Abstract
Studies on Tracheary Element of Several Native Cycad Species in Australia and Two American Plants
Highlights
Cycads are very primitive seed plants of ancient; they originated from about the Carboniferous period [1], and still possess primitive characteristics in external morphology and internal structure, such as sperm with flagella
The scale of diameter of Cycas vessel element is similar to that of Zamia, but the diameter of more vessel elements of Cycas angulata and Cycas conferta is bigger than the latter, and is bigger than that of Guaiacum officinale, Cycas plants are more primitive than Zamia plants, and Guaiacum officinale is more evolutionary, but the scale of vessel diameter of Cycas plants is similar to Zamia or bigger than the latter, even larger than Guaiacum officinale, these showed that cycads have evolutionary and more developed characteristics in aqueous solution transport system
Analyzed from the structural characteristics, they distributed so far apart from each other, they are a well and unified taxonomy system; we thought that Australia’ most species or all species of Cycadaceae came from Asia, and it is impossible from Africa, because the latter only has one more evolutionary species and lack of fossil of Cycadaceae, these species of Cycadaceae are the descendants of ancestor species; America possessed more genera of Zamiaceae, this family is mutual with Africa and Australia, we thought that these genera of Zamiaceae in Australia and America came from Pangea before continental drift in Jurassic Period, this family is maybe one of the proofs to Australia drifted from Pangea to present position after Jurassic Period
Summary
Cycads are very primitive seed plants of ancient; they originated from about the Carboniferous period [1], and still possess primitive characteristics in external morphology and internal structure, such as sperm with flagella. Research on more species of cycad structural characteristics of tracheary elements is important to understand their adapted mechanism and evolutional extent. Huang et al [7] reported the structural feature of vessels on four genera of cycads and some angiosperms; Huang et al [8] published the structural characteristics of vessels in three families of Cycadopsida, Huang et al reported the structural characteristics of vessels of some gymnosperms and angiosperms [9]
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