lamellate structure, and ectexine is made of verrucate elements. In Amentotaxus argotaenia, some pollen grains show remnant saccate. According to pollen morphology, this family may be divided into two tribes: 1, Pseudotaxeae (including Pseudotaxus only), and 2, Taxeae (including Taxus and Torreya). Owirg to the special feature of pollen grains in Amentotaxus the present author suggests that the genus be separated from Taxaceae and raised to the level of family, Amentotaxaceae.     

POLLEN MORPHOLOGY AND ULTRASTRUCTURE OF THE CABOMBACEAE: CORRELATIONS WITH POLLINATION BIOLOGY

Of all species comprising the two genera of the Cabombaceae, only Brasenia schreberi J. F. Gmel. and Cabomba caroliniana Gray have been critically investigated with regard to their pollination biology. Brasenia schreberi has been shown to be anemophilous, while C. caroliniana has an entomophilous (myophilous) pollination syndrome. In the present paper, a number of pollen and pollen-related characters, including pollen size, shape, quantity, terminal settling velocity, pollen-ovule ratios, and overall exine architecture of B. schreberi and C. caroliniana are evaluated. Pollen from both species is elliptic, monosulcate, and has a tectate-columellate sporoderm with supratectal surface ornamentation. Grains of B. schreberi are small, produced in copious amounts, and settle relatively slowly. Flowers of this species have large pollen-ovule ratios. The exine of B. schreberi pollen is scabrate, relatively thin, has a uniformly thick sexine composed of a two-zoned (homogeneous/granular) tectum and distinct columellae, and a homogeneous nexine. Pollen of C. caroliniana is relatively large, produced in small quantities, and has a rapid terminal settling velocity. Flowers exhibit small pollen-ovule ratios. Exine organization of C. caroliniana pollen is typically two times thicker than that of B. schreberi; ornamentation is striate. Nonapertural sexine regions have a thick tectum and well-defined columellae, with both sexine components traversed by a dense system of channels. The nexine is relatively thin. All of the palynological characters examined correlate well with the anemophilous and entomophilous syndromes of B. schreberi and C. caroliniana, respectively. Moreover, several other parameters of exine ultrastructure from each species exhibit positive correlations with the respective pollination mechanisms, including: tectum thickness, columellae diameter, tectum-nexine ratios, and the consistency, distribution, and total amount of pollenkitt present. Overall exine ultrastructure is also discussed from a historical perspective as well as with respect to its phylogenetic significance.     

Dimorphic exine sculpturing in two distylous species ofDyerophytum (Plumbaginaceae)

Light and SEM observations on the pollen ofDyerophytum africanum andD. indicum have revealed marked differences in exine features. These distylous species also have dimorphic pollen. In the short-styled individuals of both species, the sexine and nexine are of equal thickness, and the clava-like sexinous processes are short without marked projections. In the long-styled individuals, the sexine is thicker than the nexine, the clavae are higher than broad with an apical spinule. Pollen size and apertures are identical in both morphs. — Palynological evidence is presented for relationships betweenDyerophytum andCeratostigma, Plumbago andAegialitis. Moreover, the genusDyerophytum exhibits pollen morphological similarities with some species ofLinum (Linaceae).     

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 AND EVOLUTION IN HEDYOTIS SUBGENUS EDRISIA (RUBIACEAE)

Primarily on the basis of aperture structure, 31 species of Hedyotis subg. Edrisia (Houstonia) are separable into 5 palynological groups. Group 1 is characterized by a simple os circumscribed by varying nexinous thickenings, groups 2–4 combine this os with a crassimarginate one to form a compound os, while group 5 is known only with the crassimarginate os. The first type is considered primitive, the compound os specialized and more advanced, and the third type reduced and highly advanced. Other characteristics of the pollen, including size and shape, aperture number, thickness of sexine and nexine, and reticulum, are discussed in relation to the apertures, and their probable primitive and advanced expressions are outlined. The data agree with the phyletic trends found in the sporophyte on the basis of results from morphology, chromosome number and size, and distribution, and they support and add to an earlier phylogenetic scheme proposed for the subgenus. The evidence from palynology also supports the treatment of Hedyotis and Houstonia as congeneric.     

Pollen Morphology of Cyclobalanopsis and Its Relation to Quercus

The present paper deals with pollen morphology of 19 species belonging to Cyclobalanopsis and of 31 species belonging to Quercus from China. All pollen grains were examined under light microscope and scanning electron microscope, and those of 4 species of Cyclobalanopsis and of 8 species of Quercus were examined under transmission electron microscope. Pollen grains of Cyclobalanopsis are spheroidal or subspheroidal, 25.2(18.9-31.5) ×23.1 (16.8-27.3) μm in size. Mostly 3-colporoidate, rarely 3-colpate or 3-colporate. The exine is 2-layered, 1.1-1.9 μm thick, sexine thicker than nexine, finely granulate under LM, granulate, spinulate, verrucate under SEM. Pollen grains of Cyclobalanopsis and of evergreen members of Quercus are very similar to each other in size, aperture and ornamentation of exine, but there are some differences in pollen grains between Cyclobalanopsis and deciduous members of Quercus. Therefore, Pollenmorphology supports the treatment of Cyclobalanopsis as a subgenus of Querc     

Pollen morphology of the Phyllanthus species occurring in the continental United States

Twelve native United States species have been examined. The pollen grains could be divided into five pollen types based on sexine ornamentation, aperture structure, sexine/nexine ratio and sexine 1/sexine 2 ratio. Within these types it was often possible to distinguish the grains of the different species. Two groups of types have been recognized based on the similarities in ornamentation. One group, consisting of the Phyllanthus amarus type, the P. tenellus type and the P. urinaria type, is characterized by the Tilia structure, whereas the second group of types, comprising the P. caroliniensis type and the P. liebmannianus type are microreticulate. The postulation that different subgenera show different pollen types is true in general, but there is one exception: P. niruri, taxonomically belonging to the subgenus Phyllanthus, has pollen grains of the P. caroliniensis type, a type also comprising species from the subgenus Isoclades.