Pollen Organs Research Articles

Permotheca with in situ pollen grains from the Lower Permian of the Urals

Sporangial heads of the pollen organ Permotheca from the Lower Permian or Tschekarda, the Urals, are described as semisynangiate, with sporangia proximally connate for about one-third to half their length. The sporangial walls are three-layered and vascularized. The pollen grains, studied with LM, SEM and TEM are transitional protomonosaccate-bilobed to protobisaccate, sulcate, with alveolar infrastructure, lamellate nexine, and a tryphine-like surface layer. Chitrid zoosporangia occur in the pollen grains. The similarity to Idanothekion in the sporangial and pollen morphology may indicate phylogenetic relationships.

GIgantonoclea: an enigmatic Permian plant from North China

Gigantonoclea is a distinctive and enigmatic plant from the Permian of North China proper, with an unusual frond architecture and a pollen organ and vascular structure which are unique; it demonstrates a sudden rise and a rapid extinction. This paper reviews previous work on Asian gigantopterids and describes new material from the Upper Permian of Shanxi Province, including a new type of pollen organ (Jiaochengia lagrelii) and two new species of frond (Gigantonoclea crenataG. pubescens). Jiaochengia shows opposite, dissected and rather modified microsporophylls, laxly aggregating into an independent organ, which is markedly different from ‘Gigantotheca’ from Fujian. This presents evidence of heterogeneity among Asian gigantopterids and partly supports a relationship with the Carboniferous Callistophytales. Jiaochengia sporangia have what may be the first record of a waxy covering on the outer surface of a fossil plant, which is interpreted to have functioned to repel water, to protect against fungal attack and to scatter light. According to Hickey's rule, the venation of true Gigantonoclea fronds consists of three orders of main veins (rachis, midvein and secondary veins) and two orders of anastomosing veins (tertiary veins and veinlets). Certain putative ‘Gigantonoclea’ species from South China and some peripheral areas of North China do not have this type of venation and are thus excluded from the genus. Frond dimorphism is common among gigantopterids in both North and South China and can be compared with the amphibious variation from submerged to emergent leaves in extant aquatic plants. G. pubescens has a thick, bi‐layered adaxial cuticle with an indumentum covering with dense papillae and trichomes bases, and deeply sunken, papillate stomata, suggesting that it favoured more arid conditions. An observed gradient from pubescent to glabrate or even glabrous gigantopterid cuticle structures between North and South China suggests a change from xeric, mesic to humid habitats.

Aspects of Permian palaeobotany and palynology. XV. On the oldest known peltasperms with radially symmetrical ovuliferous discs from the Kungurian (uppermost Lower Permian) of the Fore-Urals (Russia)

Peltaspermum retensorium (Zalessky) Naugolnykh et Kerp, comb. nov., a new representative of the Peltaspermales, is described from the Kungurian of the Fore-Urals. Peltaspermum retensorium has radially symmetrical ovuliferous discs. The pollen organs are similar to those of other peltasperms. With regard to the frond architecture and the cuticle, the foliage of this plant appears to be very similar to that of Autunia Krasser emend. Kerp, a genus of peltasperms with bilaterally symmetrical megasporophylls, known from the uppermost Carboniferous and Lower Permian. Peltaspermum retensorium is the oldest true peltasperm with radially symmetrical ovuliferous organs known from Angaraland.

Eucommiitheca hirsuta, a new pollen organ withEucommiiditespollen from the Early Cretaceous of Portugal

Abstract A new pollen organ, Eucommiitheca hirsuta, containing Eucommiidites pollen grains is described from the Early Cretaceous of Portugal. The material comprises dispersed microsporangiate units and fragments of axes bearing microsporangiate units in an opposite and decussate arrangement. Each microsporangiate unit consists of a slightly angular to rounded peltate scale attached centrally to a short stalk, and with whorls of sporangia around the distal part of the stalk. Sporangia are stalked and free, with longitudinal dehiscence, and contain pollen grains similar to the characteristic dispersed pollen genus Eucommiidites. Eucommiitheca is comparable to Erdtmanitheca, another Cretaceous pollen organ containing Eucommiidites pollen, in the peltate nature of the microsporangiate units, but microsporangiate units in Erdtmanitheca are arranged in dense heads and sporangia are elongate. The opposite and decussate arrangement of the microsporangiate units in Eucommiitheca is in accordance with the possible...

