Life on Lan6 - Gnetum has leaves that look remarkably like...

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Life on Land The flowering plants most likely evolved from a Mesozoic gymnosperm group. At one time the cycadeoids were the prime candidates, although more recent studies suggest another group, the gnetophytes as the sister group to the angiosperms. Three distinctive genera comprise this group: Welwitschia , Gnetum , and Ephedra . Ephedra occurs in the western United States where it has the common name "Mormon tea". It is a natural source for the chemical ephedrine, although there is no evidence the Mormons in Utah (where the plant is extremely common) ever used it for tea, the use of stimulants being against their beliefs. Welwitschia is limited to coastal deserts in South Africa, although fossil leaf, cuticle and pollen evidence indicates plants of this type were widespread during the Mesozoic era. Welwitschia is noted for its two long, prominent leaves.
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Unformatted text preview: Gnetum has leaves that look remarkably like those in angiosperms, as well as vessels in the xylem , generally considered an angiosperm characteristic. Gnetophytes appear in the fossil record before the angiosperms do, and share a great many derived characteristics, making them the current choice as the angiosperm sister group (or ancestral group in a noncladistic sense). The angiosperms underwent an adaptive radiation during the Cretaceous, and for the most part escaped the major extinctions at the end of the Cretaceous. One group of angiosperms that did suffer from the extinction was the unknown groups of plants that produced triprojectate pollen. My dissertation dealt with the systematics of this fossil group. The pollen is quite odd-shaped and quite striking to see....
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This note was uploaded on 11/29/2011 for the course BIO BSC1010 taught by Professor Gwenhauner during the Fall '10 term at Broward College.

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