Mário Miguel Mendes

Acclimation of Myrtus communis to contrasting Mediterranean light environments - effects on structure and chemical composition of foliage and plant water relations.

Leaf anatomical and chemical characteristics, water relations and stomatal regulation were studied in the shrub Myrtus communis growing under two contrasting Mediterranean light environments (full light versus 30% of full light) during the spring-summer period. These studies aimed to assess plant response to the combined effects of light and water availability. Foliar morphology, anatomy and chemistry composition acclimated positively to light conditions. Leaves of sun-exposed plants were thicker (38.7%) than those of shaded plants, mainly due to increased palisade parenchyma thickness, had a higher nitrogen concentration and stomatal density than the shade ones, which maximized foliar area (>SLA) and Chl/N molar ratio to improve light interception. Chlorophyll concentration per leaf area (Chl(a)) was always higher in sun leaves while, as expressed on dry mass (Chl(m)), significant differences were only apparent in September, shade leaves presenting higher values. During the summer period Chl(a) and Chl(m) markedly declined in sun leaves and remained unchanged in shade ones. The ratio of chlorophyll a/b was not affected either by the light intensity or by the season. Shade leaves presented generally a higher concentration of soluble carbohydrates per dry mass. No significant differences in starch concentration were apparent between sun and shade leaves and a gradual depletion occurred during the water stress period. Maximum stomatal conductances correlated positively with predawn water potential. Throughout the season, sun plants always presented higher leaf conductance to water vapour and lower minimum leaf water potentials, indicating an interaction of light-environment on these water relation parameters. Stomatal closure constitutes a mechanism to cope with diurnal and seasonal water deficits, sun plants presenting a more efficient control of water losses during water deficiency period. In addition, both sun and shade plants evidenced leaf osmotic adjustment ability in response to water stress, which was greater in sun ones.

Raunsgaardispermum lusitanicum gen. et sp. nov., a new seed with in situ pollen from the Early Cretaceous (probably Berriasian) of Portugal: Further support for the Bennettitales‐Erdtmanithecales‐Gnetales link

A new genus and species, Raunsgaardispermum lusitanicum, is described from the Bombarral formation, Early Cretaceous (probably Berriasian) of Portugal. The new taxon is based on small well‐preserved, lignitised seeds, about 1.2 – 2.1 mm long and 0.9 – 1.26 mm wide, ovoid to broadly elliptic in outline with a distinct pointed micropylar region. The seed wall is composed by a thin membranous integument extended apically into a long tubular micropyle. The integument is enclosed almost completely by an outer envelope except for a small circular opening for micropylar region. The outer envelope is bivalved and sclerenchymatous, ornamented by narrow longitudinal ridges. Papillae are present apically on the inner surface of the seed envelope adjacent to the micropylar tube. Monocolpate, tectate‐psilate‐punctate pollen grains, about 26 – 29 µm long and 14 – 16 µm wide, were observed in situ in the micropyle of one seed and on the outer surface of several others. The seeds show an interesting character combination of distinct ephedroid seed characters coupled with pollen characters of Bennettitales and Erdtmanithecales and add further evidence to the link between Bennettitales, Erdtmanithecales and Gnetales.

Fossil Kajanthus lusitanicus gen. et sp . nov. from Portugal: Floral evidence for Early Cretaceous Lardizabalaceae (Ranunculales, basal eudicot)

Abstract A new fossil flower, Kajanthus lusitanicus gen. et sp. nov, is described from the Early Cretaceous (late Aptian–early Albian) Chicalhão site near the village of Juncal, western Portugal, based on a single coalified specimen. The flower is small, actinomorphic, trimerous and bisexual, slightly compressed and with floral organs tightly adhering. The perianth is organised in more than two whorls. The inner two whorls consist of six bulky, apparently fleshy parts. The outer perianth whorls consist of narrow parts. There are six stamens, arranged in two whorls. The filaments are thick and anthers tetrasporangiate. The pollen sacs are protruding with extrorse dehiscence. Pollen observed in situ is tricolpate, tectate, finely punctate-perforate, compressed and more or less spherical in polar view with a diameter of about 15 µm. The gynoecium is superior and composed of three free carpels. Non-destructive virtual sectioning of the single flower using synchrotron radiation X-ray tomographic microscopy revealed the presence of several curved ovules in each carpel, arranged in two longitudinal rows on marginal placentae. The character suite of the Kajanthus flower is only found in extant Lardizabalaceae (Ranunculales), where it is particularly close to Sinofranchetia, a monotypic genus that is now endemic to China.