The corystosperm pollen organ Pteruchus from the Triassic of antarctica

The permineralized corystosperm pollen organ Pteruchus is described from the early Middle Triassic of Antarctica. Pteruchus fremouwensis consists of an axis bearing numerous, helically arranged microsporophylls, each of which terminates in a distal flattened head. The axis is 1–2 mm in diameter and eustelic. Spherical to elliptical secretory cavities are present in the ground tissue of the axis, microsporophyll, and pollen sac wall. The basal stalk of the microsporophyll is vascularized by a C‐shaped strand that gives rise to a midvein and numerous lateral veins in the distal head. At least 38 pollen sacs are borne on the abaxial surface of the microsporophyll head. These are arranged in pairs on either side of lateral veins. Each pollen sac is sessile, elongated, and uniloculate. The pollen sac wall is several cell layers thick early in ontogeny, but reduced to a single layer in thickness when mature. Dehiscence is longitudinal along the inner surface. Pollen is monosulcate and bisaccate, and of the Alisporites‐type. The Triassic specimens are the first structurally preserved pollen organs of the Pteruchus‐type and can be related to the associated corystosperm stem and leaf genera based on the presence of unique secretory cavities. The morphology of Pteruchus and the relationship of this pollen organ with other Mesozoic and Paleozoic pollen organs is discussed.

The Corystosperm Pollen Organ Pteruchus from the Triassic of Antarctica

The permineralized corystosperm pollen organ Pteruchus is described from the early Middle Triassic of Antarctica. Pteruchus fremouwensis consists of an axis bearing numerous, helically arranged microsporophylls, each of which terminates in a distal flattened head. The axis is 1–2 mm in diameter and eustelic. Spherical to elliptical secretory cavities are present in the ground tissue of the axis, microsporophyll, and pollen sac wall. The basal stalk of the microsporophyll is vascularized by a C-shaped strand that gives rise to a midvein and numerous lateral veins in the distal head. At least 38 pollen sacs are borne on the abaxial surface of the microsporophyll head. These are arranged in pairs on either side of lateral veins. Each pollen sac is sessile, elongated, and uniloculate. The pollen sac wall is several cell layers thick early in ontogeny, but reduced to a single layer in thickness when mature. Dehiscence is longitudinal along the inner surface. Pollen is monosulcate and bisaccate, and of the Alisporites-type. The Triassic specimens are the first structurally preserved pollen organs of the Pteruchus-type and can be related to the associated corystosperm stem and leaf genera based on the presence of unique secretory cavities. The morphology of Pteruchus and the relationship of this pollen organ with other Mesozoic and Paleozoic pollen organs is discussed.

The morphology and ultrastructure of Caytonanthus

The morphology and ultrastructure of Caytonanthus arberi pollen organs and pollen, collected from the Middle Jurassic, Cayton Bay locality of England, are described. Pollen organs consist of flattened rachises with suboppositely branched pinnae, which bear terminal synangia. The synangium is covered with a two-zoned (fibrillar and amorphous) cuticle. The locule of each pollen sac is lined with a lamellated tapetal membrane and contains numerous pollen grains and orbicules. Grains are small, monosulcate, and bisaccate. Exine ornamentation of the proximal wall is psilate, while distally the apertural membrane is scabrate. The exine is composed of a thick, lightly staining sexine and a thin, darkly staining nexine. The sexine is tectate-alveolate laterally, becoming nearly homogeneous medially. The infratectal alveolae are robust and are continuous with the endoreticular units of the sacci. Sacci are eusaccate, with endoreticulations attached only to the outer walls. Several immature grains have also been identified and indicate that the nexine is lamellate throughout and that infratectal alveolae and nexine lamellae are well developed prior to complete tectum synthesis. Saccus size and ultrastructure of Caytonanthus pollen are compared with those of other Late Paleozoic and Mesozoic seed ferns that produced saccate pollen (Callistophytales, Glossopteridales, Corystospermales) and found to be smaller and more extensively filled with thicker endoreticulations. Documentation of the eusaccate character state in Caytonanthus is also discussed regarding its phylogenetic implications. Key words: Caytonanthus, Caytoniales, Mesozoic, pollen, seed fern, ultrastructure.

