Angiosperm Phylogeny and Characteristics

• Angiosperms are flowering plants.

Angiosperm Phylogeny

• Angiosperms are spermatophytes (seed plants) that also include gymnosperms.
• Gymnosperm groups include Conifers, Gnetales, Ginkgo, and Cycads.
• Eustele and vascular cambium are traits of seed plants.
• Leaves evolved to be simple.
• Siphonogamy is the development of non-motile sperm.
• Pollen striate and vessels with perforated walls also appeared.

Key Angiosperm Facts

• The largest group of land plants are Angiosperms.
• The most economically important plants are Angiosperms.

Angiosperm Defining Characteristics (Apomorphies)

• Flowers
• Carpels
• Fruits
• Double fertilization with triploid endosperm
• Specialized conductive cells

Flowers

• Flowers are shoot systems bearing modified leaves.
• Perianth is the term for the calyx and the corolla.
• Calyx (sepals) are green and protective.
• Corolla (petals) are colored and attractant.
• Stamens are the male parts.
• Carpels are the female parts.
• The pistil consists of the stigma, style and ovary
• Flower pollination is the transfer of pollen to the ovule.
• Angiosperms use animal pollination.
• It is ancestral for angiosperms.
• It is a more efficient means of pollen transportation.
• Gymnosperms are wind pollinated.
• Some angiosperms are secondarily wind pollinated.
• Animal pollination strategy:
• Attractant: Large or brightly colored perianth with a sweet or rotten odor.
• Reward: Nectar or pollen is offered, and rarely waxes or oils.
• Pollination mechanisms include insects, birds, bats, water, and wind.
• Insect pollinators include bees, butterflies/moths, and flies.

Carpels

• The female reproductive parts of angiosperms
• Carpel is a conduplicate megasporophyll.
• Conduplicate means folded.
• Megasporophyll is the "female leaf, bearing seeds".
• Carpel encloses ovules and seeds.
• Carpels can fuse together.
• Gynoecium refers to all female parts.
• Pistil consists of the ovary, style, and stigma.
• A pistil can be one carpel or many.
• Carpel function:
• Protects young seeds
• Site of pollen germination and can induce self-incompatibility reactions
• Develops into Fruits

Fruits

• Fruit is a mature ovary plus accessory parts.
• Fruit function is seed dispersal.
• There are fleshy and dry fruit types
• Fleshy fruits are dispersed by animals.
• Dry fruits are dispersed mechanically, by wind or water.

Double Fertilization

• Key process in angiosperm reproduction
• Pollen produces 2 sperm cells.
• If a pollen grain germinates, a pollen tube grows down the style toward the ovary.
• The pollen tube discharges two sperm into the female gametophyte (embryo sac) within an ovule.
• One sperm fertilizes the egg to form the zygote.
• The other sperm combines with the two polar nuclei to form a triploid cell, which develops into the nutritive tissue called endosperm.
• Therefore:
• Sperm (n) + egg (n) --> Zygote (2n)
• Sperm (n) + 2 polar nuclei (n) --> Endosperm (3n)
• Triploid endosperm is nutritive tissue in angiosperm seeds.
• The extra set of genes may help with rapid development and increased genetic variation.
• Fertilization occurs soon after pollination in angiosperms.
• Seeds are produced rapidly for angiosperms.
• This rapid turn around creates selective advantages, specifically for annual herbs.
• Gymnosperms have a long period between pollination and fertilization.
• Seeds of gymnosperms mature slowly, in 1-2 years.

Specialized Conductive Cells

• Most angiosperms have vessels and perforation plates.
• Angiosperms have sieve tube members with sieve plates which are bigger pores in end walls.
• Vessels and sieve tube members are more efficient in water and sugar conduction

Angiosperm Classification

• Old classification:
• Dicots have two cotyledons (seed leaves)
• Monocots have one cotyledon.
• In modern phylogeny, monocots are monophyletic.
• Apomorphies of monocots include 1 cotyledon, atactostelic vasculature, absence of vascular cambium and parallel leaf venation .
• Monocots include palms, orchids, irises, and grasses.
• Traditional "dicots" are paraphyletic.
• Eudicots are pollen tricolpate and monophyletic.
• Eudicots include most angiosperms like roses, legumes, daisies, and oaks.
• All other Angiosperms have pollen with one aperture, whereas eudicots have pollen with three apertures.