Erdtmanitheca portucalensis,a new pollen organ from the Early Cretaceous (Aptian–Albian) of Portugal with Eucommiidites-type pollen

A new lignitised, slightly compressed pollen organ, Erdtmanitheca portucalensis, with affinities to extinct Erdtmanithecales from the Early Cretaceous (Aptian–Albian) of Vale de Água (Lusitanian Basin, western Portugal), is described. The pollen organ is composed of loosely arranged microsporophylls radiating from a central core. The estimated number of microsporophylls is about 100–150. The microsporophylls are sessile and ellipsoidal to barrel-shaped with a flattened or slightly apically depression containing about ten narrow sporangia. The sporangia enclose abundant well-preserved pollen grains of Eucommiidites-type. Pollen grains found in situ are elliptical in equatorial outline, about 16.0–27.2 μm long and 11.9–16.4 μm wide. The main (distal) colpus is long with expanded rounded ends. It is flanked by two subsidiary colpi in an almost equatorial position. The surface of the pollen wall is psilate and occasionally punctate. The ektexine is composed of a distinct tectum, granular infratectal layer and a thin foot layer. The endexine is thick and laminar. The new Early Cretaceous Portuguese pollen-organ is similar in several respects to that of Erdtmanitheca texensis described from the Late Cretaceous of Texas, USA. The new fossil species further documents the importance of the Bennettitales-Erdtmanithecales-Gnetales group in the Early Cretaceous floras of Portugal extending the stratigraphic and geographical distribution of the genus with regard to systematic and phylogenetic significance of the Eucommiidites-producing plants that may have been co-occurring with the Early Cretaceous diversification of angiosperms. It is ascertained that perforate tectum occurs in pollen grains with a well-developed foot layer as well as in pollen grains in which a foot layer is poorly developed or lacking, and that pollen features do not support a separation of the Erdtmanithecales seeds and pollen organs.     

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.     

Pollen wall development in Cryptomeria japonica (Taxodiaceae)

Pollen wall development in Cryptomeria japonica was observed by scanning and transmission electron microscopy. The pollen of C. japonica is characterized by a non-saccate, projecting papilla. The exine of C. japonica consists of the outer granular ectexine and the inner lamellated endexine. At the tetrad stage, the initial granular layer of the pro-ectexine first forms on the microspore plasma membrane. The tripartite lamellae of the pro-endexine form under the pro-ectexine. The prosporopollenin material is deposited on the pro-ectexine and pro-endexine at the free spore stage. The ectexine granule increases its volume and the endexine lamellae thicken. The papilla protrudes during the tetrad stage. The tip of the papilla bends laterally where the exine is thinner. Exine construction in C. japonica is similar to that of Cunninghamia; however, the amount and size of the granular ectexine and lamellated endexine differ. The conspicuous papilla protrudes and bends during the tetrad period.     

POLLEN APERTURE EVOLUTION AMONG THE SUBFAMILIES PERSOONIOIDEAE,SPHALMIOIDEAE, AND CARNARVONIOIDEAE (PROTEACEAE)