A synopsis of medullosan pollen organs from the middle Pennsylvanian Mazon creek flora of northeastern Illinois, USA

Six kinds of medullosan pollen organs containing Monoletes-type pollen (prepollen) are described from the middle Pennsylvanian Mazon Creek flora of northeastern Illinois, USA. Codonotheca caduca Sellards and Schopfitheca boulayoides Delevoryas are redescribed and emended diagnoses and new reconstructions are provided. Three forms of Dolerotheca-type pollen organs are described for the first time, along with ultrastructural details of in situ pollen. A sixth kind of pollen organ, tentatively associated with the ovule Stephanospermum konopeonus (Langford) Drinnan, Schramke and Crane, is too poorly preserved for generic assignment but has pollen different from that of other Mazon Creek medullosan pollen organs. This new information on Mazon Creek plants provides important evidence on the diversity of medullosan “pteridosperms” in the flora. Characterization of in situ pollen provides a basis for continuing attempts to associate pollen organs with the variety of co-occuring dispersed ovules.

Pollen morphology and ultrastructure of the corystospermales: permineralized in situ grains from the triassic of Antarctica

Corystosperms, represented by Dicroidium leaves and Pteruchus-like pollen organs, are major components of the Early-Middle Triassic silicified flora from the Fremouw Formation of Antarctica. The micromorphology and ultrastructure of the in situ pollen contained within these organs are described. Pollen sacs of varying ontogenetic ages have been isolated. Mature grains are monosulcate and bisaccate, with large, crescent-shaped eusacci. The exine is relatively thick in the cappa region and thins toward the distal sulcus; surface ornamentation is psilate. In medial positions of the proximal wall, the exine is homogeneous but becomes tectate-alveolate in more lateral regions of the cappa. The alveolar units extend into the sacci forming an endoreticulum; however, the endoreticulations are discontinous and only attach to the outer walls of the sacci. A wedge-shaped unit, where the sacci attach to the corpus, characterizes both the proximal and distal poles. The sulcus is broad, extends the entire width of each grain, and is longitudinally flanked by elevated lips. The structural features of these grains are discussed with respect to other fossil and extant saccate pollen. The grains are systematically compared with those of other bisaccate pollen-producing plants with which the Corystospermales have been suggested to be closely related, including Glossopteridales, Caytoniales, and angiosperms (Lactoridaceae). The permineralized in situ grains are also compared with other compressed Pteruchus species known at the ultrastructural level and with morphologically similar dispersed palynomorphs known from Antarctic sediments.

Pollen Organs and Seeds withDecussosporitesBrenner from Lower Cretaceous Potomac Group Sediments of Eastern USA

Abstract 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 th...

Saharatheca lobata n. gen. and sp.: a new medullosan (seed fern) pollen organ from the Middle Pennsylvanian of Illinois

Several specimens of a pollen organ containing Monoletes pollen occur in a single coal ball collected from the Herrin No. 6 Coal at the Sahara Coal Company Mine in southern Illinois. Specimens are 3–4 cm long, up to 1 cm wide, and are either bilobed or trilobed; 5–7 pollen sacs are arranged along each side of a discontinuously sclerified ground tissue plate extending into each lobe. The vascular supply from the peduncle breaks up by repeated dichotomies and one bundle descends along the outer side of each pollen sac. The mode of dehiscence and the structure of the tip of the organ remain unknown. Each lobe (and contained sporangia) is hypothesized to be derived from an ancestral fertile frond segment bearing pendulous sporangia.

Pollen Organs and Seeds withEucommiiditesPollen

Abstract The characteristic Mesozoic pollen genus Eucommiidites is described from pollen organs and seeds recovered in Cretaceous strata of North America and Europe. The pollen organs are from the lowermost Upper Cretaceous (Cenomanian) of Texas and are referred to Erdtmanitheca texensis gen. et sp. nov. They are spherical heads, composed of numerous, densely crowded, radiating pollen sacs that contain abundant well-preserved pollen. Combined LM, SEM and TEM investigations show that the pollen grains each have a distinct distal colpus flanked by two lateral colpi in an equatorial position. Pollen wall ultrastructure is gymnospermous with a thick lamellate inner layer (endexine) and an outer layer (ektexine) composed of a granular inner part and a homogeneous outer part. The endexine is thickened in the region of the colpi. Small seeds from the Lower Cretaceous (upper Berriasian to Valanginian) of Bornholm, Denmark contain abundant Eucommiidites pollen in their micropyles. The seeds are referred to Erdtman...

