Academic literature on the topic 'Angiosperm'

The photosynthetic gas exchange capacities of early angiosperms remain enigmatic. Nevertheless, many hypotheses about the causes of early angiosperm success and how angiosperms influenced Mesozoic ecosystem function hinge on understanding the maximum capacity for early angiosperm metabolism. We applied structure-functional analyses of leaf veins and stomatal pore geometry to determine the hydraulic and diffusive gas exchange capacities of Early Cretaceous fossil leaves. All of the late Aptian—early Albian angiosperms measured possessed low vein density and low maximal stomatal pore area, indicating low leaf gas exchange capacities in comparison to modern ecologically dominant angiosperms. Gas exchange capacities for Early Cretaceous angiosperms were equivalent or lower than ferns and gymnosperms. Fossil leaf taxa from Aptian to Paleocene sediments previously identified as putative stem-lineages to Austrobaileyales and Chloranthales had the same gas exchange capacities and possibly leaf water relations of their living relatives. Our results provide fossil evidence for the hypothesis that high leaf gas exchange capacity is a derived feature of later angiosperm evolution. In addition, the leaf gas exchange functions of austrobaileyoid and chloranthoid fossils support the hypothesis that comparative research on the biology of living basal angiosperm lineages reveals genuine signals of Early Cretaceous angiosperm ecophysiology.

Angiosperm mesofossils are described from the Lower Cretaceous Almargem Formation exposed near the village of Catefica, Portugal, and are thought to be of Aptian-early Albian age. The mesofossil assemblage from Catefica is diverse and, in addition to the angiosperms described here, also contains a rich assemblage of non-angiosperm fossils, including leafy axes of bryophytes and lycopsids, lycopsid and salvinialean megaspores, and sporangia, sori and leaf fragments of ferns. There are also twigs, cones, cone scales, seeds and sporangia of several kinds of conifers. Other seed plants include 11 species of chlamydospermous seeds and vegetative axes related to the BEG group (Bennettiales-Erdtmanithecales-Gnetales). In terms of the number of plant fragments identified, angiosperms are most abundant in the Catefica assemblage and account for more than half of all specimens. Angiosperms also dominate in number of species, but because the non-angiosperm fossils have not been studied in detail the total number of species in the flora is not yet established. Sixty-seven species of angiosperms are recognized. Angiosperm diversity is mainly at the level of non-eudicots, including ANA-grade angiosperms, Chloranthaceae and magnoliids. Remains of chloranthoid angiosperms are especially common, both in the number of specimens and in number of species recognized. About 40 % of the specimens, and more than 25 % of the species are chloranthoids. Remains of magnoliid angiosperms (Magnoliales, Laurales, Canellales, Piperales) are also prominent among the angiosperms. Eudicots are subordinate: only 3–4 % of all angiosperm specimens can be assigned confidently to eudicot angiosperms. Five new genera and six new species of angiosperms are established (Canrightia foveolata sp. nov., Elasmostemon paisii gen. et sp. nov., Endressistemon cateficensis gen. et sp. nov., Ibericarpus cuneiformis gen. et sp. nov., Proencistemon portugallicus gen. et sp. nov., Valvidistemon globiferus gen. et sp. nov.). Several other new taxa are also described, but not formally named.

Molecular phylogenetic analyses have provided increasing evidence that angiosperms are not related to Gnetales, thus contradicting the anthophyte hypothesis based on morphological cladistic analyses and throwing the question of angiosperm relatives back to paleobotanists. Previous analyses of gene sequences based on a molecular clock conflicted with the fossil record in indicating a Late Palaeozoic or Triassic origin of the angiosperms, but closer examination suggests that these dates were biased by the use of herbaceous taxa with accelerated rates of molecular evolution. Despite uncertainty on angiosperm relatives, analyses of many genes consistently place Amborella, Nymphaeales, Austrobaileya, Trimenia and Illiciales (the ‘ANITA grade') at the base of extant angiosperms, possibly followed by Chloranthaceae. Molecular phylogenies imply that the first crown-group angiosperms had columellar exine structure, suggesting that Hauterivian-Barremian reticulate-columellar monosulcates may be closer to the origin of angiosperms than was thought when granular Magnoliales were believed to be basal. Hauterivian pollen with a verrucate tectum and microspinules is especially similar to Amborella. The ANITA lines and Chloranthaceae have ascidiate carpels sealed by secretion and often exotestal seeds, fitting the abundance of such carpels and seeds in Barremian-Aptian mesofloras. Similarities between Aptian angiosperm leaves and ANITA taxa, such as chloranthoid teeth and variable stomatal structure, also suggest that Early Cretaceous angiosperms were more primitive than previously appreciated. Molecular results may help refine search images for extinct angiosperm relatives, away from Gnetales and toward groups such as Caytonia, Glossopterids, Bennettitales and Corystosperms. Since molecular data place the vesselless taxa Amborella and Nymphaeales at the base of the angiosperms, the presence of vessels is not evidence that gigantopterids are related to angiosperms. The conclusion that columellar structure is ancestral reaffirms the potential of Triassic reticulate-columellar Crinopolles pollen as angiosperm relatives.