Pollen apertures were analyzed among the subfamilies Persoonioideae (seven genera; ca. 95 spp.), Sphalmioideae (one genus; one spp.), and Camarvonioideae (one genus; two spp.). Pollen was examined by light microscopy, cryosection, and transmission electron microscopy. Completed studies of pollen apertures among Grevilleoideae (ca. 40 genera; ca. 800 spp.), one of two major subfamilies in Proteaceae, provide a basis for comparison and analysis of aperture evolution among these subfamilies. Aperture characters within Persoonioideae are unique among Proteaceae examined to date. Five distinct aperture types occur among the three subfamilies, three of which (Placospermum, Persoonia, Bellendena) are restricted to Persoonioideae. Sphalmioideae and Camarvonioideae each exhibit a unique aperture organization. The most primitive aperture organization, and one unique to Placospermum, exhibits three main features: 1) a thin, granular endexine continuous around the grain; 2) a heterogeneous foot layer throughout the grain with increased disruptions at the aperture; and 3) only slight differences in exine characters between apertural and nonapertural regions. The Persoonia aperture type represents the next stage of aperture evolution which involves loss of endexine, restriction of a heterogeneous foot layer to the aperture, and marked differences in exine characters between apertural and nonapertural regions. The uniformly homogeneous ektexine in both nonapertural and aperture regions in Bellendena has developed independently. Sphalmium exhibits a primitively thin granular endexine though the restriction of endexine to the aperture is a derived condition. Carnarvonia exhibits several pollen characters also found among Grevilleoideae including: 1) a homogeneous nonapertural ektexine; 2) a slightly heterogeneous apertural ektexine; 3) a lamellate/granulate endexine organized into irregularly shaped “clumps” clustered around the aperture; and 4) a clear demarcation between apertural and nonapertural exine. These characters support the hypothesis that Carnarvonia may have diverged early from the pre-Grevilleoids.     

Pollen wall development in Sciadopitys verticillata (Sciadopityaceae)

Pollen wall development of Sciadopitys verticillata was observed by transmission electron microscopy. The pollen of S. verticillata is non-saccate and spherical, and the exine consists of the outer thick, sculptured ectexine and the inner lamellated endexine. At the early tetrad stage, the initial ectexine and lamellae of the initial endexine begin to form on the microspore plasma membrane. The ectexine granules gradually swell. Deposition of sporopollenin materials on the ectexine granules then results it their becoming partially connected to each other. Identification of the original small ectexine granules then becomes difficult, and, finally, the ectexine appears as a homogeneous, partially discontinuous layer. The granules of the early ectexine cannot be identified. At maturity, there are four to five endexine lamellae. Recent molecular data have shown that Sciadopitys first branches off from the Cupressaceae plus Taxaceae clade, which is characterized by granular exine. Although the ectexine of Sciadopitys is similar to that of the Cupressaceae during initial development, the morphology of the ectexine is significantly different in the mature pollen. The initial stage of pollen development clearly shows the structural homology of the granular ectexine. Divergence of the exine structure occurs in the later stages.     

Pollen morphology in thePortulacaceae (Centrospermae)

Pollen of 110 species from 18 genera in thePortulacaceae has been examined by light and scanning electron microscopy, and a representative number by transmission electron microscopy. Three basic pollen types were found: 3-colpate with thick tectum and foot layer with prominent unbranched columellae and an extremely thin endexine; pantoporate with thick tectum and foot layer with branched columellae enclosing pores and an endexine that is one to two layers thick; pantocolpate with thin tectum and foot layer with broad, short unbranched columellae and an inconspicuous endexine. All pollen types, however, have a spinulose and tubuliferous/punctate ektexine. Also, all the genera except three,Calandrinia H.B.K.,Montia L. andTalinum Adanson are stenopalynous. There is, however, no absolute correlation between pollen morphology and geographical distribution, although both the major centre of palynological diversity and the majority of all species with tricolpate grains occur in South America.     

A unique pollen wall mutation in the family Compositae: ultrastructure and genetics

During a routine screening of pollen fertility in the n = 2 chromosome race of Haplopappus gracilis, a spineless pollen wall mutation was discovered that renders the otherwise functional pollen grains completely unrecognizable as Compositae pollen. Normal Haplopappus pollen is characterized by an outer layer, the ektexine, consisting of large spines supported by a roof (tectum), which in turn is supported by collumellae that are joined basally. A large cavity (cavea) stretches from aperture to aperture and separates columellae bases from the final ektexine unit, the foot layer. The spines, tectum, columellae, and columellae bases are filled with perforations (internal foramina), while the foot layer is without them. Immediately underlying the foot layer is a thickened, lamellate, disrupted, internal foramina-free second exine layer, the endexine. In contrast, the mutant pollen ektexine is a jumble of components with randomly dispersed spines as the only clearly definable unit. The endexine layer is similar to the endexine in normal pollen. The mutation apparently disrupts only the organization of ektexine units, and mutant pollen appears to be without the caveae and foot layer characteristic of normal pollen. In genetic tests, the mutant allele is recessive. There is a simple Mendelian pattern of inheritance of the mutant gene, and its phenotype is under sporophytic control.     