The morphology and phylogenetic significance of Vardekloeftia harris (Bennettitales)

The genus Vardekloeftia Harris, a bennettitalean reproductive structure from the Upper Triassic of East Greenland, is reinvestigated from the original material and from more recent collections. The two previously described species are combined as V. sulcata Harris and new generic and specific diagnoses, as well as more detailed descriptions, are provided. In the ovule of Vardekloeftia the nucellus is surrounded by two distinct layers (integument and cupule). Comparisons indicate that this kind of ovule structure also occurs in other Bennettitales and may be general within the group. The probable leaves of the Vardekloeftia plant are Pterophyllum kochii Harris. The pollen organs are unknown, but Bennettistemon amblum Harris and Bennettistemon ovatum Harris are associated with Vardekloeftia and clumps of pollen very similar to that of these species occur in the micropyles of Vardekloeftia seeds. Comparison of Vardekloeftia with other Bennettitales suggests that pollination and dispersal may have been relatively unspecialized in this early member of the group.

Meeusella and the origin of stamens

Meeusella gen. nov. is a strobilate pollen organ from the Lower Cretaceous of Transbaikalie (east of the Lake Baikal); the branched lateral branches (paracladia), if fully developed, bear a subterminal pair of stalked synangial heads. In some cases the latter are reduced to a pair of sessile heads or the paracladia are sterile. It is suggested that the synangial heads might be further reduced to a pair of bisporangiate thecae, while the paracladium apex between them might form a prominent connective of a typical stamen. ▭Androecium, androclade, angiosperms, proangiesperms, stamen, evolutionary morphology.

Gnetalean plants from the jurassic of Ust-Balej, East Siberia

The gnetalean affinity of the samaras described by Heer (1876) as Ephedrites antiquus is supported and a new generic name Heerala is proposed for them. They are conceived as borne axillary to the bracts of a new bract genus Angarolepis. The Ephedra-like leaves from the same locality, assigned to a new leaf genus Cadmisega, might belong to the same plant. Its supposed pollen organs have previously been described as Kaidacarpum, a monocot fruit, and Equisetostachys, a spore cone.

Melissiotheca: a new pteridosperm pollen organ from the Lower Carboniferous of Scotland

Melissiotheca is based on fusainized pollen organs of pteridospermous affinities which occur abundantly in an Upper Visean limestone at Kingswood, near Pettycur (Scotland). The new species is a pedicellate synangium composed of 50–150 sporangia each of which is embedded at its base in a parenchymatous cushion divided into lobes. The sporangia are fused along their proximal half but are free distally. Dehiscence is longitudinal. Each sporangium is supplied at its base by a single vascular strand. Prepollen is small, spherical and trilete with a rugulate exine. In ultrastructure, the nexine appears homogeneous; the sexine shows internal sculpture of granae and rod elements. Melissiotheca has not been assigned to any family, but it shows many affinities with pollen organs attributed to the Lyginopteridaceae.

Studies on a new lower carboniferous flora from kingswood near pettycur, Scotland. I. Preliminary report

A new Asbian flora preserved as calcareous permineralizations and as fusian has been discovered closely associated with the famous Pettycur flora in Fife, Scotland. This new flora occurs in limestones within a volcanogenic sequence at Kingswood, near Pettycur. The limestones are tentatively interpreted as having been deposited in a lake possibly within a crater. The plant fossil assemblage is dominated by fusainized pteridospermous remains which include stems, rachides, distal parts of fronds and pollen organs. Associated with these are numerous fragments of gymnospermous wood. Permineralized axes of the lycopod Oxroadia are also abundant and occur with megasporophylls of Achlamydocarpon-type. Sphenopsids and ferns are rare and always fusainized. The assemblage contains new taxa still to be named, such as two pollen organs showing intermediate features between Lyginopteridaceae and Medullosaceae and at least two species of Lyginorachis. Some gymnospermous stems with pycnoxylic wood and triangular pith also represent new taxa of unknown affinities. The occurrence of growth rings in some woody specimens is noted. Whilst this flora is of the same age as the Pettycur assemblage, the most significantly striking feature is that there is only one genus, Archaeocalamites, in common. This almost certainly must reflect an ecological control within the volcanic terrain.

