Michael A. Millay

Paleozoic seed fern pollen organs

Paleozoic pollen organs exhibit numerous morphological forms that have been arranged in categories based on their probable organization. Progymnosperm ancestors are characterized by three dimensional branching systems bearing pairs of terminal sporangia. Early Mississippian examples of seed fern fertile branches appear little modified from the progymnosperms. These pteridosperm microsporangia are nonsynangiate and thin walled with longitudinal dehiscence. By Upper Mississippian time all forms show sporangial clustering into large or small groups, with several taxa exhibiting radially symmetrical synangia. In the Lower Pennsylvanian all pollen organs are synangiate and appear to consist of a uniseriate ring of sporangia that either surround a central hollow, or are bilaterally flattened. Sporangial dehiscence in all forms is longitudinal and toward the center of the synangium. In bilateral synangia with no central hollow, the sporangia either separate laterally or effective dehiscence areas are restricted to the free apical portions of the sporangia. Callistophytacean synangia resemble the lyginopterid type, but are abaxial on laminar foliage. This family is thought to have evolved from the lyginopterids during the Early Pennsylvanian. Middle Pennsylvanian medullosan pollen organs are all radial and may be solitary, aggregated into groups, or fused into a large compound synangium. Several pollen organ types are reinterpreted, and the possible evolutionary relationships among the various Paleozoic pollen organ forms are discussed based on synangial organization, patterns of frond branching, and pollen or prepollen morphology.RésuméLes organes à pollen de l’ère paléozoique manifestent nombreuses formes morphologiques qui permettent une catégorisation basée sur leur organisation probable. Les ascendants sont des progymnospermes et sont caractérisent par un système de branchement à trois dimensions qui se termine par des sporanges disposés en paires. Les microsporanges des ptéridospermes du début de la période Mississippienne révèlent peu de différence d’avec ceux des progymnospermes. Les microsporanges des ptéridospermes nonsynangiates (pas fusionnés) présentent des parois minces et une déhiscence longitudinale. A partir de la deuxième moitié de la période Mississippienne toutes les formes manifestent un regroupement de sporanges en larges ou petits groupes et plusieurs taxons manifestent des synanges a symétrie rayonnée. Dans la première période Pennsylvanienne, tous les organes à pollen sont du genre synange et semblent se composer d’un anneau unisériel de sporanges qui soit entoure un creux central, ou soit s’aplatit de façon bilatérale. La déhiscence sporangiale sous toutes ses formes est longitudinale et orientée vers le centre du synange. Parmi les synanges de type bilatéral, dépourvu de creux central, les sporanges soit se divisent bilatéralement ou manifestent des lieux de déhiscence qui sont limités à la partie apicale des sporanges. Les synanges de la famille Callistophytacéenne ressemblent au type lyginoptéride, mais sont abaxiaux sur feuillage laminaire. Cette famille est supposée avoir évoluée à partir des lyginoptérides au début de la période Pennsylvanienne. Vers le milieu de cette même période, les organes à pollen genreMedullosa sont tous radiaires et peuvent être solitaires, regroupés, ou fusionnés en un large synange composé. Plusieurs types d’organes à pollen sont réexamines, et les rapports évolutionnaires possibles parmi les formes d’organes à pollen de l’ère Paléozoique sont discutés, basés sur l’organisation du synange, sur le branchement des frondes, enfin sur la morphologie du pollen ou prépollen.ZusammenfassungPaleozäne Blütenstauborgane weisen zahlreiche morphologische Formen auf, die auf Grund ihrer wahrscheinlichen Organisation in Kategorien aufgeteilt worden sind. Die Urtypen heißen Progymnospermen und sind durch sich in drei Dimensionen abzweigende Systeme gekennzeichnet, die paarweise Endsporangien tragen. Bei Proben der Samenfarnpflanzen aus der frühen Mississippi-Zeitepoche scheinen fruchtbare Zweige von denen der Progymnospermen wenig abmodifiziert. Diese Mikrosporangien der Pteridospermen sind nichtsynangiatisch und haben dünne Wände mit Längsaufspringen. Bis zur Ober-Mississippi-Zeitepoche sammeln sich die Sporangien aller Formen in große oder kleine Gruppen; die Sporangien mehrerer Taxus weisen eine strahlenförmige Symétrie auf. In der Nieder-Pennsylvania-Zeitepoche sind alle Blütenstauborgane synagiatisch: sie bestehen anscheinend aus einem einreihigen Kreis von Sporangien, die entweder eine zentrale Höhle einkreisen oder sich beiderseitig abflachen. Das Aufspringen der Sporangien in allen Formen ereignet sich der Länge nach und