Botany 124

FLOWER STRUCTURE & FUNCTION

I. Phylum: Anthophyta, Angiosperms, 250,000 spp.
a. Unique features
1. Flowers
2. Fruits
3. Double fertilization forms a zygote and primary endosperm nucleus becomes triploid embryo-nourishing endosperm
b. Class-Monocotyledons: grasses, lilies, irises, orchids, palms (70,000)
c. Class-Eudicotylendons: (172,500 spp.) trees, shrubs
d. Class-Magnoliids: (6,250 spp)
· Oil cells (nutmeg, laurel, papper)
· Large robust flowers with many free parts arranged in spiral
· 20 families, including Magnoliaceae, Lauraceae, Calycanthaceae (spicebush family)
(e. Basal Angiosperms: 1,250)

II. Flower Structure
a. Determinate shoot with sporophylls
b. Solitary, Inflorescence, Peduncle, pedicel, receptacle
c. Structures
· Sterile modified leaves: sepals and petals
· Fertile modified leaves (sporophylls): stamens and carpels
· Androecium: stamens collectively, filament & anther
· Gynoecium: carpels. Pistil. Simple or compound
· Ovule(s) within carpel connected by funiculus
1. Megagametophyte or embryo sac - 8 nuclei, 7 cells
2. 2 Polar nuclei in center
3. 2 Synergids on each side of egg
4. egg
5. 3 Antipodal cells
III. The Flower: A Functional Unit
a. Pollination: Release, transfer and deposit of the microgametophyte (pollen) on the receptive portion of the carpel (usually stigma).
· Necessary prerequisite to fertilization
· Need of a vector
· Pollination efficiency
b. Breeding systems
· Autogamy- pollination within 1 flower
· Allogamy- pollination between 2 flowers
1. Geitonogamy - 2 flowers, 1 plant
2. Xenogamy - 2 flowers, 2 plants
· Apomixis- reproduction without fertilization by development of unfertilized egg
· Genetic self-incompatibility
c. Flower variations that promote outcrossing
· Perfect- imperfect, staminate/carpellate
· Monoecious/dioecious
· Dichogamy: promotes outcrossing
1. Protandrous
2. Protogynous
3. Heterostyly
d. Vector Attractants
· Primary Attractants-food (pollen, nectar, flower parts), brood place, heat
· Secondary Attractants
1. flower color, odor, shape
2. inflorescence
IV. Pollination precedes Fertilization
a. Abiotic vectors
· Anemophily- Wind
· Hydrophily- Water
b. Biotic Vectors
· Birds, bats, insects (bees, wasps, butterflies, moths, flies, beetles, ants)
c. "Promiscuous Flowers"-High energy cost
· Magnolias and many cacti
· Beetles
d. Varying degrees of "selective flowers"
· Saguaro
· Yucca whiplei and the female pronuba moth
e. Deception
· Calochilus campestris-- pseudoparasitism
· Oncidium - pseudoaggression
· Ophrys and Trichoceros - pseudocopulation
· Coryanthes -- Traps