Plants IIPlants II

The Vascular Plants

Hypericum sp.Photo by Alan Mulvey

THE SEED PLANTS I

Gymnosperms

Evolution of the Seed PlantsEvolution of the Seed Plants

Heterosporous Seed: (embryo & stored food) Evolution of pollen

Megagametophyte develops within ovule* Microgametophyte develops within pollen grain*Pollen grains evolved by reduction of male gametophyte

& protection by pollen wallsBoth the male & female gametophytes were retained

within the sporophytes

Evolution of the seedEvolution of the seed

One cell megaspore is retained within megasporangium It is protected by integument It develops into mature megagametophyte within the embryo sac After fertilization, it matures into the embryo (sporophyte)

Lilium: PollenLilium: Pollen

Generative cell (2 sperms)

Tube cell

Pollen wall

Pine: PollenPine: Pollen

Generative cell

Tube cell

Wings

Evolutionary transition from a Evolutionary transition from a gametophyte to sporophyte dominancegametophyte to sporophyte dominance

From Keeton, 1993

The Gymnosperms: CharacteristicsThe Gymnosperms: Characteristics

(naked seed)*Water is not required for fertilizationMainly pollinated by windReproductive changes increased protection of

gametesHave sunken stoma & thicker cuticles

Seed ConeSeed Cone

Cone Scale

Two Seeds per Scale

Pine: LeafPine: Leaf

Sunken Soma

Epidermis

Hypodermis

Characteristics Cont..Characteristics Cont..

Have secondary growth - all trees or shrubs Mostly evergreen Xylem has tracheids, lacks vessels (except

some Gnetophytes) Phloem has sieve cells, lacks sieve tube

members

ProgymnospermsProgymnosperms

An extinct group that arose in late Paleozoic Intermediate between seedless & seed

plants Progymnosperms were ancestors of seed

plants Evolved bifacial V.C. & wood (page 411)

Seed Plants I - GymnospermsSeed Plants I - Gymnosperms

Conifers – Coniferophyta Cycads – Cycadophyta Maidenhair tree – Ginkgophyta Gnetophytes – Gnetophyta

Conifers: Phylum ConiferophytaConifers: Phylum Coniferophyta

evolved 290 MYO Constitute the largest group of gymnosperms (50 genera,

550 spp.) Include the tallest & largest trees ever (Giant redwood) Conifers (pine, fir, spruce) have great commercial value

in temperate zones Leaves are either

needles, long or short, as in pines, fir, sprucesmall flat, scale-like as in junipers, cypresses

Mostly evergreen, monoecious

White Pine: White Pine: Pinus strobusPinus strobus

White Pine

White Pine : Twig &Needles : Twig &Needles

White PineWhite Pine

Pollen Cones Seed Cone

Longleaf Pine: Longleaf Pine: Pinus palustrisPinus palustris

Loblolly Pine: Loblolly Pine: P. taedaP. taeda

Loblolly Pine: Loblolly Pine: Pollen ConesPollen Cones

Slash Pine: Slash Pine: P. elliottiiP. elliottii

Turpentine Production

Bald Cyprus Knees: Bald Cyprus Knees: Taxodium distichumTaxodium distichum

Knees

Bald CyprusBald Cyprus

Bald CyprusBald Cyprus

Bald Cyprus: Crown & Seed ConesBald Cyprus: Crown & Seed Cones

Coast Red Wood: Coast Red Wood: Sequoia Sequoia sempervirenssempervirens

Fossil

Sequoia: Coast Red Sequoia: Coast Red WoodWood

Giant Red Wood Giant Red Wood SequoiaSequoia

http://www.habitas.org.uk/gardenflora/sequoiadendron.htm

Giant Red WoodGiant Red Wood

Seed Cones Pollen Cones

http://www.conifers.org/cu/se2/

Balsam Fir: Balsam Fir: Abies balsameaAbies balsamea

Balsam FirBalsam Fir

Seed Cone Leaves

Larch: Larch: Larix deciduaLarix decidua

LarchLarch

Developing cones

Common Juniper: Common Juniper: Juniperus communisJuniperus communis

Tree

Leaves

Juniperus virginiana Juniperus virginiana (Eastern Red Cedar)(Eastern Red Cedar)

