The helical arrangement of seed cone scales occurs among about 22% of the more than 3200 seed cones surveyed. The immature pollen grains have ontogenetic developmental significance, indicating that the spinulate processes of the mature Metasequoia pollen are probably developed from smooth gemmae. The fossil pollen in situ were explained as relatively immature due to only being extracted from the smaller pollen cones and having distinct morphology and anatomy under scanning and transmission electron microscopy. The foliar cuticles of the Arctic fossil were compared with those from the populations representing all the natural distribution areas of Metasequoia in central China and the result demonstrates that the fossil shares morphological resemblance most closely to those of the extant Metasequoia from an isolated population in central China’s Hunan Province, about 100 km southeast of the type locality in Hubei Province, central China. ![]() ![]() milleri), smaller pollen grains, gemmate exine but with more or less smooth gemmae, and seed cones with, in part, helically arranged scales in the fossil Metasequoia. Slight differences from the extant species, however, have been found, such as narrower stomatal bands, smaller stomata, higher stomatal density, presence of hypodermis (like that of M. A comparison with extant and previously published fossil Metasequoia is made in detail and indicates a morphological stasis since Late Cretaceous/Paleocene. The most significant systematic emendation made is the morphology of pollen and arrangement pattern of seed cone scales. An emendation is made on the basis of detailed description of the associated leaf-bearing branchlets, leaves, pollen cones, pollen in situ, and seed cones, particularly the presence of helically arranged scales in some seed cones, which is a feature no longer represented in the extant Metasequoia. occidentalis (Newberry) Chaney with an emendation, which is proposed to accommodate all the published Metasequoia fossils but M. A large number of fossilized remains, consisting of leafy branchlets, seed cones, pollen cones, and seeds, of Metasequoia (Cupressaceae) recovered from Middle Eocene sediments of the Buchanan Lake Formation, Axel Heiberg Island, Canadian Arctic Archipelago are studied morphologically and anatomically.
0 Comments
Leave a Reply. |