Transcript

Gnetophyta

Gnetophyta - Taxonomy
• 3 very distinct lineages: • Gnetopsida
– Ephedrales
• Ephedraceae
– Ephedra

– Gnetales
• Gnetaceae
– Gnetum

– Welwitschiales
• Welwitschiaceae
– Welwitschia

in total • Opposite or whorled leaves • Vessels in xylem – Only gymnos.Shared Characters • c.Gnetophyta . 80 spp. with vessels & tracheids • Compound ♂ and ♀ strobili • Further reduction of male and female gametophytes • Sperm not motile .

but 250 MYA for Welwitschiales) .Gnetophyta • Seeds with 2 integument layers – Inner forms micropylar tube that exudes pollen droplet – Outer derived from a fused pair of bracts (not true integument) • Short fossil record (< 65 MYA for Ephedrales and Gnetales.

somewhat flowerlike structures. Winteraceae) • Recent data suggest a relationship to Pinaceae .g..Gnetophyta – Evolution • Share features with gymnosperms AND angiosperms – Gymno: seeds not enclosed in ovary – Angio: vessels in wood. double fertilization • BUT some primitive angiosperms do not have vessels (e.

& S. America & Eurasia • 6 species native in SW USA – “Joint Fir”. “Mormon Tea” – Soothing properties used by Mormon pioneers .Ephedrales • ~ 40–50 species • Native to arid/Mediterranean regions of N.

Ephedra • Ephedra sinica (from Asia) – Original source of Ephedrine and Pseudo-ephedrine • Both compounds increase heart-rate. metabolism – Diet aids (dangerous – Methamphetamines (Ephedrine) – Decongestant (Pseudo-ephedrine) .

Ephedra: Vegetative Morphology • Branching shrubs • Whorled. scale-like leaves • Jointed stems • (Superficially similar to Equisetum) .

Ephedra: Reproductive Morphology • Usually dioecious – Some species monoecious • Female and male strobili – Complex and compound – Similar sized – Scattered along stems .

Ephedra: Megastrobilus • Compound – Ovules borne on lateral branches – Pair of bracteoles = “outer” integument .

Megastrobilus Bracts Inner integument Nucellus Tetrad of spores Ovules Bracteoles Megastrobilus .

Megagametophyte integument outer envelope nucellus archegonia megagametophyte .

Ephedra: Seed “Inner” integument remnants Seed Bracts .

Microstrobilus .

SE Asia • Mostly woody vines – Lianas (rare among gymnosperms) • Leaves opposite. with net venation (similar to many angiosperms) .Gnetum • 30 species • Humid tropics – S. Africa. America. broad.

Gnetum – reproductive morphology • “Functionally dioecious” – Megastrobilus with abortive microsporangia – Microstrobilus with abortive megasporangia • No real archegonium – Any cell (or 2 cells) can function as egg .

Gnetum female male .

mirabilis – (Latin: mirabilis = wonderful) • One of the weirdest plants on the planet! • Coastal deserts of SW Africa (Namibia) – <1” rainfall per year.000 years • Most of plant is underground .Welwitschia • Monotypic – W. so plants get water from ocean fog that rolls in every night • Can live > 2.

Welwitschia • Only 2 permanent leaves for the entire plant. for its entire lifespan! – Grow continually from basal meristems – Leaves shredded over time by wind • Huge taproot (up to 30-40’ deep) – Plus “surface” roots that suck up the moisture from the nightly fog • Dioecious .

Young Plant •Leaves still somewhat intact 1st leaf 2nd leaf .

Older plant •Still only 2 leaves! .

Welwitschia •2 “scaly bodies” sometimes interpreted as leaves •Scars are from old strobili Strobili Basal meristem Scaly bodies (2) Leaf .

Microstrobili Microstrobili Stamen-like appearance .

Megastrobili • Fertilization bizarre – Megagametophyte highly reduced (no archegonia) – Also produces a tube with grows to meet the pollen tube – Zygote then travels back into megagametophyte .

Megastrobili Megastrobilus Pollen droplet Seed .

. 2002) suggest that extant ones do (based on 8 genes from 3 genomes) – Likely paraphyletic if extinct lineages included • Gnetophyta probably NOT sister to angiosperms – Morphological characters convergent .Recap • Do gymnosperms for a monophyletic group? – A definite maybe – Recent data (Soltis et al.

Recent Phylogeny Gnetum Welwitschia Ephedra Pseudotsuga Taxus Cryptomeria Podocarpus Araucaria Gnetophyta Pinaceae Pinophyta Ginkgophyta Cycadophyta Angiosperms Outgroups .