Maria von Balthazar

Monetianthus mirus gen. et sp. nov., a Nymphaealean Flower from the Early Cretaceous of Portugal

Monetianthus mirus gen. et sp. nov. is described based on a single coalified flower from the Early Cretaceous (Late Aptian‐Early Albian) Vale de Agua locality, western Portugal. The flower is actinomorphic and probably bisexual, with a perianth of nine or 10 tepals, an androecium of 20 stamens, and a syncarpous gynoecium with a partly inferior ovary of 12 carpels arranged radially around a central column. Phyllotaxis of tepals and stamens is uncertain. Nondestructive synchrotron radiation x‐ray tomographic microscopy of internal structures documents laminar placentation with around six anatropous and ascending ovules in each locule. Comparison of Monetianthus with living plants indicates a clear relationship to extant Nymphaeales in particular with the Barclaya and Nymphaeoideae clade. Monetianthus thus provides evidence of crown group Nymphaeales, and probably crown group Nymphaeaceae, at a very early stage in the initial diversification of flowering plants.

Development of inflorescences and flowers in buxaceae and the problem of perianth interpretation

Recent phylogenetic analyses of angiosperms based on molecular and combined molecular and morphological data recognize a grade of basal eudicots situated between the ranunculids and the core eudicots. Buxaceae together with Didymelaceae form a well‐supported clade within this grade. Flowers of representatives of this grade are characterized by a considerable variability in organ number and organ differentiation. In particular, perianth evolution of basal eudicots has been difficult to interpret because of a high diversity in number and form of perianth organs. In this investigation, development and structure of inflorescences and flowers of representatives of all buxaceous genera were studied comparatively to gain a better understanding of flower structure in Buxaceae and their relationships to basal eudicots. Inflorescences of Buxus, Notobuxus, and Styloceras kunthianum are most often botryoids with several lateral male flowers and a terminal female flower. Inflorescences of Pachysandra and sometimes Sarcococca are open spikes with lateral male flowers in the upper part of the inflorescence and female flowers below them. In dioecious species of Styloceras, male flowers form long spikes that may be terminated by a peloric flower; female flowers occur singly or in thyrses. In Buxaceae, all phyllomes preceding the reproductive organs on an inflorescence axis or floral axis look superficially similar. They are bractlike, and no obvious differentiation between bracts and tepals can be observed. However, detailed comparative studies of plastochrons, phyllotaxis, size, and shape of organs on the whole reproductive shoot show slight differences between organs. Bractlike phyllomes, if present, preceding the reproductive structures of male flowers of all genera are arranged in a decussate pattern. They are initiated with short plastochrons within each pair, whereas the plastochrons between pairs are longer. The uppermost mainly four bractlike phyllomes show modifications in the direction of tepals. The two pairs of stamens in Buxus are initiated in the same pattern as the bractlike phyllomes, whereas in Sarcococca and Pachysandra the plastochron within each stamen pair is almost zero. In contrast, Notobuxus has six or eight and Styloceras has up to 45 stamens in a more complex arrangement. The remaining floral apex forms a more or less developed pistillode in Sarcococca, Pachysandra, and most Buxus species. The floral center of Notobuxus is less differentiated than in the other genera, whereas a pistillode is even lacking in a few Buxus species and in Styloceras. Carpels of Styloceras, Sarcococca, Pachysandra, Notobuxus, and often Buxus are preceded by an initial pair of transverse phyllomes (prophylls) and several spirally arranged bractlike phyllomes that are only weakly differentiated in the direction of tepals. The nature of these organs is discussed in a broader systematic context.

Phylogenetic relationships in Buxaceae based on nuclear internal transcribed spacers and plastid ndhF sequences

Sequences of nuclear internal transcribed spacers (ITS) and plastid ndhF from 25 representatives of Buxaceae were analyzed separately and in combination to resolve phylogenetic relationships among and within genera; parsimony and maximum likelihood methods were used. The results of the two single‐gene analyses were generally congruent, and the trees from the combined analysis were better supported. Two major clades were identified within the Buxaceae family: the clade of Pachysandra, Sarcococca, and Styloceras and the clade of Buxus and Notobuxus. Pachysandra and Sarcococca were two strongly supported monophyletic groups. The sister relationship between Sarcococca and the clade of Pachysandra and Styloceras was also strongly supported. American and Eurasian Buxus each formed a strongly supported clade. The controversial genus Notobuxus was embedded among African members of Buxus; B. hildebrandtii was sister to Notobuxus, with strong support. Relationships within Buxus and Sarcococca were only partially resolved.