Some characteristics of pollen wall cytochemistry and ultrastructure in Japanese larch (Larix leptolepis Gord.)

Summary The mature pollen of Larix leptolepis Gord. (Conifer) contains five different cell types, and the plasma membrane of the vegetative cell is continuous and organized. The pollen wall is composed of two morphologically and cytochemically distinct domains: the exine and the intine. In the multilayered exine, the ektexine appears granular and the endexine, lamellar. The intine is thick and bilayered with a microfibrillar structure occupying its inner portion. Cytochemical reactions of the exine and the intine are similar to those found in angiosperms. Pollen wall involvement in the male female recognition system is discussed with respecl to the angiosperms.     

POLLEN MORPHOLOGY AND DETAILED STRUCTURE OF FAMILY COMPOSITAE,TRIBE CICHORIEAE. II. SUBTRIBE MICROSERIDINAE

A survey of pollen morphology of 40 species representing eight genera of the primarily North American subtribe Microseridinae reveals seven of the eight genera to have caveate, echinolophate, tricolporate grains, Picrosia being the only taxon with echinate pollen. Sectioned grains reveal the exine to consist of an ektexine and endexine. The ektexine, composed of spines, columellae, and foot layer appears to be of two basic types, one with six or seven levels of horizontally anastomosing columellae which are reduced to a single columellar layer under the paraporal lacunae and the second, a bistratified ektexine not reduced to a single layer below the paraporal lacunae. Sectioned exines of Pyrrhopappus are unusual, having very large columellae fused to the foot layer below ridges and highly reduced columellae under lacunae. Endexine organization is similar in most of the genera. Exceptions to this are Pyrrhopappus and some species of Agoseris, which have an “endexine 2” layer. Subtribe Microseridinae is essentially stenopalynous. The pollen data support most of the relationships suggested by Stebbins in his classification. The genera Agoseris, Microseris, Nothocalais, and Phalacroseris seem to form a natural group while Krigia and Pyrrhopappus form another cohesive series. The position of Picrosia, as an advanced offshoot of Pyrrhopappus, is not supported by the pollen data.     

Pollen wall ultrastructure and ontogeny in Heliotropium europaeum L. (Boraginaceae)

The pollen grains of Heliotropium europaeum are heterocolpate, with alternation of 3 colpori and 3 pseudocolpi. The exine is characterized by a scabrate and thick tectum, massive columellae with a granular appearance and a thick nexine. The thickening of the intine at the apertural level makes the interpretation of this zone difficult. The ontogenetic study helped to understand the ultrastructure of the exine and the apertures. The different steps are as follows. The primexine matrix is formed during the beginning of the tetrad stage; it consists of an outer thick and electron dense zone and an inner one, less dense to electrons. The tectum and the infratectum begin to form in the outer zone of the matrix, towards the middle of the tetrad stage. The infratectum consists of a network of columellae variable in thickness and oriented in different directions. The foot layer is lacking. The endexine is formed on a lamella system during the callose loss and microspore separation. The endexine becomes compact very early on its inner part. The apertures are initiated during the tetrad stage; a granulo-fibrillar oncus develops. At the free microspore stage, the oncus gets fibrillar and is bordered by endexine lamellae on its outer side and by endexine granulations on its inner one and laterally. The intine is set at the end of this stage. At the vacuolated microspore stage, the intine shows three layers: two thin, clear and homogeneous layers, one outside and the other inside, and a thick middle layer that forms the zwischenkörper, crossed by trabecula, in the apertural areas.     

