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• Plant form, function, and diversity are key topics.
• The learning objectives include describing the evolutionary history of land plants, identifying differences between monocots and dicots, describing economically important plant species, and explaining the success of specific plant groups.
• Angiosperms co-evolve with insects

Phylogeny of Land Plants

• Land plants evolved from green algae.
• Alternation of generations and protected embryos are characteristic of land plants
• Vascular plants have vessels for bulk flow, specifically xylem and phloem.
• Seed plants have seeds and pollen.
• Seed plants are independent of water for fertilization.

Diversity of Land Plants

• The most diverse group of plants is angiosperms.
• Bryophytes are mostly mosses and disperse by spores (no seeds).
• Gymnosperms means "naked seed".

Plant Phylogeny

• Angiosperms didn't evolve until the Mesozoic era.
• Grasses are the most important food source for humans.
• It is useful to know when each group of plants appears in the fossil record.

Plant Reproduction

• Plant reproduction involves an alternation of haploid and diploid generations.
• Plants have a haploid generation that produces gametes by mitosis.
• "Gen 1" refers to the haploid generation while "Gen 2" is the diploid generation.
• Unlike animals, plants have two multicellular generations.

Bryophytes

• Bryophytes are typically small plants.
• Bryophytes absorb nutrition through their body, not roots, and are found in moist environments.
• Bryophytes do not produce roots.
• Bryophytes are haploid dominant.
• Bryophytes reproduce by unicellular spores rather than seeds.

Bryophyte Specialization

• Peat bogs store carbon and keep it from returning to the atmosphere.
• Sphagnum moss has specialized cells that hold onto water like a sponge.
• Sphagnum moss secretes protons that acidify the surrounding water and phenols that slow decomposition.

Vascular Plants

• Peat bogs are non-vascular plants
• Vascular plants have xylem and phloem.
• Vascular plants first appeared in the fossil record 425 million years ago.
• The evolution of xylem and phloem provided vascular plants with advantages in size and hydration

Fossil Lycophytes

• Fossil lycophytes had roots and leaves and well-defined tissue layers.
• Lycophytes had meristematic tissue that gives rise to all tissues of the plant body.
• Modern lycophytes are smaller than their fossil ancestors.

Lycophyte Diversity

• The leaves and roots of lycophytes evolved independently from those of other vascular plants.
• Lycophyte leaves have only a single vein
• Coal swamp forests, dominated by tree-sized lycophytes, formed widely about 320 million years ago.
• These forests are called coal swamp forests because when they got buried, they became coal

Ferns and Horsetails

• Some ferns have stems visible above ground, but not all.
• Ferns have distinctive leaves that uncoil during development from tightly wound "fiddleheads".
• Many ferns appear to only be made up of leaves because their stems remain underground
• The horsetails, represented by just 15 living species, produce tiny leaves arranged in whorls, giving them a jointed appearance.
• Horsetail stems are hollow and accumulate high levels of silica.
• Epiphytes live on other plants or outside.
• Azolla, an aquatic fern, has been used as a biofertilizer for rice paddies.
• This fern suppresses weed growth and provides nitrogen to rice paddies.

Seed Plants

• Angiosperms are flowering plants.
• Grasses are a major group of angiosperms.
• Conifers are the most abundant.
• Seed plants do not require external water for reproduction.
• Seeds enhance dispersal, and the nutrient-rich tissue increases the likelihood that the plant embryo will grow

Gymnosperms

• Cycad fossils date back to 280 million years ago and were a dominant plant type in the Jurassic period, but today only about 300 species remain.
• Ginkgos date back to ~280 million years and are now represented by only one surviving species (Ginkgo biloba) over the past 100 million years.
• Conifers include pines, junipers, and redwoods, conifers are mostly evergreen
• Conifers are one of the most economically important groups of plants, and are major sources of timber and paper pulp
• Conifers dominate vast boreal forests, tend become more abundant with elevation, and are common in dry areas

Angiosperms

• Insect pollinators and flowers co-evolved over the past 150 million years
• Angiosperms are plants that have flowers.
• Plants that attract different pollinators diverge to form new species faster than wind-pollinated species.
• Flowering plants with animal pollinators can reproduce even when individuals are far apart, allowing rare species to persist and reproduce

Eudicots & Monocots

• Eudicots first appeared 125 million years ago, and by 80-90 million years ago, most angiosperms were in this group.
• Eudicots have two embryonic cotyledons.
• Monocots have a single cotyledon and make up ~25% of all angiosperms.
• Eudicots have flower parts multiples of 4 or 5, net veined leaves and a taproot derived from a radicle
• Monocots are missing a vascular cambium, so the vascular bundles are scattered though the cross section of the stem.
• Leaves exhibit a parallel arangement of the veins
• Major leaf veins in monocots are parallel, stem vascular bundles are scattered, and roots are adventitious
• Monocots comprise 25% of angiosperms yet make up 70% of food consumed

Eudicots, Notable Species

• Eudicot stem vascular bundles are arranged in a ring with vascular cambium, allowing growth in girth and new vascular tissue to be generated.
• Eudicot leaves are net-veined, radicle is a root
• This group includes potatoes soybeans, cassava, cotton, eggplants, mangos, olives, apples, cucumbers, grapes, oranges, lettuce, spinach

Monocots, Economically Important Species include

• Include coconuts, dates, bananas, onions, palm oil, sugarcane, maize, rice, wheat, and barley.
• Wheat, rice, and maize account for 2/3 of all calories consumed by people.
• The expansion of grasslands through time is notable