The Great War Project The Biology of the Flower It’s All About Sex!

Perfect Flowers Have both male and female parts Note: ‘carpel’ in diagram may also be called the pistil

Monocot vs. Dicot Flowering plants (Angiosperms) fall into two broad plant groups; the monocots and the dicots Distinguishing the two groups is quite easy Look at leaf veins; if veins are branching with a netted pattern the plant is a dicot; if leaf veins are parallel, then the plant is a monocot Seeds of dicots can be split (eg. beans) while seeds of monocots cannot be split (eg. corn)

Flower Differences Monocots have flower parts in multiples of 3 while dicots have flower parts in multiples of 4 or 5 (note: petals may be fused in some flowers) Many monocots have sepals that look like petals giving the flowers the appearance that they have 6 petals. When petals and sepals look the same, they are called tepals.

Dicot flowers

Monocot flowers

Imperfect Flowers: Monecious vs. Dioecious While most flowers are both male and female, some plants have separate male and female flowers Mono = one ( monoecious plants have separate male and female flowers on the same plant) Dio = two (dioecious plants have separate male and female flowers on separate plants)

Monoecious

Dioecious

Flower colour important Certain colours attract certain pollinators Moth pollinated flowers are generally white or highly fragrant, esp. at night Bee flowers often pink, purple and blue Butterfly flowers often yellow, orange, red Bird-pollinated flowers often red, tubular with no fragrance

Human vs. Insect Vision

Flower Shape Flowers fall into two broad shape categories Radial Symmetry (Actinomorphic) Bilateral Symmetry (Zygomorphic)

A Special Case: Daisies A ‘single’ daisy is actually a tight cluster of numerous, tiny, individual flowers Collectively, they are referred to as a ‘head’ of flowers Outer flowers have a single, large modified petal (called ray flower) Inner flowers are called disc flowers

What is the purpose of this variability in flowers? Ultimately, results in pollination Mode of Pollination – Animal vs. Wind Many monoecious and dioecious plants are wind pollinated Actinomorphic (radial symmetry) flowers most popular with flies/butterflies Zygomorphic (bilateral symmetry) flowers most popular with bees, hummingbirds

Outbreeders vs. Inbreeders Can often tell by looking at the flower whether it is an inbreeder (self-pollinating) or outbreeder (cross-pollinator) Inbreeder characteristics Few flowers Small flowers No fragrance Mono-coloured No stripes (nectar-guides) on flowers Anthers close to stigma Stigma not obviously visible

Outbreeders vs. Inbreeders Outbreeder characteristics Large number of flowers Large flowers Fragrant Brightly coloured Stripes (nectar-guides) present Anthers spaced from stigma Stigma large and obvious

Advantages of cross-pollination Increases genetic variability Adaptation to changing conditions Strong evolutionary potential Successful colonization long-term BUT: depends on effective mode of cross-pollination

Self-pollination Advantage: reliable seed set regardless to pollinator activity and can allow a successful individual to rapidly colonize an area in the short-term Disadvantage: less genetic variability thus cannot adapt to changing environment Evolutionary dead-end

Orchids : the Ultimate Flowering Plant Largest group of flowering plants – 20,000 species Considered the most highly-evolved flower Little wastage of pollen Often use a specific group of pollinators, even a specific species of pollinator Orchid use mimicry more than any other group of flowers PROBLEM: VERY sensitive to environmental change and at risk for extinction

1/3 of orchids use mimicry Utilize pseudo-copulation May produce fragrance that mimics the pheromones of a female insect Part or all of the flower appears like the female insect Males try to mate with the flower, bringing about pollination

MUN Botanical Garden For more information, please contact: Todd Boland, Research Horticulturist MUN Botanical Garden Memorial University of Newfoundland St. John’s, NL, A1C 5S7 Email: bgprograms@mun.ca