Development of the pollen wall in Tsuga canadensis (Pinaceae)

In discussions of exine structural types, Tsuga is often mentioned as an exception, since no infratectal layer is present in the ektexine. The present investigation documents the formation of this pollen wall type at the ultrastructural level in T. canadensis . All layers of the exine are formed during the tetrad period, when the microspores are surrounded by a callose wall. The outer layer (ektexine) is elaborated on a fibrillar microspore surface coat, while the inner layer (endexine) is elaborated on lamellated structures. The deposition of the pretectum is followed by the appearance of endexine lamellae. In the initial stages, the two layers—pretectum and endexine—appear to be separated from each other only by a dense microspore surface coat. As additional wall materials are deposited, the tectal elements become convoluted and come to rest, in places, on the now recognizable footlayer. Upon release from the tetrad, intine formation begins and continuous accumulation of sporopollenin leads to an increase in ektexine thickness. The mature pollen wall of Tsuga canadensis , with a convoluted tectum resting directly on the footlayer, is characteristic of the genus.     

Pollen Organs and Seeds with Decussosporites Brenner from Lower Cretaceous Potomac Group Sediments of Eastern USA

Microsporangiate structures, Brenneria potomacensis gen. et sp. nov., containing pollen grains similar to dispersed Decussosporites are described from the Lower Cretaceous (Barremian or Early Aptian?) Potomac Group localities at Drewry's Bluff and Dutch Gap on the James River southeast of Richmond, Virginia. These fossils provide the first megafossil evidence of plants producing Decussosporites-type pollen and contribute important new information on the structure and possible systematic affinities of this unique Mesozoic gymnosperm. The microsporangiate structure is composed of an axis with helically arranged synangiate microsporangiate units, each unit consisting of two laterally fused sporangia borne on a short stalk. The pollen grains are very small, bisaccate, distinctly striate (taeniate) and TEM shows that they have partly infilled sacci (quasisaccate). These grains represent the youngest occurrence of saccate, striate pollen, which has not been recorded previously from sediments younger than the earliest Jurassic. Fossil seeds (Brennerispermum potomacensis gen. et sp. nov.) from the same localities as Brenneria contain Decussosporites pollen in the micropyle, and are believed to have been produced by the same plant species. The seeds are small and unitegmic with a distinct megaspore membrane. The occurrence of seeds adhering together in groups indicates that they were borne in aggregations. The microsporangiate structures of Brenneria show some similarity to those of the ginkgophytes (Ginkgoales and Czekanowskiales), but there are substantial differences in the structure of seeds and pollen. The Decussosporites pollen grains together with morphology of the reproductive organs support a closer relationship of the Brenneria-plant to previously described “Mesozoic pteridosperms”.     

POLLEN ULTRASTRUCTURE OF THE TRIBE INGEAE (MIMOSOIDEAE: LEGUMINOSAE)

All genera within the Ingeae, excluding Wallaceodendron, were examined with the transmission electron microscope. Thin sections reveal two pollen types (Types I and II) distinguished primarily by differences in polyad cohesion and ektexine organization. Type I polyads (only eight-grained species of Calliandra) are calymmate and the ektexine of individual cells is continuous around the grain, organized into a thin, foraminate tectum, irregularly shaped, often basally flared, foraminate columellae and thin, discontinuous foot layer. Type II polyads (16-grained species of Calliandra and remaining Ingeae) are predominantly acalymmate with individual grains typically free from one another or rarely, partially calymmate, i.e., individual grains show limited forms of attachment through small endexinous bridges (Pithecellobium latifolium [Zygia], Lysiloma) or localized appression of adjacent endexines (Pithecellobium daulense [Cathormion]). The adhesion of individual grains through localized fusion of lateral-distal and proximal ektexine in Enterolobium is unique among the partially calymmate Type II polyads. Ektexine in Type II polyads, largely restricted to the distal face, is composed of a thick, channeled tectum, granular interstitium and when present, thin discontinuous foot layer. Lateral-distal and proximal areas exhibit only endexine and, occasionally, a foot layer. The occurrence of nondistal ektexine is restricted to Enterolobium. The pollen data suggest that the acalymmate Ingeae polyads composed of grains with porate apertures, thick, highly channeled tectum, granular interstitium and lack of, or greatly reduced foot layer, are clearly derived within the Mimosoideae. Type I calymmate polyads appear to be independently derived. Ultrastructural data suggest that the Ingeae, excluding the eight-grained Calliandra species, represent a natural grouping with a close affinity to the Acacieae.     

