Developmental stages of the pollen wall and tapetum in some Crocus species

The developmental stages of the pollen wall and tapetum, together with exine morphology were studied in a number of Crocus species, by light and scanning electron microscopy. Gametogenesis was characterized by: 1) development of a thick intine, 2) single mitosis, and 3) terminal amylolysis. The tapetum was of the secretory type. In C. cartwrightianus cv. albus, abnormal sporogenesis and gametogenesis produced vacuolate pollen grains with a reduced-or no intine layer, and rich with starch granules; the tapetum was either of the parietal-or amoeboid type. The exine was echinate and the pollen grains had different types of aperture: furrows, colpi or pores. The ornamentation varied from microreticulate to irregularly perforate. The exine framework was overlaid by a pellicle resistant to chloroform-carbon disulphide, on which a layer of pollenkitt was deposited. The results are discussed from both cytological and evolutionary viewpoints.     

Pollen morphology and ultrastructure of Marathrum schiedeanum (Podostemaceae)

The Podostemaceae, or river-weeds, comprise 46 genera and 270 species of dicots and are the largest family of strictly aquatic angiosperms. Despite the large size, specialized habitats, and enigmatic morphology of the family, relatively little is known about the palynology of Podostemaceae. In the current paper, pollen morphology and ultrastructure of Marathrum schiedeanum are described. Pollen grains are relatively small, spheroidal, and tricolpate to spiraperturate. The exine has a microechinate ornament, a tectate-granular sexine and a relatively thick nexine in non-apertural regions, and a semitectate sexine and thinner nexine in apertural regions. Although aperture variation occurs in the family, this is the first report of the spiral aperture type in Podostemaceae. The spiraperturate condition appears to be derived in river-weeds, as does the granular pollen wall, which represents a reduction of the typical columellae found in eudicots.     

A Comparative study on pollen exine ultrastructure of Nothofagus and the other genera of Fagaceae

The genus Nothofagus is mainly distributed in South America and New Zealand. The present paper describes its pollen exine ultrastructure and compares the exine ultrastructure with that of the other genera of Fagaceae. The pollen grains were examined using ultrathin sectioning technique under transmission electron microscope. The study shows that the pollen exine ultrastructure of Nothofagus differs from that of the other genera of Fagaceae by its exine structure and thickness, type of aperture, and ornamentation. The pollen exine of Nothofagus is thin and possesses granular bacules, regular foot layer and tectum, spinulate ornamentation, and the endexine is usually visible at poral area, and 5～8 colpate. The pollen exine of the other genera of Fagaceae possesses entire bacules, irregular foot layer and tectum, granulate and tuberculate ornamentation, thicker endexine, and is 3-colporate ( 3-colpate or 3-colporoidate). The pollen exine ultrastructure of Nothofagus may belong to primitive type. The pollen exine ultrastructure data support Kuprianova’s opinion that Nothofagus should be separated from Fagaceae and established as a monogenetic family, i.e. Nothofa-gaceae.     

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.     

The ultrastructure of fossil dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia,Russia

The general morphology, surface sculpturing, and exine ultrastructure have been studied in dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia. The pollen grains dominate the palynological assemblage extracted from coal deposits of the Khilok Formation in the Buryat Republic, which also contain ginkgoalean leaves of Baierella averianovii as the only constituent of the assemblage of plant megafossils. The relationship between the pollen grains and ginkgoalean leaves from this autochthonous burial is hypothesised on the basis of taphonomical analysis and palaeobiogeographical data. It is shown that the ectexine of the pollen grains includes a thick solid tectum, a thin granular infratectum and a thin foot layer; the endexine is fine-grained, slightly more electron-dense than the ectexine, and is preserved only in places. The distal aperture is formed by a thinning of the exine. No analogous ultrastructure has been described so far in fossil pollen grains of this morphotype studied ultrastructurally from in situ material. For comparison, we also studied the exine ultrastructure of pollen grains Ginkgo biloba. The fossil pollen is not identical to pollen of extant G. biloba, but shows several significant similarities in the exine ultrastructure, which does not contradict the presumable ginkgoalean affinity of the fossil pollen.     

Pollen morphology,ultrastructure and taphonomy of the Neuradaceae with special reference to Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond.