The hydraulic efficiency conferred by vessels is regarded as one of the key innovations explaining the historical rise of the angiosperms at the expense of the gymnosperms. Few studies, however, have compared the structure and function of xylem and their relationships with foliage traits in evergreen representatives of both groups. We measured sapwood cross-sectional area, conduit diameters, hydraulic conductance, and leaf area of fine branches (2.5–7.5 mm diameter) of five conifers and eight evergreen angiosperm trees in evergreen temperate forests in south-central Chile. Conductance of both lineages was higher at Los Lleuques, a warm temperate site with strong Mediterranean influence, than in a cool temperate rain forest at Puyehue. At a common sapwood cross-sectional area, angiosperm branches at both sites had greater hydraulic conductance (G) than conifers, but similar leaf areas. Branch conductance normalized by subtended leaf area (GL) at both sites was, therefore, higher in angiosperms than in conifers. Hydraulically weighted mean conduit diameters were much larger in angiosperms than in conifers, although this difference was less marked at Puyehue, the cooler of the two sites. Conduits of the vesselless rain forest angiosperm Drimys winteri J.R. & G. Forst were wider than those of coniferous associates, although narrower than angiosperm vessels. However, GL of D. winteri was within the range of values measured for vesselbearing angiosperms at the same site. The observed differences in xylem structure and function correlate with evidence that evergreen angiosperms have higher average stomatal conductance and photosynthetic capacity than their coniferous associates in southern temperate forests. Comparisons of conifers and angiosperm branches thus suggest that the superior capacity of angiosperm conduits is attributable to the development of higher gas-exchange rates per unit leaf area, rather than to a more extensive leaf area. Results also suggest that the tracheary elements of some vesselless angiosperms differ in width and hydraulic efficiency from conifer tracheids.

This paper reports the recent study of the earliest known angiosperms in the world found from the Lowe Cretaceous of Jixi, China, and first demonstrates the general information on the oldest known Inflorescences Xingxueina heilongfiangensis Sun et Dilcher (MS) contained in the Jixi early angiosperms. The inflorescences possess numerous pollens in situ, very small, inaperturate and tectate-columellate in exine, and can be compared to those from Valanginian-Hauterivian of Israel studied by Brenner (1995). Based on the comparison and on the marine beds, yielding Valanginian-Hauterivian dinoflagellates, underlying conformably the angiosperm-bearing beds the Jixi angiosperms are considered Hauterivian or Hauterivian-Early Barremian in age. The paper has also discussed the findings of the angiosperm-like or questionable angiosperm material newly from China and previously from Mongolia, proposed there might exist an original centre of angiosperms in East Asia. However, it would not be excluded that there were two original centres (East Asia and Eastern Gondwanaland) where the earliest angiosperms evolved and developed in parallel during the early time of Early Cretaceous.

Competitive interaction between conifers and angiosperms has moulded the structure of global vegetation since the Cretaceous. Angiosperms appear to enjoy their greatest advantage in the lowland tropics, an advantage often attributed to the presence of vessels in their xylem tissue. By monitoring the seedling growth of three members of the pan-tropical conifer family Podocarpaceae and three tropical angiosperm tree species, our aim was to determine whether these conifer and angiosperm seedlings showed distinct patterns of growth and light adaptation that might be attributed to the presence/absence of vessels. Angiosperm seedlings were consistently more efficient in terms of leaf area carried per unit stem investment, as well as more responsive to light climate than the conifer seedlings. Apparently linked to this were larger growth rate, stem hydraulic conductivity and stomatal conductance in the angiosperm sample. Stem hydraulic conductivity and maximum stomatal conductance were highly correlated among species and light treatments explaining the association between highly conductive vessel-bearing wood and high rates of gas exchange. We conclude that xylem vessels contribute to higher rates of gas exchange and more efficient production of leaf area in our sample angiosperms than in conifers. However, this advantage is limited by shade.

