19_Maloof_Gymnosperms_Outline

19_Maloof_Gymnosperms_Outline - Lecture 19 / Plant Lecture...

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Unformatted text preview: Lecture 19 / Plant Lecture 6: Gymnosperms 1) Life cycle review and clicker questions 2) Tour through the seed plants a) Angiosperms vs gymnosperms b) The seed plants are grouped into five clades I want to take a quick tour through the four gymnosperm clades c) Cycadophyta i) Look somewhat like palms (“Sago Palm”) ii) But true palms are monocot angiosperms. These are different, they make their seeds in cones. Look outside the lab building, near Storer Hall. iii) Were very abundant during the Mesozoic, 245-65 MYA…this is often called the “Age of Cycads and Dinosaurs” iv) Ovules and microsporangia on separate plants v) Insect pollinated, unusual for a gymnosperm. Long-standing relationship with weevils. Some species live in the male cones and visit female cones. d) Ginkgophyta i) In prehistoric times there were many species in this phyla ii) Now Ginkgo biloba—Only living species. iii) Beautiful tree, little changed for over 150 Million Years. iv) Often planted in urban setting because it is very tolerant of air pollution. v) Separate male and female trees. Donʼt plant the female tree because the seed coat smells horrible. vi) Leaves show an interesting pattern with dichotomously branched veins. vii)The leaves often split into two lobes…hence the epithet biloba viii) You may be familiar with Ginkgo biloba because the leaves are used as an herbal supplement which is reported to improve memory and mental sharpness. e) Coniferophyta i) Conifers: Spruce, Fir, Redwood, Pine, etc ii) Most diverse, widespread, ecologically and economically important gymnosperm today. iii) 10% of Worldʼs photosynthesis iv) 50 genera, 550 species v) Major source of wood and paper vi) Tallest living things (1) Coastal redwoods vii)Most massive living organisms: Giant Sequoia = 80M, 20002500 Metric Tons; compare Blue Whale = 35M, 180 Metric Tons viii) Oldest living Trees…Bristlecone pines…4900 years ix) Needles (1) specialized leaf (2) Typically very well suited for growth in arid conditions (3) Thick cuticle (4) sunken stomata (5) two vascular bundles enclosed in endodermis (6) transfusion tissue to transport from mesophyl cells to vascular bundles x) (Dawn redwood—living fossil—not discussed in 2005) f) Gnetophyta i) 3 Genera, 70 Species. (1) Gnetum: shrubs, trees, climbing vines. Dicot looking leaves (2) Ephedra: Profusely branching shrubs with small, scalelike leaves. A source of the drug ephedrine. (3) Welwitschia (a) Bizare. Mostly underground. Exposed is a massive concave disk that produces only two leaves. These leaves then split lengthwise with age, giving the appearance of many leaves. (b) Native to the desert in Namibia. An extremely dry area receiving ~ 2cm of rain per year. (c) Cone-bearing tissues arise from meristematic tissue at the edge of the disk. 3) Additional features seen in some seed plants a) Double fertilization b) Loss of swimming sperm (relate to pollination) c) Other gnetum hypotheses/characters d) Loss of archegonia e) Gnetum resemble the Angiosperms in many respects. This had led taxonomists to consider gnetophytes to be the closest living relatives of the angiosperms, but not it appears that these traits arose by convergent evolution. i) No Archegonia ii) Vessels and Fibers iii) Some strobili resemble inflorescences (flower clusters) iv) Double fertilization v) (The first two features are likely because of convergent evolution…) 4) ...
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This note was uploaded on 03/09/2011 for the course BIS 2 taught by Professor Coolprof during the Spring '11 term at Bank Street College of Education.

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