Pollen morphology and pollen-wall proteins (localization and enzymatic activity) inSesamothamnus lugardii (Pedaliaceae)

The pollen grains ofSesamothamnus lugardii Stapf (Pedaliaceae of subdesert regions of SE tropical Africa) are associated in acalymmate tetrads (cross wall cohesion), with a tectate and perforate exine and 8–12 colpi. The pollen wall consists of an ectexine with a complete, perforate and ample tectum, columellated infratectum and clearly interrupted and fragmented foot layer. The endexine is built of scanty lamellae and granules. The intine is bistratificate, with a homogeneous, fibrillate layer (endintine or intine-2) and a heterogeneous, more lax and channeled layer (exintine or intine-1). Test for glycoprotein is particularly positive in the homogeneous internal intine and channels of external intine. On the other hand acid phosphatase has been localized in the exine and channeled external intine layers. These observations confirm the general interpretation of the distribution of wall compounds.     

Pollen wall development in Hypecoum imberbe Sm. (Fumariaceae)

We have studied the ontogeny of the pollen wall of Hypecoum imberbe. Our initial observations with conventional transmission electron microscopy (TEM) were inconclusive due to the similarities found in the electrodensity of the foot layer and the endexine, and between this latter layer and the intine. Thus we applied the PTA acetone histochemical test in order to differentiate between the cell wall components. This method proved to be efficient in resolving the differences between the layers and even allowed us to distinguish two strata within the narrow intine layer. A thin foot layer can be distinguished only by the temporary presence of a single white line separating it from the initial deposition of the endexine. The aperture consists of two colpi with no special differentiation. The tapetum is a typical secretory type giving rise to elaioplasts and tapetosomes during development, which persist as individual organelles upon the degradation of the tapetum. As the ultrastructural organisation of the sporoderm seems to offer little protection to the gametophyte, we finally discuss how the structure of the pollen sporoderm might be related to the special morphological characteristics of a flower, its habitat, and the biology of the plant as a whole.     

Conventional and novel modes of exine patterning in members of the Araceae – the consequence of ecological paradigm shifts?

Summary. In the family Araceae, the members of all subfamilies except Aroideae follow the conventional mode of exine formation pattern, which conforms with the textbook view of sporoderm stratification and chemistry (sporopollenin ektexine formed before the endexine). Only members of the subfamily Aroideae show a quite uncommon mode of exine formation pattern, with an endexine formed prior to the nonsporopollenin, polysaccharidic outer exine layer. The intine is formed simultaneously with this non-sporopollenin layer. From the differing timetable and especially from the different origin it is concluded that this outer exine layer is not homologous to the angiosperm ektexine. The fundamental question, why members of the Aroideae lack an elaborated sporopollenin ektexine, is discussed in terms of functionality of the nonsporopollenin outer exine layer. It seems that a major change in aroid evolution took place at the point when the family phylogenetically and ecologically shifted from bisexual (most subfamilies) to unisexual flowers (Aroideae only). The hypothesis is that ephemeral spathes and the absence of sporopollenin are the consequence of an adaptive syndrome for a short pollination time window in many members of the Aroideae, with short-lived pollen, an energetically not costly pollen wall, rapid germination of pollen tube, and brief receptivity of stigma. Correspondence and reprints: Institute of Botany, University of Vienna, Rennweg 14, 1030 Vienna, Austria.     