Pollen morphology and sporoderm ultrastructure of modern Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond. were studied using light (LM) and electron (SEM and TEM) microscopy. Additionally late Holocene pollen of the Grielum-type was studied using LM. Systematic and ecological aspects have been discussed for the family Neuradaceae. The pollen grains of the studied species are characterized by similarities in size, shape, aperture type and differences in exine sculpture (reticulate semitectate exine in Neurada and finely reticulate to foveolate in Grielum) and sporoderm ultrastructure. The cavea in the exine is situated between the ectexine and endexine which are connected near the aperture region only. A combination of the palynological characters of the Neuradaceae (semitectate exine, rather loose columellae, interrupted foot layer, the cavea in the exine) increases the pollen plasticity, allowing considerable changes of the pollen grain volume but still remains insufficient to survive sharp fluctuations in hydration level.     

Pollen morphology and ultrastructure of Australian Monimiaceae ‐ Austromatthaea,Hedycarya, Kibara,Leviera, Steganthera and Tetrasynandra

The pollen morphology and ultrastructure of Austromatthaea elegans, Hedycarya angustifolia, H. loxocarya, Kibara rigidifolia, Leviera acuminata, Steganthera macooraia and Tetrasynandra laxiflora, are described. All are Australian members of the Monimiaceae sensu stricto of the order Laurales, subclass Magnoliidae. Except for Hedycarya angustifolia, which has pollen grains in permanent tetrads, all species have small, globose, apolar, inaperturate pollen. They can be identified under SEM by their surface ornamentation: Austromatthaea has fossulate sculpturing; Hedycarya angustifolia has tetrads with a warty configuration; H. loxocarya has echinate pollen; Kibara has spherical gemmae with nipple‐like projections; Leviera has stellate sculpturing; Steganthera has a verrucose surface with small spherical projections on each verruca, and Tetrasynandra is gemmate with one to several spiny projections on each gemma. The pollen grains of all genera of Australian Monimiaceae sensu stricto, some the results of previous studies, are summarized in tabular form. The exine has no columellae, foot layer or endexine, in contrast to the family Atherospermataceae (syn. subfamily Atherospermatoideae of the Monimiaceae, sensu lato). The most elaborate type of wall structure consists of radial elements ("radial processes") with white line‐centered regions extending from beyond the intine to the tectal region and a two‐layered intine with an outer channelled part (onciform zone). Trends of evolution from this type are discussed and comparisons are made with other Monimiaceae, Lauraceae, Amborellaceae and Trimeniaceae.     

美乐多（Melodorum fruticosum Lour．）花粉形态观察

利用扫描电子显微镜（SEM）和透射电子显微镜（TEM）观察了美乐多（Melodorum fruticosum）的花粉形态特征。美乐多花粉为球形或扁圆形的单粒花粉,外壁纹饰为微褶皱状,有点状凹陷,无任何萌发孔或萌发沟。花粉外壁由外壁外层包括覆盖层（连续）、覆盖下层、基足层（1～3层薄片层结构,偶断裂或扭曲至6～10层）和外壁内层（连续）组成。其中,覆盖下层,其厚度为整个花粉外壁厚度的1／2,为混合型结构,即小柱状和颗粒状同时存在,但以颗粒状为主。花粉内壁分为内壁外层和内壁内层,其厚度逐渐变薄。美乐多的花粉特征（单粒、无萌发孔或沟、覆盖层连续、基足层为薄片层结构、花粉外壁内层薄等）与紫玉盘族其他类群一致。     

Pollen morphology and ultrastructure of selected species from Annonaceae

The morphology and ultrastructure of fresh pollen from nine species, one including two varieties representing seven genera of Annonaceae are described based on observations with scanning and transmission electron microscopy. The pollen grains are elliptic with a single furrow, or disulculate. Some are globose with no visible aperture or any indication of a pole. Ornamentation is smooth, rugulate, echinate or verrucate. The tectum is usually continuous and of the same thickness over the whole grain except for the aperture zone, where the exine elements are very often imperceptible. The infratectum may be granular, or columellae and granules are mixed together. The foot layer consists of continuous or irregularly contorted foliations. The endexine is distinct and thin, and varies slightly in thickness in some species, but is vaguely distinguishable in others. The intine is two-layered and consists of an entexine with many vesicular-fibrillar components with tubular extensions, and a more homogeneous endintine. The controversy around the presence of an endexine in Annonaceae is discussed, but whether its presence is ancestral cannot be determined. Data on fresh pollen are compared with those from similar studies on dried pollen.     

