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Gymnosperms Pages 389-402; Flora of east Texas Vol I Ponderosa pines: Big Bend National Park, Texas Gymnosperms are Seed Plants ● ● ● ● “Gymnosperm” = “Naked Seeds”. 4 of 5 branches of a monophyletic clade called Seed plants. Seeds (ovules) not enclosed in a fruit (carpel), but exposed at pollination time. ● Seeds may later be enclosed by fused cone scales– juniper “berries”, etc. Always woody (some angiosperms may be herbaceous). What are Seed Plants? 1) Heterosporous Life Cycle--2 kinds of spores: ● Megaspores → egg-producing gametophyte (megagametophyte). Develops inside ovule. Microspores → sperm-producing gametophyte (microgametophyte). – ● Ovulate (seed) cones 2) Microgametophyte (=pollen) is mobile (wind). 3) Presence of ovules: Pollen (male) cones The Ovule: a Special Sporangium Megasporangium (nucellus) + integuments. ● Megaspores not released: Remain in ovule where spore germinates & female gametophyte forms & produces egg. Fertilization of the egg is & embryo development occurs within the ovule. – ● ● Mature ovule with embryo = Seed. Gametophyte ovule Gymnosperm (Pine) Life Cycle: Sporophyte (2N) Seed w/ embryo Ovulate (female) cone Male cone Mitosis Zygote Fertilization Pollination Pollen tube w/ sperm 2N 1N Pollen Gametophyte (1N) Meiosis MicroSpores Megaspore in ovule Mitosis Archegonium & egg (flowering plants) Magnoliophyta Cycadophyta Gnetophyta Ginkophyta Gnetophyta Pinophyta Phylogeny of Seed Plants: Magnoliophyta Cycadophyta Ginkophyta Pinophyta Classification of Gymnosperms: ● ● ● ● Four existing lineages: Gnetophytes, Cycads, Gingkos, & Conifers. Together, only 840 species, 86 genera, 17 families (p. 389). But, many familiar & important species (pines, etc). Division Gnetophyta (P. 389). ● ● Monophyletic despite variable appearance of members. Share several unusual features: ● multiple axillary buds, compound pollen strobilli (cones), unusual pollen morphology. Gnetum Welwitschia Ephedra Gnetophyta, Ephedra, (Ephedraceae) ● ● ● ● p. 389-390 40 species of desert, semi-desert shrubs, vines. Jointed stems & branches & small scale-like leaves. 1 species native to SW margin of E. Texas, none in Pineywoods, 6 in TX. (p. 390). Alkaloid ephedrine. Ephedra antisyphilitica Palo Duro canyon St. Park, TX Ephedra aspera Big Bend National Park, TX Gnetophyta,Welwitschia, (Welwitschiaceae) ● 2 ragged, continuously growing strap-like leaves ● Cones (strobili) on rim. ● Native to desert in Namib Desert, S.W. Africa. Gnetophyta, Gnetum, (Gnetaceae) ● ● ● ● Broad-leaved tropical forest vines & trees. Roughly 40 species. Superficially resemble flowering plants. No Texas natives. Gnetum Cycadophyta: (Cycads) p. 400-402 ● ● ● ● ● ● Palm like / fern like plants, unbranched. Short woody trunk, pinnately compound leaves. Large, simple strobili. Dioceous. Insect pollination. Roughly 145 sp.; mostly tropical & Southern Hemisphere. Nitrogen-fixing bacteria in coralloid roots. No Texas natives, but grown here as ornamentals. Ginkophyta: (p. 402-403) ● ● ● ● ● Ancient lineage originating in Permian, widespread in Jurrasic, now mostly extinct. Free branching Trees, branches with spur shoots & long shoots. Fan-shaped leaves with dichotomous venation. Trees dioecious: ● Stalked ovules with fleshy outer layer. ● Microsporangia in catkin-like structures, pollen releases motile sperm. Only Ginkgo biloba exists today: ● Fossils resembling it worldwide in distribution. ● Now restricted in wild to remote area in S. China. ● Popular landscape tree in U.S. & Europe (including Texas). Gingko leaves Gingko biloba Pinophyta (Conifers) p. 391-400 ● ● ● ● ● Trees, shrubs with needle-like, linear, or scale-like leaves. Conelike ovule-bearing structures (Strobili). ● Compound (several branching) megastrobilus. ● Simple unbranched microstrobilus. 8 families, 68 genera, 629 species, (2 Texas families). Fossils from late Carboniferous (360-286 MYBP). 5 native Pineywoods species. Conifer: Larix cajanderi, Kamchatka, Russia Pinophyta: Pincaceae (Pine Family) ● Vegetative Features ● ● ● Scale Trees, shrubs. Needle or linear leaves in bundles (fascicles) on short spur shoots (Pinus) or alternate along stems. Reproductive Features ● ● ● Ovulate Cones (megastrobili) – Scales spiral around woody axis. – 2 ovules on upper surface of scale. – Bract subtends each scale; bract not adnate to scale. – Cones longer than broad. – Seeds winged. Bract Plants Monecious: Pollen cones (microsrtobili) – 2-6 microsporangia under scales. Pollen cones Pinophyta: Pincaceae (Pine Family) ● Other Features: ● 10 genera, 200 species. Widespread especially northtemperate, boreal & subtropics ● Economically, ecologically most important gymnosperm family. Scale Bract Pollen cones Major Pinaceae Genera: ● ● ● ● Pinus: Common in mountains, northern, southern US, Mexico. ● 3 Texas Pineywoods species. Picea (spruce) dominant in boreal and mountain forests Abies (fir) dominant in boreal and mountain forests. Pseudotsuga (douglas fir) -major western lumber tree. Picea mariana forest in Sascatchewan Abies Picea Pseudotsuga Menziesii (douglas fir) An important western USA tree. Native Pinaceae: longleaf pine (Pinus palustris) Native Pinaceae: loblolly pine (Pinus taeda) Native Pinaceae: shortleaf pine (pinus echinata) Cupressaceae (Cypress or Redwood Family) ● ● ● Vegetative Features: ● Trees, shrubs, often large, long-lived. ● Scale like or small needle leaves, alternate or opposite. Reproductive Features: ● Ovulate cones small, round (globular). ● Cone scales adnate to subtending bracts. ● Dry & woody or fleshy (juniper “berries” at maturity. ● Plants monoecious or dioecious. Other Features: ● Roughly 110-130 species. ● Includes redwoods, sequoias, baldypress & junipers. Juniperus Taxodium Important Cupresaceae Genera: ● ● ● ● ● Juniperus (juniper). ● J. virginiana native to east Texas. Thuja (White cedar), ● Northern/ Great Lakes swamps & lowlands. Sequoiadendron gigantea: (giant sequoia) California mountains. Sequoia sempervirens: redwood ● Coastal mountains, California. Taxodium: (baldcypress) ● Swamps in southeastern USA. Sequioiadendron Native Cupressaceae: baldcypress (Taxodiuim distichium) Native Cupressaceae: Juniperous virginiana (eastern red cedar) Cupressaceae: Coastal Redwood (California) Sequoia sempervirens: Other Conifer Families: Taxaceae Taxus (yew) Taxus baccata Other Conifer Families: Araucariaceae Araucaria angustifolia: (southern Brazil) Other Conifer Families: Podocarpaceae Podocarpus totara New Zealand Podocarpus sellowii Brazil The End Version 13.01