Potomacanthus lobatus gen. et sp. nov., a new flower of probable Lauraceae from the Early Cretaceous (Early to Middle Albian) of eastern North America

A charcoalified fossil flower, Potomacanthus lobatus gen. et sp. nov., is described from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, USA. Internal floral structure was studied using nondestructive synchrotron-radiation x-ray tomographic microscopy (SRXTM). The flower is bisexual and trimerous. The perianth consists of two whorls of tepals. The androecium has two whorls of fertile stamens. Anthers open by two distally hinged valves. The gynoecium consists of a single carpel that is plicate in the style and ascidiate in the ovary and contains a single pendant ovule. The fossil flower shares many similarities with flowers of extant Lauraceae and is unlike flowers of other families of Laurales. However, the fossil flower also differs in detail from all extant or fossil Lauraceae, particularly in configuration of the androecium. The new taxon, together with previously described but more fragmentary material from the Puddledock locality, provides the earliest fossil record of plants more closely related to Lauraceae than to any other extant family. It reveals several derived morphological characters that are potential synapomorphies among extant representatives of the family Lauraceae and contributes to the growing evidence for an early diversification of Laurales before the end of the Early Cretaceous.

The ancestral flower of angiosperms and its early diversification

Recent advances in molecular phylogenetics and a series of important palaeobotanical discoveries have revolutionized our understanding of angiosperm diversification. Yet, the origin and early evolution of their most characteristic feature, the flower, remains poorly understood. In particular, the structure of the ancestral flower of all living angiosperms is still uncertain. Here we report model-based reconstructions for ancestral flowers at the deepest nodes in the phylogeny of angiosperms, using the largest data set of floral traits ever assembled. We reconstruct the ancestral angiosperm flower as bisexual and radially symmetric, with more than two whorls of three separate perianth organs each (undifferentiated tepals), more than two whorls of three separate stamens each, and more than five spirally arranged separate carpels. Although uncertainty remains for some of the characters, our reconstruction allows us to propose a new plausible scenario for the early diversification of flowers, leading to new testable hypotheses for future research on angiosperms.

Floral bract function, flowering process and breeding systems ofSarcandra andChloranthus (Chloranthaceae)

Structure and function of floral bracts, anthesis and breeding systems were investigated in greenhouse plants ofSarcandra chloranthoides, Sarcandra glabra, andChloranthus spicatus (Chloranthaceae). In early developmental stages the floral bract replaces the lacking perianth as a protective structure by enclosing the floral organs completely in a pocket-like structure, which is formed by the u-shaped attachment zone of the floral bract to the spike axis. The floral bract has a tip with an epithem tissue, from which traces of secretion seem to be released by the stomata. All species investigated have protogynous and longlasting flowers. The female phase begins five to seven days earlier than the male phase. It continues during the male phase and for some time thereafter. The male phase lasts between one day (Chloranthus spicatus) and seven days (Sarcandra chloranthoides). This is the first study on breeding systems of Chloranthaceae. They are of special interest in such a basal family of the angiosperms. Although the investigatedSarcandra andChloranthus species have similar flowers with entomophilous features, surprisingly their breeding systems are diverse:Sarcandra glabra is self-compatible,S. chloranthoides is agamospermous andChloranthus spicatus is self-incompatible.

Glandulocalyx upatoiensis, a fossil flower of Ericales (Actinidiaceae/Clethraceae) from the Late Cretaceous (Santonian) of Georgia, USA.

BACKGROUND AND AIMS Ericales are a major group of extant asterid angiosperms that are well represented in the Late Cretaceous fossil record, mainly by flowers, fruits and seeds. Exceptionally well preserved fossil flowers, here described as Glandulocalyx upatoiensis gen. & sp. nov., from the Santonian of Georgia, USA, yield new detailed evidence of floral structure in one of these early members of Ericales and provide a secure basis for comparison with extant taxa. METHODS The floral structure of several fossil specimens was studied by scanning electron microscopy (SEM), light microscopy of microtome thin sections and synchrotron-radiation X-ray tomographic microscopy (SRXTM). For direct comparisons with flowers of extant Ericales, selected floral features of Actinidiaceae and Clethraceae were studied with SEM. KEY RESULTS Flowers of G. upatoiensis have five sepals with quincuncial aestivation, five free petals with quincuncial aestivation, 20-28 stamens arranged in a single series, extrorse anther orientation in the bud, ventral anther attachment and a tricarpellate, syncarpous ovary with three free styles and numerous small ovules on axile, protruding-diffuse and pendant placentae. The calyx is characterized by a conspicuous indumentum of large, densely arranged, multicellular and possibly glandular trichomes. CONCLUSIONS Comparison with extant taxa provides clear evidence for a relationship with core Ericales comprised of the extant families Actinidiaceae, Roridulaceae, Sarraceniaceae, Clethraceae, Cyrillaceae and Ericaceae. Within this group, the most marked similarities are with extant Actinidiaceae and, to a lesser degree, with Clethraceae. More detailed analyses of the relationships of Glandulocalyx and other Ericales from the Late Cretaceous will require an improved understanding of the morphological features that diagnose particular extant groups defined on the basis of molecular data.

