Botany Lecture (12/7)

Angiosperms: The Flowering Plants Diversity in Phylum Anthophyta The Flower (structure) He Angiosperm Life Cycle Evolution of the Flower& Fruit (function) Review: Extant seed plants Gymnosperms Cycads, Ginkgo, Conifers, Gnetophytes Angiosperms: greater than 250,000 species!! Still continued to be discovered to this day A really dominant group Angiosperms (alternate name for Phylum Anthophyta) Number of feature that define a flowering plant Xylem with tracheids & vessels Flowers (the flowering plants) Ovules protected within carpels (=ovary) Ovary matures into a fruit (=container with seeds inside) Reduced gametophytes No archegonia (single cell represents the egg, not held within sex organ) Pollen tube, non-motile sperm Double fertilization Endosperm Angio= ?a vessel, receptacle or container? Not naked seeds, ovules are held within a container for even greater protection Ovary- after its fertilized= fruit Do not know how flowering plants evolved; almost no fossil evidence 1. Xylem- tracheids and vessels Tracheids- to pass water through the plant Small tracheids with very large vessels 2. Flower Attracts pollinators to the plant Determinate: reproductive shoots (when a flower is initiated during development, that?s it, the shoot will be determined, the size of the shoot stops) Four whorls (typically) of modified sterile leaves and sporophylls (four whorls= sepal, petal, stamen, carpel) Sepal Petal Stamen: (male side) microsporophyll with four microsporangia, producing microspores Carpel: (female) megasporophyll enclosing the ovules Where did the flower come from? New fossil discoveries from north China- one of them that has caught people attention in the last few years= 125 mya called Archaefructus Doesn?t look like its producing flowers, but there are carpels and stamens (but plant is lacking petals and sepals) Scientists believe it is an aquatic plant (didn?t need petals and sepals) Does this represent the most primitive flowering plant? Parts of the flower: Outer whorl= sepals- 3 leafy like structures; collectively all sepals of the flower are called the calyx Function- help to protect young reproductive structures while flower is developing Next whorl (usually colorful)- 3 petals; collectively the petals together= corolla Function- advertisment; lure to insects (pollinators to the flower) Perianth= calyx and corolla (parts that go around the flower) These are sterile- not involved in the life cycle 3rd whorl represents the androecium (ecium= house and andro= male Consists of the stamen- made up of a filament and anther Anther sits on a filament (long filament with anther on top producing pollen= stamen) Evolution of the stamen- some plants have a very broad stamen and sporangia are sitting flat on structure (pic 2) Anther- a cross section through the Lily anther- see four sporangia (micro); within these are where meiosis occurs Tetrad of microspores following meiosis (1 to 4; diploid to haploid) 4th whorl= carpel (female ? in the center of the flower)- Gynoecium Composed of carpels- which are made up of a swollen basal area= ovary, and then a more elongated= style, and very tip of style= stigma) Within the ovary are where the ovules are held- which with ultimately produce the seeds Very common for carpels to fuse together= pistil; essentially the same thing Evolution of the carpel Some kind of gymnosperm that produces a megasporophyll with ovules on the margin of the leaf; perhaps this leaf folded in half (to protect the ovules) and then fusing margin of that folded leaf= complex carpel we see today Syncarpous- carpels are fused Apocarpus- separate carpels If the flower has all four whorls= perfect and complete (all four whorls + male and female) A complete (all four must have male and female) flower must be perfect, and an imperfect flower, by definition, is incomplete, but not all incomplete flowers are imperfect. How many carpels comprise these ovaries? a)3, syncarpous= fusion of three separate carpels Life Cycle Males- Mature microgametophyte (pollen) has only 3 nuclei- a division takes place (2 nuclei where one of them= tube= responsible for germination, controlling pollen tube and reach the female and the second nuclei is called the generative cell= going to divide to produce two sperm) Female- Pistal= composed of 3 carpels Ovary= 6 young ovules, expand (enlarge) one of those= a single cell which is the megaspore mother cell- she will undergo meiosis Megagametophyte is reduced to just 8 nuclei (common name= 7 celled ?embryo sac?) 1 egg cell- surrounded by synergids (=3 cells), 3 more move to opposite pole of ovule called antipodals (=3 more), 2 remaining nuclei sit in the center= polar nuclei