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Plant Diversity and Evolution Part 3 Gymnosperms Poland’s pine crooked forest (man made) Outline • Introduction • Phylum Pinophyta – The Conifers • Other Gymnosperms • • Phylum Ginkgophyta – Ginkgo • Phylum Cycadophyta – The Cycads • Phylum Gnetophyta – The Gnetophytes Human Relevance of Gymnosperms • Conifers • Other Gymnosperms Introduction • Gymnosperms are vascular plants that produce seeds. • These are the oldest known seeds (late Devonian, more than 350 million years ago) but it is widely accepted that Gymnosperms evolved in the Carboniferous period. • The first seed plants were fernlike in appearance and for a long time were classified as pteridosperms (seed ferns) today, these have been reclassified as gymnosperms (in the cycads group) Adaptations that appear in Gymnosperms • Plants can live without being so dependent on water. • Instead of spores, plants developed pollen (so fertilization can occur without water) • Seeds: The production of a seed protected by a seed coat lets the embryo be transported and developed elsewhere. The evolution of the seed • Seeds provide a significant adaptation for plants on land. • Protective seed coat • Supply of food for embryo • Capable of dormancy in unfavorable environmental conditions Gymnosperms Characteristics • Xylem has only tracheids (except the Gnetophyta). Soft woods. • Deep root systems • Leaves like needles, scales or flat thin surfaces (a few exceptions) • There are seed bearing plants, but they do not have flowers, they have reproductive structures known as strobilus/strobili or cones. They can be dry or fleshy. Gymnosperm Angiosperm Characteristics, continued • Wind pollinated. • Wind dispersed seeds • In angiosperms, the seeds are produced after fertilization inside an enclosed ovary. In gymnosperms, the ovule is exposed. The term gymnosperm means “naked seed” The Female Cone • Inside the female cone, we find ovules. These ovules are exposed. • Inside the ovules, we find the female gametophyte or nucellus (in angiosperms, this was known as the embryo sac). • Inside the nucellus, we find the egg cell (megaspore). The Male Cone • Pollen cones produce pollen grains Gymnosperm vs. Angiosperm • In angiosperms, the seeds are produced after fertilization inside an enclosed ovary (see apple). • In gymnosperms, the ovule is exposed, thus the seed is also exposed (Gymnosperm refers to the exposed nature of the seeds. • Gymnosperms classification Four living phyla • Pinophyta: It bears distinct strobili (cones), needlelike leaves arranged in clusters. There are about 600 species of pines, firs, spruces, cedars, araucaria (monkey tree), etc… • Ginkgophyta: Real leaves, notched, broad, fanshaped leaves with evenly forked veins. Plum like seeds enclosed in fleshy covering. One single living species, Ginkgo biloba • Cycadophyta: Cross between tree fern and palm. The strobili (cone) is in the center. There are about 300 species • Gnetophyta: Vessels and tracheids in xylem. About 70 species Phylum Pinophyta. The Conifers • The conifers, division Pinophyta, also known as division Coniferophyta or Coniferae. • The total number of species is relatively small (a total of 65– 70 genera and 600–630 species), conifers are of immense ecological importance: They are the dominant plants over huge areas of land, especially the boreal forests of the northern hemisphere, and in similar cool climates in mountains ecosystems. • The Podocarpaceae (a family of conifers) are a large family of mainly Southern Hemisphere conifers. The family is a classic member of the Antarctic flora ( Australasia, particularly New Caledonia, Tasmania, and New Zealand, and South America (primarily in the Andes mountains). Phylum Pinophyta. The Conifers • Species of Phynophyta includes cedars, Douglas-firs, cypresses, firs, junipers, kauri, larches, pines, hemlocks, redwoods, spruces, and yews. • Pines (Pinus) is the largest genus and the dominant trees in coniferous forests of Northern Hemisphere. • Include world’s oldest known living organisms: Bristlecone pines. Pinus longaeva, White Mountains, eastern California. 5065 years old. Tom Harlan research. Who is older? • Extra Credit. Who is older Pando or species of Pinus longaeva? • Who/What is Pando? Explain the nature of Pando and why would you consider Pando or Pinus longaeva older? • Explain botanically the details and discuss with wellsupported arguments what is your opinion in favor of one or the other. Phylum Pinophyta. The Conifers Leaves needlelike and arranged in clusters (fascicles) of two to five needles. The needles have modifications that enable them to survive harsh conditions. These includes: • Hypodermis located below the epidermis. One to two layers of thickwalled cells. • Thick cuticle • Recessed or sunken stomata • Resin canals. Resin is antiseptic and aromatic, prevents development of fungi, and deters insects. Pines Reproduction • Seed cones (female) larger than pollen cones. • The female cone has a pair of ovules at bases of seed cone scales. • Pollen cones (male strobili) consist of papery or membranous scales. The Female Cone • Inside the female cone, we find ovules. These ovules are exposed. • Inside the ovules, we find the female gametophyte or nucellus (in angiosperms, this was known as the embryo sac). • Inside the nucellus, we find the egg cell (megaspore). The Male Cone • Pollen cones produce pollen grains Reproduction cont. Seed cones take two years to mature. First year: • Pollen grains catch on sticky pollen drops oozing out of micropyle (ovule opening). • Pollen grain produces pollen tube that grows through nucellus. Two sperms produced in pollen tube. • Ovule develops. Second year: • Female gametophyte inside the ovule and archegonium mature. • Pollen tube arrives at archegonium. • One sperm unites with egg, forming zygote. Other sperm degenerates. • Embryo nourished by female gametophyte. • Integument becomes seed coat. Pine Reproduction: Phylum Ginkgophyta • Phylum Ginkgophyta – Ginkgo (maidenhair trees). Only one living species and it only exists in cultivation. • Notched, broad, fan-shaped leaves on short, slow-growing spurs. • No midrib or prominent veins. Hair-like veins branch dichotomously. • Deciduous Phylum Ginkgophyta • Life cycle similar to pines but male and female structures on separate trees. • Seeds enclosed in fleshy seed coat with nauseating odor. Male strobili (cones) Seeds and leaves Phylum Cycadophyta – The Cycads • Slow-growing plants of tropics and subtropics • Tall unbranched trunks • Crown of large pinnately divided leaves • Life cycle similar to conifers. Male and female plants. Pollination sometimes by beetles. Male cycad Female cycad Phylum Gnetophyta • Unique among the gymnosperms in having vessels in the xylem. • Ephedra: Shrubby plants of drier regions of southwestern North America. • Welwitschia: Only one species, confined to deserts of southwestern Africa. • Gnetum: Vine-like plants with broad leaves confined to the tropics Human Relevance of Gymnosperms • Conifers • Lumber: Masts in sailing vessels, crates, boxes, matchsticks, furniture, telephone poles, railroad ties, mine timbers, building lumber. • Paper making • Turpentine and rosin (both from resin) • Fuel. • Edible inner bark and needles of white pine, and seeds of nearly all pines • Ornamentals • Pharmaceuticals (taxol for ovarian cancer from yew trees) • Other Gymnosperms • • Ginkgo: • Seeds for food (after seed coat removal) • Ginkgo extracts to increase blood circulation Ephedra: Drug ephedrine for respiratory problems from a Chinese species Review • Introduction • Phylum Pinophyta – The Conifers • Other Gymnosperms • • Phylum Ginkgophyta – Ginkgo • Phylum Cycadophyta – The Cycads • Phylum Gnetophyta – The Gnetophytes Human Relevance of Gymnosperms • Conifers • Other Gymnosperms