auf die Mitte des Synangiums zu. Bei zweiseitigen Sporangien mit keiner Höhle lösen sich die Sporangien zur Seite, oder die wirkenden Gegenden des Aufspringens sind auf die freien an der Spitze befindlichen Teile der Sporangien beschränkt. Kallistophytozäne Synangien gleichen den lyginopteridischen Typen, sie sind aber nichtaxial und befinden sich auf blättrigem Laubwerk. Diese Familie, denkt man, habe sich aus den Lyginopteriden während der frühen Pennsylvania-Zeitepoche entwickelt. Markige Blütenstauborgane der Mittel-Pennsylvania-Zeitepoche sind alle strahlenförmig und dürfen einzeln, in Gruppen aggregiert, oder in einem großen zusammengesetzten Synangium zusammengeschmolzen sein. Mehrere Typen der Blütenstauborgane werden neuerklärt, und mögliche Evolutionsverhältnisse der verschiedenen Formen von paleozänen Blütenstauborganen werden auf Grund der Synangienorganisation, der Muster von Blätterabzweigung und der Blütenstauboder Vorblütenstaubmorphologie besprochen.ResumenLos órganos Paleozoicos portadores de polen, exhiben una variada morfología que ha sido ordenada en categorías, basándose en su probable organización. Los antecesores progimnospérmicos están caracterizados por sistemas ramificados tridimensionales que portan pares de esporangios terminales. Muestras del Mississippiano temprano de ramificaciones fértiles de helechos con semillas, parecen poco modificadas en relación con las Progimnospermas. Estos microsporangios pteridospérmicos son nosinangiados y con paredes delagadas con dehiscencia longitudinal. En el Mississippiano superior todas las formas muestran esporangios agrupados en grandes o pequenos grupos, con algunos taxa que exhiben sinangios con simetria radial. En el Pennsylvaniano temprano, todos los órganos portadores de polen son sinangiados y parecen consistir en un anillo uniseriado de esporangios que rodean un hueco central o se disponen en forma de anillo achatado. La dehiscencia de los esporangios en todas las formas es longitudinal y hacia el centro del sinangio. En los sinangios bilaterales sin hueco central, los esporangios se separan lateralmente o las áreas efectivas de dehiscencia están restringidas a las porciones apicales libres de los esporangios. Los sinangios de las Callistophytaceas parecen de tipo lyginopteroideo pero están en la parte abaxial de la lámina foliar. Se cree que esta familia ha evolucionado de las Lyginopteroideas durante el Pennsylvaniano temprano. Los órganos portadores de polen de las medullosas del Pennsylvaniano medio son todos radiales y pueden ser solitarios, agregados en grupos o fusionados en grandes sinangios compuestos. Basándose en la organizatión sinangial, los patrones de ramificación de las frondes y la morfología del polen o del prepolen, algunos tipos de organos portadores de polen son reinterpretados y se discute las posibles relaciones evolutivas entre las formas de órganos portadores de polen del paleozoico.АБСТРАКТПалеозойские пыльце вые органы представл ены многочисленными морфологическими фо рмами, которые могут б ыть распределены по категориям в завис имости от их предпола гаемого устройства. Происшед шие от прогимносперм ных характеризуются тремя типами систем в етвления, несущими па ры терминальных спорангий. Ранне-Мисс исипские образцы пло досеменных папоротниковых ветв ей мало чем отличаютс я от прогимноспермных. Да нные папоротникосем енные микроспорангии не синангируют и тонк о перегорожены продо льным растрескиванием. К на чалу Верхне-Миссисип ского периода все формы демонстрируют спорангиальные скоп ления в большие и малые группы с отдель ными построениями, представляющими радиально симметрич ные синангии. В Нижне-Пенсильвански й период все пыльцевые органы синангируютс я и представляются как содержащие однос ерийный круг споранг ий; они либо окружают центральную полость, либо дву сторонне спл ющены. Спорангиальное раст рескивание во всех фо рмах продольно и направлено к центру с инангии. В двусторонн е сплющенных синангиях без центра льной полости споран гии либо разделяются по бокам, либо эффекти вные районы растреск ивания ограничены свободны ми верхушечными порц иями спорангий. Каллистофитовые син ангии напоминают лигиноптеридный тип, однако направлен ы в сторону от оси на сл оистой листве. Предполагается, что э то семейство развило сь из лигиноптеридов во время Ранне-Пенсил ьванского периода. Средне-Пенсильванск ие сердцевинные пыльце вые органы могут быть лучеобразнорасходя щимися или же одиночными, соб ранными в группы, либо слиты в бо льшой сложный синанг ии. Отдельные типы пыльцевых орган ов рассмотрены занов о, возможные эволюционные отноше ния различных форм па леозойских пыльцевых органов обсуждены в з ависимости от синанг иального устройства, рисунков листов папоротника, а также пыльцевой и допыльцевой морфол огии.

