Welwitschiaceae from the Lower Cretaceous of northeastern Brazil

Dilcher, David L.; Bernardes-de-Oliveira, Mary Elizabeth Cerruti; Pons, Denise; Lott, Terry A.

doi:10.3732/ajb.92.8.1294

Cited by 102 publications

(81 citation statements)

References 51 publications

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“…The presence of Ephedra and of Welwitschiaceae during the Early Cretaceous has been confirmed recently by evidence from megafossils (e.g. Rydin et al 2004Rydin et al , 2006Dilcher et al 2005).…”

Section: Gnetalesmentioning

confidence: 74%

“…Srivastava, 1968 and references therein), while the famous Welwitschia with the only living species Welwitschia mirabilis is restricted to deserts along the southwestern coast of Africa (Dilcher et al 2005). Therefore Ephedra-and Welwitschia-like pollen may be regarded as indicative of semi-arid to arid conditions although a wider range of ecological adaptations has been envisaged for their fossil counterparts (Srivastava 1968;Dilcher et al 2005).…”

Section: Gnetalesmentioning

confidence: 99%

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Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications

Schrank

2010

Palynology

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Two informal sporomorph assemblage zones can be distinguished in the dinosaur-bearing Tendaguru Beds of southeast Tanzanian. The first zone, the Classopollis-Araucariacites-Shanbeipollenites Assemblage Zone, ranges from the Lower to the Upper Saurian Bed, and a mid-Oxfordian to Tithonian age is suggested based on the presence of Shanbeipollenites quadratus. The second zone, the Classopollis-Cicatricosisporites-Ruffordiaspora Assemblage Zone, is restricted in the Trigonia schwarzi Bed, which overlies the Upper Saurian Bed. The combined ranges of Cicatricosisporites hughesii, Ruffordiaspora australiensis and Trilobosporites obsitus would be consistent with a late Berriasian to Hauterivian age of this zone. This is refined further to late Valanginian to Hauterivian on the basis of already existing evidence from fauna and dinoflagellate cysts. From a phytogeographic point of view the Tendaguru locality belongs to the southern Gondwana Trisaccates Province because of the presence of trisaccate podocarpaceous pollen. The quantitative composition of the palynofloras is characterized by the dominance or abundance of pollen produced by the two conifer families Cheirolepidiaceae (Classopollis) and Araucariaceae (mainly Araucariacites). Pollen of Cheirolepidiaceae, typically xerophytic, drought-resistant, thermophilic plants, is dominant throughout the Tendaguru Beds except in parts of the Middle Saurian Bed where pollen of Araucariaceae, a presumably mesic group, becomes most abundant. Classopollis attains the highest degree of dominance in the shallow marine deposits associated with the saurian beds. This may be related to paleoecological and taphonomic factors, namely abundance of Classopollis-producing plants in low-lying coastal environments close to the lagoonlike depositional sites and transportational sorting of sporomorphs leading to a relative enrichment of small and/or anemophilous pollen. The abundance of Araucariacites in the Middle Saurian Bed suggests that araucarians existed in coastal plain environments that were stable enough to allow the growth of large trees. This open araucarian forest, which may have been a source of food for high-browsing dinosaurs, was situated landward of the cheirolepidiacean belt not far from the depositional sites. Pteridophytes and bryophytes were concentrated at moist places and around water bodies. Podocarpaceous conifers producing bisaccate and trisaccate pollen grew in local uplands, while gnetaleans related to Ephedra and Welwitschia may have been present in dry places. The palynological evidence is consistent with a seasonally dry, tropical to sub-tropical paleoclimate. Three new combinations, Equisetosporites certus (Bolkhovitina), Jugella caichigu¨ensis (Volkheimer and Quattrocchio) and Trichotomosulcites microsaccatus (Couper), are proposed, and Jugella semistriata is described as a new species.

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Section: Gnetalesmentioning

confidence: 74%

Section: Gnetalesmentioning

confidence: 99%

Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications

Schrank

2010

Palynology

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“…The vegetative distinctions between these genera are familiar to most botanists. Gnetales have a relatively long fossil history; the three genera were already distinct in the lower Cretaceous (Dilcher et al 2005;Rydin et al 2006;Yang 2010). Gnetalean (ribbed) pollen grains have been found in sediments as old as the Triassic, but probable macrofossils also date from Permian times (Crane 1996;Wang 2004).…”