The Apertural Wall in Pollen of Linum grandiflorum

The apertural wall in tricolpate pollen of Linum grandiflorumwas investigated in order to understand its functioning duringdesiccation and rchydration. Whole and sectioned pollen grainswere studied with light or electron microscopy and by cytochemicalmeans. The areas of the apertures were examined in fresh drypollen, in grains moistened on agar gel or removed from compatiblestigmas, and in pollen from mature undehisced anthers The intine was found to consist of an inner ß-glucanlayer and an outer pectic layer. At the apertures the pecticlayer is thickened and overlaid by a ß-glucan layer.The pectinaceous intine stains red with basic fuchsin. The presenceof a third wall layer, the medine, was not confirmed. The aperturalintine thickenings possess considerable imbibitional capacityand at rehydration they appear as swollen lenticular bodies A procedure is described for obtaining intact exine free grains(EFG's) and whole, separated exines of L. grandiflorum. Invariably,the released EFG's consisted of protoplasts encased in the cellulosicintine. In most grains the outer intine remained attached tothe separated exine In L. grandiflorum the outer wall of the aperture expands whilethe protoplast and endintine are still infolded. Apparently,the exintine becomes detached from the endintine during desiccationand re-attaches at rehydration. It is suggested that the transientdetachment controls the influx of water into the vegetativecell Except for morph-specific exine processes no differences instructure of the aperture wall or its functioning at rehydrationwere observed between pin and thrum grains Pollen wallM, apertures, exintine, exine free grains, rehydration, desiccation, Linum grandiflorum     

Development of the exineless pollen wall in Callitriche truncata (Callitrichaceae) and the evolution of underwater pollination

 The Callitrichaceae are a monogeneric family of aquatic angiosperms comprising approximately 50 terrestrial, amphibious, and obligately submersed species. Callitriche is unique in being the only known genus with co-occurring aerial and underwater pollination systems. Mature pollen structure is correlated with growth habit, pollination biology, and phylogeny within the genus. In the present study, development of exineless pollen in the obligately submersed species Callitriche truncata was examined, with particular emphasis on the tetrad stage. Pollen ontogeny occurred rapidly and non-synchronously; tetrads, free microspores, and two-celled pollen grains were identified within the same anthers. Formation of the intine also occurred relatively early, during the tetrad stage. Tetrads were surrounded by a structurally distinct envelope, and its ultrastructure and histochemistry indicate that this callose-like envelope is in a transitional state. Reduction or complete loss of the exine has evolved at least twice in Callitrichaceae, and the new ontogenetic data indicate that exine loss evolves more quickly than the loss of callose. In addition, developmental information on exineless pollen in C. truncata coupled with other palynological data for the exine-bearing terrestrial and amphibious growth forms provide support for the hypothesis that underwater pollination has had a relatively recent origin in the family. Received January 2, 2001 Accepted March 27, 2001     

Pollen Morphology and Ultrastructure of Laurelia,Laureliopsis and Dryadodaphne (Atherospermataceae [Monimiaceae])

Pollen morphology and ultrastructure of Laurelia novae-zelandiae A. Cunn., L. sempervirens (Ruiz et Pavón) Tulasne, Laureliopsis-philippiana (Looser) Schodde and Dryadodaphne trachyphloia Schodde are described. Laurelia, Laureliopsis and Dryadodaphne have medium-sized, isopolar, globose to globose-ellipsoidal pollen which is either dicolpate (Dryadodaphne, rarely in Laureliopsis) or meridionosulcate, with a median encircling aperture with two wider parts centered at the poles (Laurelia, most pollen of Laureliopsis). Exine is tectate-columellate with an uneven foot layer showing irregular discontinuities. A few tangentially-aligned lamellae show some resemblance to an endexine and in some sections there appears to be an intergradation between these lamellae and small tangentially flattened foot layer parts. The intine consists of an outer channelled zone, with radial (Laurelia sempervirens) or tangential (Dryadodaphne) alignment of channels and an inner intine of homogeneous appearance. The outer intine is thicker in apertural regions and the inner intine is thicker within the apertures of Laureliopsis and Dryadodaphne. The pollen grains of 6 of the 7 genera of Atherospermataceae are compared in tabular form. Although pollen grains show links with other Monimiaceae (sensu lato), it is sufficiently distinct to support the existence of the Atherospermataceae as a separate family. It is acknowledged that, on other grounds, a good case can be made for retention of the group as a subfamily within the Monimiaceae.     