Pollination biology and reproduction in early seed plants

Abstract The current level of understanding regarding the reproductive mechanisms operative in early seed plants is reviewed. Information is presented that details aspects of pollination biology including pollen morphology, pollen release, possible mechanisms of transfer, and the method of pollen capture. Speculation is offered regarding the importance of ovule position as related to potential insect pollination vectors in these early seed plants. Post-pollination events in Paleozoic seed plant reproduction including micro- and megagametophyte development, fertilization, and post fertilization stages are extrapolated from the fossil record.

Morphologic variability of Pennsylvanian lyginopterid seed ferns

Abstract The current level of understanding of the morphological variability of Pennsylvanian lyginopterid seed ferns is reviewed. This group of pteridosperms that ranges throughout the Carboniferous is represented by a heterogeneous assemblage of stems, leaves, ovules and pollen organs. Vegetative organs have been useful in tracing the origin of the eustele from a protostele, while the fern-like fronds appear to have had their origin from a non-planated branching system. The small radially symmetrical ovules, while exhibiting some diversity in the organization of integument, demonstrate little apparent alteration in pollen-receiving mechanisms and reproductive versatility. Lyginopterid pollen organs are synangiate and include both radial and bilateral forms. The stratigraphically earliest types are radial and borne upright on naked branches, while later forms are usually bilateral and typically associated with laminar foliage. Pollen is morphologically and structurally similar to the spores of many ferns, and probably germinated through the proximal suture. The apparent homogenous nature of lyginopterid seed ferns may indicate that relatively little evolution had taken place over a long geological time span. However, evidence from some compression floras suggests that far more diversity exists within the order in a non-swamp environment than had previously been thought. Current concepts about lyginopterid pteridosperms that have been developed from a small group of plants in a relatively homogeneous environment may need considerable revision as we learn more about the non-swamp inhabiting forms.