Abstract Several recent palaeobotanical studies claim to have found and described pre-Cretaceous angiosperm macrofossils. With rare exceptions, these papers fail to define a flower, do not acknowledge that fossils require character-based rather than group-based classification, do not explicitly state which morphological features would unambiguously identify a fossil as angiospermous, ignore the modern conceptual framework of phylogeny reconstruction, and infer features in the fossils in question that are interpreted differently by (or even invisible to) other researchers. This unfortunate situation is compounded by the relevant fossils being highly disarticulated two-dimensional compression-impressions lacking anatomical preservation. Given current evidence, all supposed pre-Cretaceous angiosperms are assignable to other major clades among the gymnosperms sensu lato. By any workable morphological definition, flowers are not confined to, and therefore cannot delimit, the angiosperm clade. More precisely defined character states that are potentially diagnostic of angiosperms must by definition originate on the phylogenetic branch that immediately precedes the angiosperm crown group. Although the most reliable candidates for diagnostic characters (triploid endosperm reflecting double fertilization, closed carpel, bitegmic ovule, and phloem companion cells) are rarely preserved and/or difficult to detect unambiguously, similar characters have occasionally been preserved in high-quality permineralized non-angiosperm fossils. The angiosperm radiation documented by Early Cretaceous fossils involves only lineages closely similar to extant taxonomic families, lacks obvious morphological gaps, and (as agreed by both the fossil record and molecular phylogenies) was relatively rapid—all features that suggest a primary radiation. It is unlikely that ancestors of the crown group common ancestor would have fulfilled a character-based definition of (and thereby required expansion of the concept of) an angiosperm; they would instead form a new element of the non-angiosperm members of the ‘anthophyte’ grade, competing with Caytonia to be viewed as morphologically determined sister group for angiosperms. Conclusions drawn from molecular phylogenetics should not be allowed to routinely constrain palaeobotanical inferences; reciprocal illumination between different categories of data offers greater explanatory power than immediately resorting to Grand Syntheses. The Jurassic angiosperm—essentially a product of molecular phylogenetics—may have become the holy grail of palaeobotany but it appears equally mythical.

Three alcohol dehydrogenase (ADH) cDNAs were isolated from Pinusradiata. Two of the cDNAs appear to correspond to alleles of one ADH locus, and the third cDNA appears to correspond to a second ADH locus. Nucleotide and amino acid sequences of the coding region of ADH genes from the following species were compared: Pinusradiata, Zeamays, Hordeumvulgare, Triticumaestivum, Oryza sativa, Pisumsativum, and Arabidopsisthaliana. A phylogenetic tree was constructed of coding sequences of pine and angiosperm ADH genes. This tree shows three plant ADH clusters: monocot, dicot, and pine. The distance between pine and the two angiosperms is only slightly greater than the distance between either angiosperm, supporting the fossil evidence that suggests that monocots and dicots diverged from each other shortly after angiosperms diverged from gymnosperms. The structure of pine ADH genes was investigated by Southern blot analysis. The restriction fragment pattern of ADH genes from pines is more complex than the pattern from angiosperm genes, suggesting that pine ADH genes are either larger or more numerous than their angiosperm counterparts.

Models of origin for the typical angiosperm leaf, flower, stamen, pistil and double fertilization are based on evolutionary trends in proangiosperms. It is suggested that angiosperm organs are of chimeric origin, acquired by aggregation and fusion of progenitorial structures. These morphological processes might involve different proangiosperm lineages in unstable (ecotonal, tectonically active) environments. An advantage of early angiosperms in such environments might be due to extended evolutionary potentials of their chimeric organs capable of acquiring new functions related to entomophily and zoochory.

Background: The origin and early evolution of angiosperms, by far the most important plant group for human beings, are questions demanding answers, mainly due to a lack of related fossils. The Yixian Formation (Lower Cretaceous) is famous for its fossils of early angiosperms, and several Early Cretaceous angiosperms with apocarpous gynoecia have been documented. However, a hypanthium and an inferior ovary are lacking in these fossil angiosperms. Methods: The specimen was collected from the outcrop of the Yixian Formation in Dawangzhangzi in the suburb of Lingyuan, Liaoning, China. The specimen was photographed using a Nikon D200 digital camera, and its details were photographed using a Nikon SMZ1500 stereomicroscope and a MAIA3 TESCAN SEM. Results: A fossil angiosperm, Lingyuananthus inexpectus gen. et sp. nov, is reported from the Lower Cretaceous of China. Differing from those documented previously, Lingyuananthus has a hypanthium, an inferior ovary, and ovules inside its ovary. Such a character assemblage indicates its angiospermous affinity, although not expected by any existing leading angiosperm evolutionary theory. Conclusions: New fossil material with a unique character assemblage falls beyond the expectation of the currently widely accepted theories of angiosperm evolution. Together with independently documented fossils of early angiosperms, Lingyuananthus suggests that at least some early angiosperms’ flowers can be derived in a way that has been ignored previously.