Non-Vascular Plants and Ferns Evolution of Land Plants • Land plants evolved from green algae • The green algae called charophyceans are the closest relatives of land plants • Comparisons of both nuclear and chloroplast genes – Point to charophyceans as the closest living relatives of land plants (a) Chara, a pond organism 10 mm (b) Coleochaete orbicularis, a diskshaped charophycean (LM) 40 µm Origin and Diversification of Plants • Fossil evidence indicates that plants were on land at least 475 million years ago • Whatever the age of the first land plants those ancestral species gave rise to a vast diversity of modern plants Plant Evolution Land plants Vascular plants Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Origin of seed plants (about 360 mya) Angiosperms Seed plants Gymnosperms Pterophyte (ferns, horsetails, whisk fern) Lycophytes(club mosses, spike mosses, quillworts) Seedless vascular plants Mosses Hornworts Liverworts Charophyceans Bryophytes (nonvascular plants) Bryophytes • Life cycles of mosses and other bryophytes are dominated by the gametophyte stage • Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants – Liverworts, phylum Hepatophyta – Hornworts, phylum Anthocerophyta – Mosses, phylum Bryophyta Bryophytes Gametophore of female gametophyte LIVERWORTS (PHYLUM HEPATOPHYTA) Plagiochila deltoidea, a “leafy” liverwort Foot Seta Marchantia sporophyte (LM) HORNWORTS (PHYLUM ANTHOCEROPHYTA) An Anthoceros hornwort species Sporophyte Sporangium 500 µm Marchantia polymorpha, a “thalloid” liverwort MOSSES (PHYLUM BRYOPHYTA) Polytrichum commune, hairy-cap moss Sporophyte Gametophyte Gametophyte Liverworts • Have no true roots or shoots • Non- vascular • Require water to reproduce • Have no or very little leaf structure • Cannot live in sporophyte form Hornworts • Free-floating aquatic plant, or land plant • No vascular tissue • No true leaves or roots • Can live in both gametophyte and sporophyte forms Mosses • Land plant • Most have no vascular tissue • Majority to life spent in gametophyte • Need water to breed • No leaves or roots • Sporophytes are capsules on stalks Vascular Plants • Vascular plants have two types of vascular tissue – Xylem and phloem • Xylem – Conducts most of the water and minerals – Includes dead cells called tracheids • Phloem – Distributes sugars, amino acids, and other organic products – Consists of living cells Vascular Plants • Vascular plants have roots – Are organs that anchor vascular plants – Enable vascular plants to absorb water and nutrients from the soil – May have evolved from subterranean stems • Vascular plants have leaves – Leaves are organs that increase the surface area of vascular plants, thereby capturing more solar energy for photosynthesis Vascular Plants • Two types of vascular plants: seedless and seeded • Seedless vascular plants form two phyla – Lycophyta, including club mosses, spike mosses, and quillworts – Pterophyta, including ferns, horsetails, and whisk ferns and their relatives • Modern species of lycophytes are relics from a far more eminent past – Are small herbaceous plants • Ferns – Are the most diverse seedless vascular plants Seedless Vascular Plants LYCOPHYTES (PHYLUM LYCOPHYTA) Strobili (clusters of sporophylls) Isoetes gunnii, a quillwort Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss PTEROPHYTES (PHYLUM PTEROPHYTA) Psilotum nudum, a whisk fern Equisetum arvense, field horsetail Athyrium filix-femina, lady fern Vegetative stem Strobilus on fertile stem WHISK FERNS AND RELATIVES HORSETAILS FERNS Ferns • Seedlsess vascular plants but do not have seeds – Common in shady areas, diverse in the tropics – Have flagellated sperm that require water to reach the eggs Alternation of Generations • The seed plant life cycle contains both haploid and diploid stages – Diploid individuals are called sporophytes – Haploid individuals are called gametophytes • Does not happen in algae • May have evolved as an adaptation to harsh environments – Haploid cells divide into a cluster of cells before meiosis Alternation of Generations Gametophytes (male and female) n Spores n Meiosis Gametes (sperm and eggs) n HAPLOID Fertilization DIPLOID Zygote 2n Sporophyte 2n Dominant Gametophyte • Mosses have a dominant gametophyte stage 5 Mitosis and Sperm (n) (released from their gametangium) development Spores (n) 1 Gametangium containing the egg (n) (remains within gametophyte) Gametophytes (n) Egg HAPLOID DIPLOID Meiosis Sporangium Fertilization Stalk 2 4 Zygote (2n) Gametophyte (n) 3 Mitosis and development Sporophytes (growing from gametophytes) Dominant Sporophyte • Most plants have a dominant sporophyte stage 5 Sperm (n) Mitosis and development Spores (n) 1 Gametophyte (n) (underside) Egg (n) Meiosis Sporangia HAPLOID DIPLOID Fertilization 2 4 Zygote (2n) 3 Mitosis and development Sporophyte (2n) New sporophyte growing out of gametophyte Seeded Vascular Plants • Gymnospermsconifers, cycads, and ginkgo • Angiospermsflowering plants