Pollen morphology of the subtribe Cuspariinae (Rutaceae)

The neotropical subtribe Cuspariinae (Rutaceae) comprises as many as 26 genera and over 125 species. Pollen grains from 111 collections representing 71 species and 24 genera were examined by LM, SEM, and TEM. The pollen morphology of this subtribe is very diverse. Grains are mostly 3–6-aperturate and colporate, rarely porate (Spiranthera) or pantocolporate (Almeidea). Exine sculpturing is most commonly reticulate, sometimes perforate, foveolate-perforate, foveolate, foveolate-reticulate, reticulate, striate-reticulate, echinate, clavate, or baculate. The exine structure is columellate and tectate-perforate, columellate and semitectate, or intectate and is stratified into ektexine and endexine. The exine ofLeptothyrsa is distinctive in that the ektexine of the mesocolpium is longitudinally deeply ridged. The pollen ofHortia, characterized by a psilate exine with rare perforations, a very thick foot-layer, and reduced columellae, is unlike that of any member of the Cuspariinae and offers no support for the transfer of this genus from the Toddalioideae. The pollen data correlate with macromorphological characters and are taxonomically useful.     

Pollen morphology in Campanulaceae IV

The exine structure has been studied in Campanulaceae s. lat. The results are combined with those in previous studies of shape, sculpturing and aperture conditions. Fifteen further species have been studied by SEM. Two main groups of pollen are found: (1) porate pollen with spinules and ridges/protrusions or a low relief reticulum, combined with an ektexine varying from simple to complex and a lamellated endexine; (2) 3–colpate/colporate pollen with a high relief reticulate/striate surface sculpturing, in general a homogeneous ektexine and an endexine lacking lamellae. The first group corresponds to Campanulaceae s. str., the second to Lobeliaceae s. str. Some genera like Cyananthus, Codonopsis and Parishella have unique characters which make them difficult to place in any of the two main groups.     

Pollen morphology and relationships of the Misodendraceae (Santalales)

The stem–parasitic family Misodendraceae is composed of a single genus, Misoden–drum , of 12 species endemic to the subantarctic Nothofagus forests of Chile and Argentina. Pollen of nine species was examined in the light microscope and scanning and transmission electron microscopes. Pollen is spheroidal (P/E 1 :1), sparsely echi–nate and polyporate. Aperture number is variable within and among species ranging from (3–)4–19 pores scattered randomly over the surface. Ultrastructurally, the pollen wall is composed primarily of endexine with the ektexine represented only by spines and an occasional thin granular layer between these elements. Pollen data indicate ties with the recently resurrected santalalean family Eremolepidaceae including Lepidoceras.     

EARLY CRETACEOUS TETRADS,ZONASULCULATE POLLEN,AND WINTERACEAE. I. TAXONOMY,MORPHOLOGY, AND ULTRASTRUCTURE

Ulcerate pollen tetrads from the late Barremian-early Aptian of Gabon, named Walkeripollis gabonensis gen. et sp. nov., resemble pollen of extant Winteraceae but have finer sculpture and a weakly calymmate tectum, like tetrads reported from the late Aptian-Albian of Israel. Scanning and transmission electron microscopy reveal additional winteraceous features (tall muri, short columellae, ring of endexine around the ulcus), plus segmented muri recalling the reticulate, zonasulculate to inaperturate genus Afropollis, which is abundant in the Aptian-Albian of Northern Gondwana. Afropollis also resembles Winteraceae in having tall muri and short columellae, but it has a thicker endexine. The new zonasulculate genus Schrankipollis, including S. mawhoubensis (Schrank) comb. nov. from the Aptian of Egypt and S. microreticulatus (Brenner) comb. nov. from the Potomac Group of Maryland, resembles Afropollis in structure of its muri but differs in its elliptical shape, finer reticulum, and restricted endexine.