Canrightiopsis, a new Early Cretaceous fossil with Clavatipollenites type pollen bridge the gap between extinct Canrightia and extant Chloranthaceae

Abstract Canrightiopsis with three species (C. intermedia, C. crassitesta, C. dinisii) is described from the Early Cretaceous of Portugal based on small, one-seeded berries. The fruits are derived from bisexual flowers with three stamens borne on one side of the ovary. There are no traces of a perianth. Pollen is of the Clavatipollenites-type, monocolpate, semitectate, reticulate-columellate with heterobrochate reticulum and muri with beaded supratectal ornamentation. The ovary is unilocular with a single pendant, orthotropous and bitegmic ovule. The seed is endotestal. The endotesta consists of one layer of palisade-shaped crystal cells with fibrous infillings. The fruit wall has resin bodies or cavities from presumed ethereal oil cells sometimes seen as stomata-like structures on the fruit surface. A phylogenetic analysis resolves Canrightiopsis as a close relative of extant Chloranthaceae, particularly close to extant Chloranthus and Sarcandra. All three taxa share the one-sided position of the stamens on the ovary. An evolutionary sequence from fossil Canrightia to fossil Canrightiopsis and extant Chloranthus and Sarcandra is suggested by loss of perianth, reduction in number of ovules and stamens and displacement of stamens to one side of the ovary. Canrightiopsis also shares several critical features with extant Ascarina including monoaperturate pollen and beaded supratectal ornamentation of the pollen wall.

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

Abstract 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.

A new species of the spore genus Costatoperforosporites from Early Cretaceous deposits in Portugal and its taxonomic and palaeoenvironmental significance

Abstract A new species of spore, Costatoperforosporites friisiae sp. nov., is described from the Early Cretaceous (late Aptian–early Albian) deposits of Catefica in the Lusitanian Basin, western Portugal. Although the morphology of the muri is clearly of the Cicatricosisporites type, the presence of micropores on these sculptural elements and within the intervening grooves is a particularly distinctive feature and more typical of spores that have been attributed previously to Costatoperforosporites. As a result, this genus is emended not only to accommodate Costatoperforosporites friisiae but also to differentiate it more clearly from other, similar, murornate genera. It is considered to represent the family Anemiaceae. So far, Costatoperforosporites friisiae has only been encountered in the Catefica palynoflora. The presence of many other pteridophyte spores, especially of schizaealean derivation, together with abundant cheirolepidiacean remains at this locality, strongly suggests a warm, moist climate and diverse source vegetation.

Paisia, an Early Cretaceous eudicot angiosperm flower with pantoporate pollen from Portugal

Abstract A new fossil angiosperm, Paisia pantoporata, is described from the Early Cretaceous Catefica mesofossil flora, Portugal, based on coalified floral buds, flowers and isolated floral structures. The flowers are actinomorphic and structurally bisexual with a single whorl of five fleshy tepals, a single whorl of five stamens and a single whorl of five carpels. Tepals, stamens and carpels are opposite, arranged on the same radii and tepals are involute at the base clasping the stamens. Stamens have a massive filament that grades without a joint into the anther. The anthers are dithecate and tetrasporangiate with extensive connective tissue between the tiny pollen sacs. Pollen grains are pantoporate and spiny. The carpels are free, apparently plicate, with many ovules borne in two rows along the ventral margins. Paisia pantoporata is the oldest known flower with pantoporate pollen. Similar pantoporate pollen was also recognised in the associated dispersed palynoflora. Paisia is interpreted as a possibly insect pollinated, herbaceous plant with low pollen production and low dispersal potential of the pollen. The systematic position of Paisia is uncertain and Paisia pantoporata most likely belongs to an extinct lineage. Pantoporate pollen occurs scattered among all major groups of angiosperms and a close match to the fossils has not been identified. The pentamerous floral organisation together with structure of stamen, pollen and carpel suggests a phylogenetic position close to the early diverging eudicot lineages, probably in the Ranunculales.

Clays and Vegetation: Comparing Palaeoclimatic Signatures in the Portuguese Lower Cretaceous

We collected a set of 120 clay samples with precise stratigraphic locations from the Lower Cretaceous coastal outcrops of the Ericeira area (western Portugal). The kaolinite versus illite dominance can be considered as revealing wet or dry climates, respectively, prevailing in the watershed. Swelling clays are associated with seasonally dry climates. However, since hydrodynamics and rejuvenation events also control clay associations, the relative role of climate versus depositional setting is still to be fully deciphered. As the onshore Lower Cretaceous of western Portugal is a key area for studying the Early Cretaceous initial diversification of angiosperms, several well-studied floras are summarized and their environmental interpretations presented.

Lower Cretaceous Pollen-Spore and Mesofossil Associations of the Bombarral Formation (Lusitanian Basin, Western Portugal)

The Lower Cretaceous of the Lusitanian Basin (western Portugal) contains rich assemblages of plant remains. The study of the palynological and mesofossil flora of the Berriasian Bombarral Formation in Vale Painho, near Juncal, contributes to ascertaining the environmental conditions during deposition, the vegetation diversity, and the unit’s age. The fossil site is just below the base of the Figueira da Foz Formation, a basin-wide breakup paraconformity. Regional correlation with biostratigraphically dated units (Lourinha p.p., Farta Pao, Porto da Calada, and Serreira) points to a Berriasian age for the top of the Bombarral Formation. The Vale Painho palynological assemblage is clearly dominated by fern spores and gymnosperm pollen. The mesofossil flora is characterized by seeds of conifers or taxa related to the Bennettitales– Erdtmanithecales–Gnetales (BEG) group, in agreement with palynomorphs. No angiosperm remains were recognized. The assemblage is very similar to the Berriasian to Valanginian Bornholm flora (Denmark). Plant features and sedimentary proxies indicate a hot climate with marked seasonality in precipitation.