Presentation on theme: "BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008"— Presentation transcript:
1BIOLOGY 3404F EVOLUTION OF PLANTS Fall 2008 Lecture 17Thursday November 20, 2008Chapters 19 & 20, partsAngiosperm life cycle and flowers
2Angiosperm life cycleSimilar to gymnosperms, EXCEPT that the nuclear state of the developing ovule is much more complex:2n meiosis n mitosis 8 haploid nuclei (1 egg, 2 synergids, 3 antipodals, 2 polar nuclei)Double fertilization: 2 sperm nuclei involved, one fertilizing the egg ( 2n zygote) and one uniting with the 2 polar nuclei ( 3n endosperm) [other patterns exist, as in lilies]Food reserves of gymnosperm seeds are haploid (megagametophyte tissues); in angiosperms, they are triploid (endosperm) [5n in lilies]
10Seed of a eu-dicot, shepherd’s purse, with very little endosperm
11Angiosperm flowersFloral diversity is the hallmark of the angiosperms: how we recognize them and how they find (or are found) and recognize each other for mating purposesSelective forces for pollination, protection from predation, and eventual dispersal of seeds or fruits have shaped flowers and inflorescences
12A honeybee on Lemna (larger ovals) and two species of Wolffia (the smaller ones) (Fig. 21-2a). These are the smallest flowering plants.
13Wolffia borealis: whole flowering plant is less than 1 mm long
14Lemna gibba: flowering plant with two stamens and one style
60Foxglove (Digitalis, Scrophulariaceae) has a landing pad and “honey guides” for bee pollinators
61Marsh marigold (Caltha palustris, Ranunculaceae): what WE see
62Marsh marigold (Caltha palustris, Ranunculaceae): what BEES see
63A bumblebee in a California poppy (Eschscholzia californica, Papaveraceae)
64The “bee orchid” (Ophrys speculum, Orchidaceae) flower looks so much like a female bee that male bees try to mate with it; in doing so they get hit on the head or back with a pollen-sac, or pollinium, which they carry to the next flower
65A fly-pollinated orchid (Piperia elegans, Orchidaceae, left), and a mosquito carrying a dumbbell-shaped pollinium on its head (below)
66A fly on a camas lily (Zygadenus) with bright yellow nectaries
67Many butterflies and moths are pollinators, and drink nectar through their long proboscis (arrow)
68A yucca moth on a Yucca flower (Asparagaceae); larval moths eat some of the seeds in the resulting yucca fruit
69Bird-pollinated flowers are often red; those pollinated by hummingbirds usually have a long corolla tube with nectaries at the bottom. Note anthers dusting the bird’s forehead with pollen.
70A sunbird (Anthreptes) at a bird-of-paradise flower (Strelitzia, Strelitziaceae). Sunbirds are regarded as important pollinators, but this one appears to be taking the “nectar thief” shortcut through the bottom of the flower.
71The nectar of these columbine flowers is only (?) available to birds
72Poinsettias (Euphorbia pulcherrima, Euphorbiaceae) are pollinated by birds, but ants like the nectar, too.
73A lesser long-nosed bat (Leptonycteris curasoae) getting a faceful of pollen at a cactus flower at night.
74Threadlike pollen of the sea-nymph (Amphibolis, Cymodoceaceae, Alismatales) trapped on the forked stigma. Whereas most aquatic plants actually have aerial flowers and “normal” pollination, those whose pollination is truly aquatic often have filamentous pollen.
75Staminate flowers (left) of the freshwater eel-grass (Valisneria, Hydrocharitaceae) are produced underwater, then are released to float to the surface. There, they drift into depressions formed by the larger pistillate flowers, which remain attached to the plant.
76Pollinators and floral diversity Plants with catkins (slides 34 and 35) are mostly wind-pollinated, as are the grasses and most gymnosperms.Were pollinators the only forces shaping flowers through evolutionary history? See the paper by Brown (2002), linked on the web site.