Floral structure and organization in Platanaceae.

Developing and mature inflorescences and flowers of several representatives of Platanus were studied to clarify various aspects of floral structure and organization. Special attention was given to perianth differentiation. Extant Platanaceae are monoecious with unisexual flowers aggregated into compact, spherical inflorescence heads. Development of hairs in a basipetal direction subdivides the undifferentiated inflorescence surface into floral zones. Development of both male and female flowers of Platanus × hispanica begins with the initiation of a perianth whorl. Thereafter, the reproductive organs emerge on the floral apex: stamens in male flowers, staminodes and carpels in female flowers. The last organs to appear in both sexes are the small organs located between perianth and androecium. At anthesis, in both male and female flowers, organs of the first whorl are inconspicuous, scalelike, and only two to three cell layers thick. Alternating with these first thin organs is a whorl of short but fleshy organs. These second‐whorl organs are basally united with the stamens, forming a short androecial tube. They also show some structural similarities with stamens. These features support the hypothesis that the second‐whorl organs are of androecial (staminodial) origin. This hypothesis is further supported by the fossil record, where, in some taxa, second‐whorl organs are particularly similar to stamens, as well as by morphological comparisons with flowers of Proteaceae.

Early Cretaceous floral structures and in situ tricolpate‐striate pollen: New early eudicots from Portugal

Five new taxa with affinities to extant lineages that diverged at an early stage from the main line of eudicot evolution are established from the Early Cretaceous (late Aptian or early Albian) Vale de Agua locality, Portugal. Staminate flowers of Lusistemon striatus and pistillate flowers of Lusicarpus planatus are unisexual without rudiments of the opposite gender. They are linked by the association of an unusual pollen type found in situ in the stamens and adhering to the stigmatic surface. The staminate flower, Lusistemon striatus, is composed of six stamens subtended by small perianth parts. The arrangement of the stamens is difficult to ascertain, but their variable sizes suggests a spiral arrangement. Pollen found in situ is tricolpate and striate with densely‐spaced, sparsely diverging and anastomosing muri that are aligned more or less parallel to the polar axis. The muri have a conspicuous supratectal ornamentation of fine transverse ridges. The granular infratectal layer forms an indistinct internal reticulum. The foot layer is thin. Pollen is closely similar to dispersed grains from the Aptian of Egypt described as STRIOTRI‐SEGMUR. It also resembles pollen of the dispersed pollen genus Rutihesperipites, as well as some dispersed pollen assigned to Striatopollis. Pistillate flowers of Lusicarpus planatus consist of a bicarpellate, syncarpous gynoecium borne on a short stalk. The styles are bent outwards and expose the double‐crested stigmatic regions on their ventral sides. The only organ preserved besides the gynoecium is a lateral scale‐like organ at the base of the stalk. Pollen of the same type found in Lusistemon striatus occurs on the stigmatic surface of the carpels. Comparisons with extant taxa demonstrate that Lusistemon and Lusicarpus share many characters with early diverging groups of eudicots, in particular Buxaceae. In addition to the Lusistemon‐Lusicarpus flowers, the Vale de Agua samples also contain three other pistillate reproductive structures that may be related to early diverging lineages of eudicots. Silucarpus camptostylus has a bicarpellate and syncarpous gynoecium with two styles; Valecarpus petiolatus and Aguacarpus hirsutus have tricarpellate gynoecia that are distinguished from each other in the shape and extension of the stigma as well as other details.

Carpestella lacunata gen. et sp. nov., a New Basal Angiosperm Flower from the Early Cretaceous (Early to Middle Albian) of Eastern North America

The charcoalified fossil flower, Carpestella lacunata gen. et sp. nov., from the Early Cretaceous (Early to Middle Albian) Puddledock locality, Virginia, has affinities to early branching lineages of extant angiosperms. The flower is small and actinomorphic. It shows ∼15 large basal scars, interpreted as those of tepals, and ∼60 smaller, quadrangular, distal scars, interpreted as those of stamens or staminodes. Both sets of organs are spirally arranged. The gynoecium is at least partly inferior and plurilocular, with 13 carpels arranged radially around a central column to which they are fused. The gynoecium is syncarpous, but the carpel flanks are partially free, and septal slits are present. Comparisons with extant angiosperms demonstrate similarities with flowers of Nymphaeaceae (especially Nymphaea) and also Illiciaceae (Illicium). The characters of the fossil may indicate that it represents a separate, now extinct phylogenetic lineage among the earliest branching lineages of extant angiosperms. Alternatively, the presence of septal slits, which links the fossil to Nymphaeaceae, makes it possible that the fossil is an extinct taxon within this family but distinct from all extant genera.