Last day… got started on Kingdom Plantae, general characteristics, & looked at ‘non-vascular’ groups (Hepatophyta, Anthocerophyta, & Bryophyta)

Then, started looking at characteristics of the vascular plants

Vascular plants evolved specialized roots to absorb water & minerals from the soil

- and specialized leaves, microphylls (small, single vein) in lycophytes & megaphylls (large, branched veins) in most vascular plants

Another innovation was sporophylls, modified leaves bearing sporangia

Some seedless vascular plants (and all seed plants) became heterosporous: megaspores for female gametophytes, males from microspores

Seedless vascular plants placed in 2 phyla:Phylum Lycophyta – Club mosses, spike mosses, quillworts – 1200 spp.- club mosses & spike mosses produce clusters of sporophylls called strobili- some are epiphytes (on other plants), quillworts are aquatic

Phylum Pterophyta – ferns, horsetails & whisk ferns - 12,000 species (15 horsetails, 7 ‘whisk ferns’)

Ferns widespread, but primarily in moist areas, may reach tree size- horsetails may be abundant in temperate areas, hollow stems with silica (‘scouring rush’)- whisk ferns may be ferns that lost leaves, roots?

Success of seedless vascular plants may have caused an ice age… and global warming

Ferns & other seedless vascular plants not of huge economic importance but…

Only 2 main groups of plants left : Gymnosperms & Angiosperms…

But, those 2 groups contain most living plants, the Gymnosperms & Angiosperms - seed plants seem to be monophyletic

Success of seed plants related to advantages of producing seeds: fertilized embryo & its food supply, surrounded by a protective coat

Along with seeds, 4 associated evolutionary changes:

1) reduction of gametophyte stage

2) consistently heterosporous: microspores male gametophytes, megaspores female gametophytes

- separate gametophytes will live different lives

3) Ovules & production of eggs: sporophyte produces protective layer of tissue (integument) enclosing megasporangum & its megaspore

Ovule = integument + megasporangium + megaspore

Megaspore germinates within ovule, develops into tiny

female gametophyte - produces egg which will eventually be fertilized

Seed contains tissue from three generations of plants: 1) seed coat from mature sporophyte 2) food supply from female gametophyte 3) embryo is new sporophyte generation

Seed is protected, capable of dispersal, can remain dormant for very long periods, & has food supply to begin growth

4) Pollen grains: male gametophyte surrounded by pollen wall (partly secreted by sporophyte)- a separate, multicellular generation, even if reduced to an extreme (2 cells, or 3 after germination)

Pollen grain capable of long dispersal, tough & resistant, & sperm nuclei do not require external H2O for fertilization

Seed Plants divided into 2 main groups:Gymnosperms (‘naked seeds’) & Angiosperms (‘container seeds’)

Some ancestors of seed plants found in fossil record ~ 380 MYA, & ‘seed ferns’ by 360 MYA

Carboniferous forests dominated by lycophytes, horsetails & ferns but early gymnosperms by 305 MYA

Drier conditions of Permian period favored gymnosperms over seedless vascular plants, & dominated through whole Mesozoic era

Living gymnosperms in 4 phyla, some not very diverse…

Phylum Cycadophyta – Cycads (Sago palms)- only about 130 spp. now but abundant in Mesozoic

Male and female cones on separate plants

Phylum Ginkgophyta – Ginkgos- well known as fossils (80 MYA), but only one surviving sp.- fan-like leaves, fruit with interesting odor

- turns yellow, & drops leaves abruptly

Phylum Gnetophyta – Gnetophytes- only 3 genera…

Welwitschia – one sp. in SW Africa

Ephedra – one genus w. about 40 spp. in arid areas

…and Gnetum, one genus of trees, vines or shrubs, about35 spp. in warm areas of Old World

Final phylum of gymnosperms: Phylum Coniferophyta - the conifers (including pines, spruces, cedars…) with

about 600 spp. (largest group of gymnosperms)

- often large & long-lived, dominate large areas of northern forest, & grow elsewhere in rocky or sandy soils

Next big group: Phylum Anthophyta - Angiosperms or ‘flowering plants’

- extremely diverse group with about 170,000 spp.

Flowering plants are diploid sporophytes, produce microspores and/or megaspores

- asexual reproduction, no gametes or fertilization…

- microspores develop into male gametophytes (inside pollen grain),

- megaspores develop into female gametophyte = embryo sac

Pollen transferred to stigma, normally cross-pollination

Female gametophyte now has 8 nuclei (7 cells)

- 2 sperm cells carry out double fertilization: one fertilizes egg, other fuses w. 2 nuclei in central cell

- central cell becomes triploid endosperm (food supply for seed)

Embryo, w. endosperm & integuments, develops into seed

- surrounding ovary tissue forms fruit

Angiosperms probably split from gymnosperms about 305 MYA, but subsequent history not well known- living lineages shared a common ancestor ~150 MYA

Earliest branch in phylogeny is Amborella, shrub found only on New Caledonia- lacks vessels in xylem

Other early branches include water lilies & the star anise & relatives- star anise family has female gametophyte w. only 4 nuclei, some spp. used as spices and medicines

Magnoliids are more speciose (~8,000 spp.), including magnolias, laurels, & black pepper plant

The 2 big groups of angiosperms are the Monocots (~70,000 spp.) & the Eudicots ( ~ 170,000? spp.)

Monocots include orchids, palms, lilies, grasses…

Eudicots include… lots! (oaks, peas, roses, potatoes, etc.)

A number of distinctive characteristics generally make Monocots & Eudicots fairly easy to distinguish

The value of seed plants to humans is… priceless

- six species (maize, rice, wheat, potatoes, cassava & sweet potatoes) provide 80% of calories consumed

- source of building material, fuel, pulp, etc.

- coffee, tea, spices & sugar also impt.

Many drugs from seed plants, currently or originally discovered in plants- most plants not investigated yet for potential uses

No less important to organisms around the world, at least in terrestrial habitats