Aquatic Plants: Non-Vascular Plants and Ferns

Evolution of Plants Plants are thought to have 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 Chara, a pond organism (a) 10 mm Coleochaete orbicularis, a disk- shaped charophycean (LM) (b) 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 Bryophytes (nonvascular plants) Seedless vascular plants Seed plants Vascular plants Land plants Origin of seed plants (about 360 mya) Origin of vascular plants (about 420 mya) Origin of land plants (about 475 mya) Ancestral green alga Charophyceans LiverwortsHornworts Mosses Lycophytes(club mosses, spike mosses, quillworts) Pterophyte (ferns, horsetails, whisk fern) Gymnosperms Angiosperms

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

Alternation of Generations HAPLOID Meiosis Spores n Mitosis Gametophytes (male and female) n Mitosis Gametes (sperm and eggs) n Fertilization Zygote 2n Mitosis DIPLOID Sporophyte 2n

Dominant Gametophyte Mosses have a dominant gametophyte stage Sperm (n) (released from their gametangium) Gametangium containing the egg (n) (remains within gametophyte) Egg Fertilization Zygote (2n) Mitosis and development Sporophytes (growing from gametophytes) HAPLOID DIPLOID Gametophyte (n) Sporangium Stalk Meiosis Spores (n) 5 Mitosis and development Gametophytes (n)

Dominant Sporophyte Most plants have a dominant sporophyte stage Gametophyte (n) (underside) Sperm (n) Egg (n) Fertilization Zygote (2n) Mitosis and development New sporophyte growing out of gametophyte Sporophyte (2n) Meiosis Sporangia 5 Spores (n) Mitosis and development HAPLOID DIPLOID

Non Vascular 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 LIVERWORTS (PHYLUM HEPATOPHYTA) HORNWORTS (PHYLUM ANTHOCEROPHYTA) MOSSES (PHYLUM BRYOPHYTA) Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Foot Sporangium Seta 500 µm Marchantia sporophyte (LM) Plagiochila deltoidea, a “leafy” liverwort An Anthoceros hornwort species Sporophyte Gametophyte Polytrichum commune, hairy-cap moss Sporophyte 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 really ancient –Are small herbaceous plants Ferns –Are the most diverse seedless vascular plants

Seedless Vascular Plants LYCOPHYTES (PHYLUM LYCOPHYTA) PTEROPHYTES (PHYLUM PTEROPHYTA) WHISK FERNS AND RELATIVES HORSETAILS FERNS Isoetes gunnii, a quillwort Selaginella apoda, a spike moss Diphasiastrum tristachyum, a club moss Strobili (clusters of sporophylls) Psilotum nudum, a whisk fern Equisetum arvense, field horsetail Vegetative stem Strobilus on fertile stem Athyrium filix-femina, lady fern

Ferns 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

Land plants: Seeded Vascular Plants Gymnosperms- conifers, cycads, and ginkgo Angiosperms- flowering plants