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Cercidiphyllum and Fossil Allies: Morphological by Valentin Krassilov

By Valentin Krassilov

Cercidiphyllum is a relict angiosperm bringing to us a taste of Cretaceous interval. Its reproductive morphology used to be interpreted, within the spirit of the dominant evolutionary paradigm, as inflorescences of diminished flora represented by way of solitary pistils and teams of stamens. Evolutionary importance of Cercidiphyllum has lengthy been expected regardless of the unpersuasive morphological interpretation and inappropriate paleobotanical facts. This paintings was once firstly meant for paleobotanists who willingly evaluate their fossil fabric with the dwelling Cercidiphyllum, utilizing schematic descriptions and illustrations of conventional plant morphology. the assumption at the back of this e-book used to be to supply an properly 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, reminiscent of the substitute of the floral constitution by way of leafy shoots or the subtending bract-leaf conversion are appropriate to the experimental evo-devoA" stories and undergo on common difficulties of angiosperm evolution. In Cercidiphyllum, the vegetative physique is partially or in general produced within the reproductive line, suggesting a neotenic ancestral shape, within which the vegetative improvement used to be significantly diminished relative to reproductive area. Later in evolutionary historical past, the vegetative physique used to be rebuilt within the lineage so one can arboreal kinds, with foliation of the floral receptacles and the carpel-leaf convergence as unwanted effects of the method. Neoteny, or precocious fertility, may need required developmental equipment with ambivalent regulatory gene expressions within the foliar and floral primordia, invoking contrary evolutionary trends: (1) relief and removing 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. in regards to this version, the fossil list of Cercidiphyllum-like crops seems to be significant, even though nonetheless incomplete. The weedy Early Cretaceous ranunculids, together with kinds with a number of basal leaves, symbolize the neotenic degree, additionally recognizable within the evolution in their contemporaneous anthognetophytes. Transitional floral morphologies hyperlink such kinds to the later showing cercidiphyllids, platanoids and trochodendrocarpoids, the vegetative beneficial properties of which have been shaped on the subsequent, amplification level, represented by means of the Eocercidiphyllites plant from the mid- Cretaceous of the Negev, and have been conserved in the course of 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

Sample text

The giant stomata developing over blind veins acquire hydathode characteristics. Hydathodes strongly affect the patterning of ordinary stomata, which encircle the opening or spread in radial files away from it, an arrangement probably inflicted by the auxin maxima associated with hydathode formation (more on this in the discussion below). LEAF GLANDS A remarkable feature of Cercidiphyllum leaves is constant presence of marginal glands that are less conspicuous in mature leaves than in vernate leaves, including the leafy pherophylls.

Tiny stipulate leaves developing in the position of subtending bracts are observed in bud and are more frequent in C. 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 ...

2). Cercidiphyllum and Fossil Allies: Morphological Interpretation and General Problems ... 37 a b 100 µm c 100 µm d 50 µm e 50 µm f 20 µm 20 µm Fig. 14. Cercidiphyllum japonicum Sieb. , MSU: a, blind vein network; b, blind veins with hydathodes on ends; c, d, stomatal patterns relative to small veins; 5, 6, stomata-like hydathode openings. 38 Valentin Krassilov FLORAL STRUCTURES In view of their controversial interpretations in Cercidiphyllum, “flower” and “inflorescence” are here avoided as descriptive terms, and a neutral designation “floral structure” is used for the pistillate and staminate fascicles with their subtending bracts.

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