Studies on a lower carboniferous flora from kingswood near Pettycur, Scotland. II. Phacelotheca, a new synangiate fructification of pteridospermous affinities

Phacelotheca pilosa gen. et sp. nov. is described from Kingswood, a locality of Upper Visean age near Pettycur. The fructification was borne laterally on a stalk and dichotomizes several times in a cruciate arrangement. Presumed reduction and overtopping has resulted in aggregation of the synangia which are arranged in tiers at the extremity of foreshortened branch axes. Each synangium is composed of two to four elongate sporangia with longitudinal and ventral dehiscence. Each sporangium is supplied at its base by a single vascular strand. The spores are small, spherical and trilete with a wall differentiated into a nexine and sexine; the sexine is granular to granular-alveolar. In many features, Phacelotheca pilosa resembles pollen organs attributed to Lyginopteridaceae. The current status of the genus Telangium is discussed.

A monograph of Dolerotheca Halle, and related complex permineralised medullosan pollen organs

ABSTRACTNumerous permineralised, complex medullosan pollen organs are described from Middle and Upper Pennsylvanian sediments of North America. Together with a reinvestigation of type specimens for the previously described species, these provide the basis for fully characterising internal structure and external morphology, and for recognising structural homologies among all medullosan synangia. All medullosan pollen organs, simple and complex, can be interpreted as consisting of sporangial tubes that are embedded in parenchymatous and sclerenchymatous ground tissue, and that have vascular bundles within the parenchymatous tissue. The sporangial tubes are arranged in a single series, usually a ring, with parenchymatous ground tissues and vascular bundles to the outside of the ring and sclerenchymatous ground tissue to the inside of the ring. In the larger, complex forms the ring is plicately folded and there may be a centrally-placed hollow in the distal surface. Differences in morphology, in the folding pattern of the rings, in the structure (or absence) of a distal hollow, and in architecture of the major vascular system are employed to delimit genera. Size and shape of the organ, histological features, numbers of sporangia, and presence or absence of lacunae are used to delineate species. Currently recognised genera are Dolerotheca Halle, Sullitheca Stidd et al., Stewartiotheca Eggert and Rothwell, and Bernaultia gen. nov.

BOULAYATHECA, THE NEW NAME FOR THE SEED FERN POLLEN ORGAN BOULAYA CARPENTIER

In 1914 Carpentier described microsporangiate organs from the Houiller du Nord of France under the binomial Whittleseya (?) fertilis, a name which had earlier been used by Kidston (1914) for specimens collected from the Staffordshire Coal Fields near Dudley, England. Several years later (1925) Carpentier re-evaluated the specimens and assigned them to a new genus, Boulaya. However, it is not clear by his reference as to which specimens were transferred to Boulaya. In addition the generic name Boulaya was not used in combination with a specific epithet. In 1933, Halle attempted to rectify the problem and proposed that the specimens previously designated Whittleseya (?) fertilis Kidston be renamed Boulayafertilis. Since that time the generic name Boulaya has been used for simple pyriform pollen organs of Westphalian age measuring up to 1.7 cm and consisting of several, elongate sporangia arranged in a ring. Because of the nature of the preservation (impression-compression), and the absence of sufficient morphological characters with which to define the taxon, there has been some discussion as to whether Boulaya is different from other simple pteridosperm pollen organs (e.g., Millay and Taylor, 1979). However, in a recent contribution the ultrastructure of Monoletes pollen extracted from Boulaya fertilis was compared with grains from morphologically similar pollen organs (e.g., Aulacotheca, Halletheca, Schopfitheca). In this paper we provided additional evidence that the pollen organ Boulaya is a distinct taxon (Kurmann and Taylor, 1984). It has recently been brought to our attention that Boulaya Carpentier (1925) is a later homonym of Boulaya Cardot (1912), a generic name applied to a moss included in the Leskeaceae. According to Article 64.1 of the International Code of Botanical Nomenclature (1983) the generic name Boulaya Carpentier (1925) must be rejected as being illegitimate (Stafleu, 1983). We therefore propose that the name of the pteridosperm pollen organ be changed from Boulaya to Boulayatheca. The generic and specific diagnoses used by Halle (1933) remain the same.