By Valentin Krassilov

ISBN-10: 9546425249

ISBN-13: 9789546425249

Cercidiphyllum is a relict angiosperm bringing to us a style of Cretaceous interval. Its reproductive morphology used to be interpreted, within the spirit of the dominant evolutionary paradigm, as inflorescences of diminished flora represented through solitary pistils and teams of stamens. Evolutionary value of Cercidiphyllum has lengthy been expected regardless of the unpersuasive morphological interpretation and inappropriate paleobotanical proof. This paintings was once before everything meant for paleobotanists who willingly evaluate their fossil fabric with the residing Cercidiphyllum, utilizing schematic descriptions and illustrations of conventional plant morphology. the belief in the back of this publication was once to supply an correctly illustrated fabric for such comparisons. but it became out that there are extra issues in Cercidiphyllum than are dreamed of in our conventional plant morphology. a few of morphological findings of this examine, equivalent to the alternative of the floral constitution by way of leafy shoots or the subtending bract-leaf conversion are proper to the experimental evo-devoA" reports and undergo on basic difficulties of angiosperm evolution. In Cercidiphyllum, the vegetative physique is partially or more often than not produced within the reproductive line, suggesting a neotenic ancestral shape, within which the vegetative improvement used to be tremendously lowered relative to reproductive area. Later in evolutionary historical past, the vegetative physique was once rebuilt within the lineage to be able to arboreal types, with foliation of the floral receptacles and the carpel-leaf convergence as unwanted effects of the method. Neoteny, or precocious fertility, may have required developmental equipment with ambivalent regulatory gene expressions within the foliar and floral primordia, invoking contrary evolutionary traits: (1) aid and removal of sterile organs from the apical quarter and (2) secondary foliation of floral buildings. The ambiguous floral morphology of Cercidiphyllum is right here interpreted as a long-standing stability of those conflicting trends. with reference to this version, the fossil checklist of Cercidiphyllum-like crops seems significant, even supposing nonetheless incomplete. The weedy Early Cretaceous ranunculids, together with types with a couple of basal leaves, signify the neotenic degree, additionally recognizable within the evolution in their contemporaneous anthognetophytes. Transitional floral morphologies hyperlink such types to the later showing cercidiphyllids, platanoids and trochodendrocarpoids, the vegetative positive factors of which have been shaped on the subsequent, amplification degree, represented by means of the Eocercidiphyllites plant from the mid- Cretaceous of the Negev, and have been conserved throughout the later evolutionary advancements.

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Additional resources for Cercidiphyllum and Fossil Allies: Morphological Interpretation and General Problems of Plant Evolution and Development

Example text

The dorsal margin is nearly straight, with a shallow concavity above the seed body, thickened along the chalazal lobe, irregularly undulate along the micropylar lobe. The seed body is elliptical, nearly straight or only slightly curved, more convex on the lower (originally ventral) side, with a circular chalazal cap and a shortly protruding micropyle. It is turned obliquely to the long axis of the encircling wing, gently inclined or nearly parallel to the hilar scar, the micropyle pointing to the front lobe and slightly reflexed.

The ripe seeds are samaras with a bilobed orbicular wing. Raphe loops over the posterior lobe sending a short arm to the wing extremity. In addition to the reproductive structure – leafy shoot conversion, there are incidents of naturally occurring subtending bract – leaf and carpel – leaf conversions, evolutionary significance of which will be discussed after description of fossil allies. Cercidiphyllum and Fossil Allies: Morphological Interpretation and General Problems ... 59 6. FOSSIL ALLIES Reniform serrate leaves are widespread fossils since the Late Cretaceous.

Magnificum from Kew than in the sampled trees from the other places. They are recognizable by a prominent leaf blade, which is relatively thick, involute, and shows a conspicuous apical gland or also a few smaller subapical glands. The stipules are membranous, varying in shape and distinctness from Cercidiphyllum and Fossil Allies: Morphological Interpretation and General Problems ... 51 small outgrowths at the base of the blade to the broadly flared lobes, dentate and considerably larger than the blade.

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Cercidiphyllum and Fossil Allies: Morphological Interpretation and General Problems of Plant Evolution and Development by Valentin Krassilov

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