Section: Introductionmentioning

confidence: 99%

Wood Anatomy of Gnetales in a Functional, Ecological, and Evolutionary Context

Carlquist¹

2012

aliso

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New scanning electron microscope (SEM) and light microscope data and illustrations are presented in order to compare hydraulic adaptations of non-gnetalean conifers and angiosperms to relevant wood features of Gnetales. Gnetales have essentially all of the adaptations of both groups, yet have not competed well, despite predating angiosperms in origin and radiation. Angiosperms may be advantaged more by life cycle abbreviation and by heterochronic possibilities than by wood features. Wood features of Gnetales that relate to conduction (torus-margo differentiation of tracheid pit membranes, distribution of tori within the wood, perforation plate simplification, growth rings, vesturing, helical thickenings, and axial parenchyma) are reviewed in the light of recent work that demonstrates the physiological significance of these features in angiosperms. The various xylary adaptations of Ephedra, Gnetum, and Welwitschia are analyzed in terms of conductive efficiency versus conductive safety, and in turn, compared to the habitats of the three genera, respectively: Ephedra and Welwitschia survive in rather extreme habitats, whereas Gnetum competes in mesic forest by what may be minor shifts among basically similar niches. Gnetales have essentially all of the wood anatomical advantages of angiosperms, except for ability to shift degrees of wood anatomical juvenilism or adulthood-an important angiosperm advantage. The relatively lengthy life cycle of Gnetales, requiring female gametophyte formation prior to embryo formation (vs. simultaneous endosperm and embryo development in angiosperms) and the related requirement for at least several years' growth prior to seed formation are probably the prime reasons for lack of gnetalean success. Wood features should be interpreted as adapted to the present-day ecology of a woody species, and ideas that evolutionary flexibility to shift into more seasonal conditions is hindered by rigid wood formulas (which actually can change rather rapidly) should be questioned. Wood evolution of Gnetales, like that of angiosperms, can be regarded as a series of shifts in the trade-offs between conductive efficiency and conductive safety.

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“…A similar structure occurs in a Cre taceous fossil seedling of a plant closely related to Welwit schia (Rydin et al 2003). Conversely, Dilcher et al (2005) ques tioned the cotyledon homologies proposed by Rydin et al, and did not report a feeder in seedlings of another fos sil related to Welwitschia. The cotyledons of Gnetum and Welwitschia do not act as haustoria on germination.…”

Section: Scenario 1: Seedlings Of Gnetales Retained Plesiomorphic Feamentioning

confidence: 86%

Functional Aspects of the Origin and Subsequent Evolution of Cotyledons in Seed Plants

Sokoloff¹,

Rudall²,

Bateman³

et al. 2015

Bot Pac

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In most seed plants, cotyledons formed within the seed act as haustorial organs, as well as playing a key role in releasing the shoot apex from the seed coat on germination. Emergence of the shoot apex often results from asymmetric intercalary growth of the cotyledon bases. This process avoids the principal spatial constraint on germination in seed plants, wherein the plumule is surrounded by cotyledons whose tips should be in contact with nutritive tissues. Cotyledons are commonly viewed as a synapomorphy of the seed-plant lineage and as the modified first leaves of a seedling. However, intercalary growth, which is crucial for the cotyledon's role in releasing the plumule, had not yet been acquired by foliage leaves of the earliest seed plants. We explore the possibility that the program of intercalary growth in leaves first evolved in cotyledons and was subsequently recruited for foliage leaves in the seed-plant lineage. We also discuss whether early seed plants already possessed haustorial cotyledons. Семядоли большинства семенных растений выполняют гаустори-альные функции, а также играют важную роль в высвобождении апекса побега из семени при его прорастании. Высвобождение апекса побега часто идет за счет асимметричного интеркалярного роста оснований семядолей. Этот про-цесс позволяет обойти ключевое пространственное ограничение при прорас-тании семенных растений, связанное с тем, что почечка окружена семядоля-ми, верхушки которых связаны с питательными тканями семени. Семядоли обычно считают синапоморфией семенных растений и видоизмененными первыми листьями проростка. Однако интеркалярный рост, столь важный для роли семядолей в высвобождении почечки, еще не был приобретен листья-ми древнейших семенных растений. Из-за отсутствия прямых свидетельств мы обсуждаем четыре гипотетически возможных сценария происхождения семя-долей. Мы рассматриваем возможность того, что интеркалярный рост впервые появился у семядолей, а затем эта программа развития распространилась и на обычные листья семенных растений. С другой стороны, возможно, что древ-нейшие семенные растения еще не имели гаусториальных семядолей.Ключевые слова: гаусторий, голосеменные растения, интеркалярный рост, ме-гафилл, прорастание семени, пространственное ограничение, развитие зародыша

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Welwitschiaceae from the Lower Cretaceous of northeastern Brazil

Cited by 102 publications

References 51 publications

Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications

Pollen and spores from the Tendaguru Beds, Upper Jurassic and Lower Cretaceous of southeast Tanzania: palynostratigraphical and paleoecological implications

Wood Anatomy of Gnetales in a Functional, Ecological, and Evolutionary Context

Functional Aspects of the Origin and Subsequent Evolution of Cotyledons in Seed Plants

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