BIOLOGY 3404F
EVOLUTION OF PLANTS
Fall 2008
Lecture 17
Thursday November 20, 2008
Chapters 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 windpollinated. 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
Ray
flowers
Disk
flowers
A typical inflorescence of a composite (Asteraceae)
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 pollensac, or pollinium,
which they carry to
the next flower
A fly-pollinated orchid (Piperia
elegans, Orchidaceae, left), and a
mosquito carrying a dumbbellshaped 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.