New fern stems from the Triassic of Antarctica

Five new genera of filicalean fern stems are described from Antarctic silicified permineralizations of early Middle Triassic age. Antarctipteris gen. n. stems are rhizomatous, 5–15 mm in diameter and possess an exarch protostele. Leaf traces are initially bar-shaped and become C- or V- shaped in the petiole. The stele and leaf traces are surrounded by cortical sclerenchyma strands. Fremouwa gen. n. is a creeping rhizome 1–4 mm in diameter which possesses an endarch, ectophloic siphonostele. C-shaped leaf traces are produced radially and migrate through the cortex obliquely. Schleporia gen. n. stems are 3–4 mm in diameter and possess a mesarch ectophloic siphonostele. Branching occurs by initiation of two C-shaped xylem strands that fuse adaxially and then abaxially to form a cylinder. Leaf traces are C-shaped and distantly spaced. Schopfiopteris gen. n. is a creeping rhizome 1.5–11 mm in diameter which possesses an endarch, ectophloic siphonostele. Stems produce C-shaped leaf traces on one side of the stele. Soloropteris gen. n. stems are cylindrical, 1–4 mm in diameter, and possess a mesarch amphiphloic siphonostele which produces C-shaped leaf traces. Lateral buds are axillary or adaxial to the widely spaced leaves. The stems are compared anatomically to Paleozoic filicalean ferns and an attempt is made to suggest relationships to extant families within the Filicales.

Evolutionary trends in fossil gymnosperm pollen

Abstract The evolution of cordaite, conifer, and cycadophyte pollen types are discussed relative to germination polarity, external ornamentation, suture organization, saccuscorpus development, and sporoderm ultrastructure. Information is presented in which the development of the microgametophyte is considered together with an analysis of the reproductive biology of several taxa.

Phi Thickenings in Fossil Seed Plants from Antarctica

Primary anatomy and secondary development is described for two root types from the Fremouw Peak locality (Transantarctic Mts, Antarctica) of early to middle Triassic age. Roots of Antarcticycas have a bilayered cortex with thick surface cuticle, diarch xylem, and a clearIy defined endodermis surrounded by a single cell layer possessing phi thickenings. Secondary development begins with phellern and phelloderm production from the out er primary phloem position, and is followed bya bifacial vascular cambium next to the primary xylem that pro duces sieve cells and ray parenchyma to the outside. Young roots of Antarcticoxylon are similar to those of Antarcticycas, but may possess 2-3 cell layers with phi thickenings. Secondary development from a bifacial vascular cambium produces alternating bands of sieve cells and phloem parenchyma cells in the secondary phloem and wood with uniseriate rays and scattered axial parenchyma. The presence of phi thickenings and an epidermal cutieie in both roots suggests environmental stress related to water regulation. The occurrence of phi thickenings in the roots of some conifers, angiosperms, a fossil cycad and a probable seed fern suggests this character is of ecological rather than phylogenetic significance.

Fertile and sterile frond segments of the lyginopterid seed fern Feraxotheca

Abstract Fertile and sterile frond segments of the lyginopterid seed fern Feraxotheca culcitaus are described. In both the fertile and sterile specimen three orders of frond axes are borne alternately and in the same plane. Antepenultimate and penultimate frond axes are characterized by a C-shaped vascular bundle and numerous canals containing a golden-colored material in the fossilized condition. Synangia with only four sporangia demonstrate radial symmetry; bilateral symmetry is present in larger synangia. Pinnules possess dichotomous venation, with a single vein entering each lobe of the deeply incised lamina. A single canal occurs below each vein, and vein ends have an amplified vascular bundle. Morphologically Feraxotheca compares most closely with the compression genus Crossotheca . The morphology of the vascular bundle in the largest pinna is similar to a Lower Carboniferous specimen of Rhodea .

The ultrastructure and reproductive significance of Lasiostrobus microspores

Abstract The normally inaperturate microspores of the Pennsylvanian cone Lasiostrobus are found to rarely possess trilete sutures, confirming the subequatorial position of the sacci. Sporoderm ultrastructure compares favourably with saccate pollen of some extant members of the Coniferales. The shedding of grains in the microspore stage suggests that microgametophyte evolution had passed the stage of prothallial cell production, and that Lasiostrobus is an advanced member of the Paleozoic gymnosperm complex.

Studies of Living and Fossil Saccate Pollen Grains

Pennsylvanian synangiate fructification Idanothekion glandulosum and five species of the extant genus Picea, morphological and microtopographical features, scanning electron microscope, Illinois