BIOLOGY 3404FEVOLUTION OF PLANTS

Fall 2008

Lecture 17Thursday November 20, 2008Chapters 19 & 20, parts

Angiosperm life cycle and flowers

Angiosperm life cycle• Similar 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]

Corn seed, with lots of endosperm

Seed of a eu-dicot, shepherd’s purse, with very little endosperm

Angiosperm flowers

• Floral diversity is the hallmark of the angiosperms: how we recognize them and how they find (or are found) and recognize each other for mating purposes

• Selective forces for pollination, protection from predation, and eventual dispersal of seeds or fruits have shaped flowers and inflorescences

A honeybee on Lemna (larger ovals) and two species of Wolffia (the smaller ones) (Fig. 21-2a). These are the smallest flowering plants.

Wolffia borealis: whole flowering plant is less than 1 mm long

Lemna gibba: flowering plant with two stamens and one style

Coconut palm, Cocos nucifera

Flowers and fruits of banana (Musa x paradisiaca)

Rice (Oryza sativa)

Saguaro cactus in flower

An orchid flower (Cattleya)

An orchid flower (l) compared to a radially symmetrical flower (r)

Parts of a lily flower

Hepatica americana (Ranunculaceae, a basal eudicot)

California poppies

Types of inflorescences (arrangements of flowers). I

Types of inflorescences (arrangements of flowers). II

Types of inflorescences (arrangements of flowers). III

Types of inflorescences (arrangements of flowers). IV

Shooting star (Dodecatheon)

Butter-and-eggs (Linaria vulgaris)

Lupine (Lupinus)

Mertensia

Water hemlock (Cicuta maculata)

A catkin, of birch (Betulaceae)

Staminate catkins and acorns of tanbark oak (Lithocarpus)

Flowers of many grasses, including corn (Zea mays), are wind-pollinated. Staminate flowers (left) and ovulate flowers (right)

Stigma

Stamens

Inflorescences of Elymus (= Agropyron) a grass related to wheat

A grass spikelet, a cluster of florets. Spikelets may be arranged in a variety of inflorescence types (see slide #25)

An individual grass floret dissected out of a spikelet

The grass floret dissected still further, to show the androecium and gynoecium

A typical inflorescence of a composite (Asteraceae)

Ray flowers

Disk flowers

Composite inflorescence and flowers dissected and explained

Not all composites have disk flowers

Thistles have only disk flowers

Positioning of the ovary within a flower, from ancestral (left) to derived (right)

Placentation, the arrangement of ovules within the ovary

Dodder (Cuscuta), a parasitic plant in the Convolulaceae

Rafflesia, the world’s largest flower, is parasitic on roots of Vitaceae

Indian-pipe (Monotropa uniflora) is a parasite on ectomycorrhizal fungi that tap sugars from nearby photosynthetic host plants

Flowers and fruits of Magnolia grandiflora, a woody magnoliid

Flowers of Aristolochia grandiflora, a paleoherb

Rhizanthella, a mycoheterotrophic orchid that grows underground

Flowers of Rhizanthella exposed

The vanilla orchid; hand pollination to insure good yield of pods

Longhorn beetle pollinating a lily; inset, beetle fossil of 95-98 MYA

Beetle pollinators that are pollen-feeding (left, on Hepatica, Ranunculaceae) or nectar-drinking (right, on Angophora, Myrtaceae)

Fly-pollinated flowers are often dark reddish, and stinky, like this South African succulent Stapelia schinzii (Asclepidaceae)

Honey bee pollinating rosemary (Rosemarinus officinalis, Lamiaceae)

A sweat bee pollinating a cactus flower

Foxglove (Digitalis, Scrophulariaceae) has a landing pad and “honey guides” for bee pollinators

Marsh marigold (Caltha palustris, Ranunculaceae): what WE see

Marsh marigold (Caltha palustris, Ranunculaceae): what BEES see

A bumblebee in a California poppy (Eschscholzia californica, Papaveraceae)

The “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

A fly-pollinated orchid (Piperia elegans, Orchidaceae, left), and a mosquito carrying a dumbbell-shaped pollinium on its head (below)

A fly on a camas lily (Zygadenus) with bright yellow nectaries

Many butterflies and moths are pollinators, and drink nectar through their long proboscis (arrow)

A yucca moth on a Yucca flower (Asparagaceae); larval moths eat some of the seeds in the resulting yucca fruit

Bird-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.

A 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.

The nectar of these columbine flowers is only (?) available to birds

Poinsettias (Euphorbia pulcherrima, Euphorbiaceae) are pollinated by birds, but ants like the nectar, too.

A lesser long-nosed bat (Leptonycteris curasoae) getting a faceful of pollen at a cactus flower at night.

Threadlike 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.

Staminate 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.

Pollinators 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.