Cones

Hemlock:Hemlock: Tsuga canadensisTsuga canadensis

Hemlock: Leaf & ConeHemlock: Leaf & Cone

White Spruce: White Spruce: Picea glaucaPicea glauca

Pollen conesYoung seed cones

Pollinated seed cones

White White SpruceSpruce

Pacific yew: Pacific yew: Taxus brevifoliaTaxus brevifolia

http://www.fw.vt.edu/dendro/dendrology/syllabus/tbrevifolia.htm

Maidenhair tree Maidenhair tree Phylum Ginkgophyta:Phylum Ginkgophyta:

One extant species, Ginkgo biloba (notched leaf)* Reproduction is dioecious Ginkgo is resistant to air pollution (city parks) Pickled seeds are eaten in Asia Ginkgo is now cultivated, could be in the wild

(Asia)

Ginkgo Ginkgo bilobabiloba

Leaves are broad with dichotomous venation

The Ginkgo tree has properties which make it resistant to nuclear radiation. This tree survived the Hiroshima bombings.

www.ginkgo.co.nz/images/ large/ginkgotree.jpg

Ginkgo bilobaGinkgo biloba

Male conesMale cones

Sperms are flagellated, Sperms are flagellated, borne in cone-like structureborne in cone-like structure

Ginkgo Brach & FruitGinkgo Brach & Fruit

Ginkgo Seed Cones

The fleshy part which covers the seed is the integument (offensive odor)No cones but ovules are borne in pairs and stalked

Cycads: Phylum CycadophytaCycads: Phylum Cycadophyta

About 250 MYO, common during the Mesozoic (age of cycads & Dinosaurs)*

Constitute 11 genera (140 spp) Tropical or subtropical Zamia, the only cycad in the States, is native to Florida Most cycads are large palm-like plants Highly toxic (produce neurotoxins & carcinogenic compounds) Sperms are motile, but they are pollinated by beetles Dioecious

Cycad:

Encephalartos humlis

Zamia floridanaZamia floridana

http://plantnet.rbgsyd.nsw.gov.au/cgi-bin/cycadpg?taxname=Zamia+pumila

Male/female cones

Zamia: ConesZamia: Cones

Male

Female

Cycad: Cycad: Encephalartos altensteiniiEncephalartos altensteinii

http://www.calflora.net/southafrica/pageseventeen.html

Cycad: Cycad: Encephalartos feroxEncephalartos ferox

Native to Africa

Encephalartos feroxEncephalartos ferox

Gnetophytes: Phylum GnetophytaGnetophytes: Phylum Gnetophyta

Comprise 3 genera (70 spp) The most derived group of gymnosperms Similarities to angiosperms: Produce vessels (in xylem) Their strobili are similar to angiosperms’ inflorescence Double fertilization in Ephedra & Gnetum Produce nectar & insects play a role in pollination Leaves are borne in opposite pairs

The genus The genus GnetumGnetum

Has 30 spp (trees & woody vines)* Native to SE Asia, tropical Africa, Amazon

basin Have broad leathery leaves similar to dicot.

Gnetum gnemonGnetum gnemon

Gnetum: LeafGnetum: Leaf

Gnetum: Gnetum: Pollen ConesPollen Cones

Gnetum: Seed ConesGnetum: Seed Cones

The genusThe genus Ephedra Ephedra

Has 35 spp Tough shrubs inhabit deserts in N Mexico

and SE USA* Leaves reduced and scale-like Dioecious or monoecious

EphedraEphedra

- Cures respiratory problems

- Used in weight loss prog.

- A stimulant

Ephedra: Pollen Cones

Welwitschia mirabilisWelwitschia mirabilis

The most bizarre vascular plant* Native only to deserts of South Africa,

Angola, & Namibia Dioecious

WelwitschiaWelwitschia

- Most of the plant is buried in the sand- Aboveground discoid wide stem (1.5 m wide) produces 2 long

leaves

DISK

Welwitschia HabitatWelwitschia Habitat

http://www.csdl.tamu.edu/FLORA/imaxxwlw.htm

Population

Welwitschia HabitatWelwitschia Habitat

Welwitschia ConesWelwitschia Cones

WelwitschiaWelwitschia

Male cones

Female cones