Pollen wall development in Vigna vexillata I. Characterization of wall layers

Light and electron microscope observations characterized the layers that comprise Vigna vexillata L. pollen walls, and identified the timing of their development. Exine sculpturings form an unusually coarse ektexinous reticulum. The structure of the ektexine is granular; this differs from the columellate/tectate type of structure typical of most angiosperm pollen. The ektexine overlies a homogeneous-to-lamellar, electron-dense endexine, which in turn surrounds a thick, microfibrillar intine. Pollen grains are triporate and operculate, with Zwischenkörper and thickened intine underlying the apertures. The ektexine forms during the tetrad period of microspore development, the endexine and Zwischenkörper during the free microspore stage, and the intine during the bicelled (pollen) stage. Coarsely reticulate exine sculpturings and the granular structure of the patterned exine wall of the pollen grains are features that make this species suitable for detailed studies of pollen wall pattern formation.     

COMPARATIVE POLLEN MORPHOLOGY AND TAXONOMIC AFFINITIES IN CYCADALES

Scanning and transmission electron microscopy of pollen grains of 29 species, representing the ten extant genera of Cycadales, has provided valuable insight into their relationships. Pollen grains of these taxa are boat-shaped, monosulcate, and bilaterally symmetrical. They range from narrowly to widely elliptical or subcircular when viewed distally, and have an exine surface of psilate, foveolate, or fossulate. Pollen wall ultrastructure of Cycadales is typically tectate with alveolate∗∗∗spongy exine. The nexine is laminated in all genera. Nexine 1 (footlayer) is present in most species as a thin and often discontinuous layer. There is consistent variation in thickness of the sporoderm layers among the genera but relative uniformity within them. Pollen characteristics are well correlated with macro- and micromorphological features, chromosome numbers, geographical distribution, and postulated pollination mode. A close affinity between Encephalartos, Lepidozamia, and Macrozamia is recognized. Pollen characteristics of the genus Bowenia show some similarity with those of the latter group. Except for two species of Macrozamia which are narrowly elliptic, all of the genera have widely elliptic pollen and share a psilate exine surface and the thinnest sexine with nearly identical arrangement of alveoli. Pollen grains of the species in the genus Dioon exhibit a unique morphology but are more similar to Stangeria than they are to those of taxa in Zamiaceae. The circular outline of the grains and the foveolate exine surface are characters shared by these two genera, but several morphological features distinguish Dioon from Stangeria. Ceratozamia and Zamia share a widely elliptic shape, foveolate exine surface and nearly identical sexine, as well as morphological features and chromosome numbers. They differ from Microcycas in sexine thickness, gross morphology and chromosome numbers. The pollen grains of Cycas circinalis and C. revoluta differ in size and structure of the sexine from all other genera and from each other, substantiating their distinct subgeneric delimitations.     

Pollen Morphology of the Periplocaceae from Madagascar

The pollen morphology of eleven (Baroniella Constantin & Galland, Baseonema Schltr. & Rendle, Camptocarpus Decne., Cryptolepis R. Br., Cryptostegia R. Br., Gonocrypta Baill., Harpanema Decne., Ischnolepis Jum. & H. Perrier, Menabea Baill., Pentopetia Decne., and Tanulepis Balf. f.) of the 13 genera of the Periplocaceae from Madagascar have been examined using light-, scanning-, and transmission electron microscopy. All of the genera are characterized by pollen grains arranged in tetrads. The arrangement of the grains may be rhomboidal, decussate or tetragonal. The 4–6 pores present are restricted to the junction area of adjacent grains. Cryptostegia differs from the other genera in that the arrangement of pollen grains is only decussate. In Menabea the tetrads are united into a pollinium. The exine is smooth and consists of a distal stratum (tectum), subtended by a granular stratum consisting of granules of unequal size. Towards the base larger granules are present. In Camptocarpus, Harpanema and Tanulepis the exine is stratified into a distal stratum (tectum), a thin granular stratum and an almost continuous basal stratum (foot layer). The inline is well developed. The pollen grains of tetrads are connected by wall bridges (cross-wall cohesion). The internal walls in Camptocarpus, Harpanema and Tanulepis differ from the other genera in the absence of a tectum. The pollen morphology of the taxa investigated is very similar and of little value for distinguishing the species and genera investigated. The distinctive difference in exine structure between the above mentioned three genera and other genera investigated emphasizes the importance of exine ultrastructure in the Periplocaceae.     

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.     

Studies on pollen morphology of selected species of Annonaceae from Thailand

The pollen morphology of 49 species and one variety, representing 18 genera of the family Annonaceae from Thailand, is described and illustrated based on observations using scanning electron microscopy (SEM). The pollen grains of Anaxagorea show double-spheres as a result of the intine extrusion. The palynological evidence confirms the close relationship of Dasymaschalon, Desmos and Asian Friesodielsia. Decussate tetrads in Goniothalamus and coexisting tetragonal, rhomboidal, T-shaped, tetrahedral and decussate tetrads in Mitrephora are reported. Pollen morphology is consistent within Huberantha, Marsypopetalum and Monoon, but is more diverse in Polyalthia sensu stricto Pollen unit, shape, size, ornamentation and aperture number reaffirm the great diversity among and within genera in Annonaceae.     

Polarity, aperture condition and germination in pollen grains ofEphedra (Gnetales)

Pollen grain polarity, aperture condition and pollen tube formation were examined inEphedra americana, E. foliata, E. rupestris, E. distachya, andE. fragilis using LM, SEM and TEM. In the characteristic oblate pollen, as seen in situ in the tetrad configuration, the polar axis is the minor one and the equatorial plane runs between the two narrow ends of the microspore. The intine is thick in fresh fixed mature pollen but we have seen no indication of regions having an exceptionally thick intine that could be considered associated with an aperture or apertures. About three minutes after transferring fresh pollen to the germinating medium the ridged exine splits and twists away from the intine and its enclosed protoplast. The shed exine spreads out and curls into a scroll-like configuration that is as distinctive as that of the pollen shape had been but now having the ridges and valleys perpendicular to the long axis. The pollen tube develops, in our experience with more than a hundred germinating pollen grains, near one of the narrow tips of the pollen grain's equatorial plane. The location of the pollen tube initiation probably is related to the position of the tube cell nucleus. The pollen tube starts to grow about one hour after the exine was shed. The pollen tube emerges close to the narrow end (equator) of the gametophyte. This end emerged first as the exine is shed and is opposite to the prothallial cells. The stout pollen tube is c. 10µm in diameter grown in vitro on agar. In our germination medium the stout tube continued to elongate for about 24 hours reaching a length of c. 100 µm. With respect to exine morphology the aperture condition could be considered as inaperturate. The pollen tube, however, is formed in a germination area near one end of the exineless gametophyte.     

Pollen Morphology of the Family Zingiberaceae in China—Pollen Types and Their Significance in the Taxonomy

Pollen morphology of 89 species and 3 varieties belonging to 18 genera (out of 150 spcies in 20 genera) of Zingiberaceae in China was studied under both light microscope and scanning electron microscope. Pollen grains of Zingiberaceae are spherical, subspherical, ovoid and prolate, 36-225 μm in size, nonaperturate or aperturate (spiraperturate, porate). Pollen grains are almost not resistant to acetolysis. The wall is composed of a very thin exine and a thick intine. The exine is psilate, spinate, cerebelloid-areolate, striate, verrucate and foveolate. According to the presence or the absence of aperture and differential ornamentations, two types and six subtypes are recognized: I. The type Nonaperturate: (85 species and 3 varieties in 18 genera). Four subtypes can be recognized within the type based on the characteristics of the exine sculpture. These are: (1) The subtype Psilate, in which, the exine is nearly smooth (including: Hedychium, Curcuma, Kaempferia, Caulokaempferia coenobilis, Boesenbergia rotunda, Stahlianthus, Amomum compactum, Etingera, Hornstedtis, Rhynchanthus). (2) The subtype Spinate, which comprises two groups: (A) The group Short-spinate, pollen grains with smaller spines (Globba), (B) The group Long-spinate, pollen grains with longer spines (Alpinia, Amomum, Plagiostachys, Roscoea, Cautleya, Boesenbergia fallax, Caulokaempferia yunnanensis). (3) The subtype Cereblloid-areolate, pollen grains of which are spherical or subspherical, with cerebelloid sculpture (Zingiber Sect. Zingiber). (4) The subtype Striate, pollen grains of which are prolate or oliveshaped, and striate (Zingiber Setc. Cryptanthium). II. The type Aperturate, in which pollen grains are acetilysis-resistant and possess distinct apertures (mixed colpate-porate or forate), including two subtypes: (1)The subtype Mixed colpate and Porate. Pollen grains are both 3-colpate and 1-3-porate, and usually with one long spiral, two short (straight or slightly curved) colpi and 1-3-poris. The exine is verrucate or not, nearly sinuolate (Costus speciosus, C. tonkinensis, C. lacerus). (2) The subtype porate, whose grains are 6-8-porate and exine is foveolate (Costus megalobractea). The taxonomic significance of the pollen types in the family Zingiberaceae is also discussed.