NONVASCULAR AND SEEDLESS VASCULAR PLANTS The earliest plants grew in areas like the coastal mud flats of the Devonian (410 million years ago): The non-vascular : Moss (1) alongside vascular : Cooksonia (2), Rhynia (3), Zosterophyllum (4), Drepanophycus (5). The beginning of the Carboniferous had a more uniform, tropical, and humid climate throughout the year than exists today. Seasons, if any, were indistinct. The number of plants during the Carboniferous became more numerous. Vascular plants began to dominate the landscape and gymnosperm-like plants began to appear. Angiosperms would appear much later. Early Vascular Plants a. Evolved from Charophytes, a group of green algae b. Cooksonia oldest vascular plant fossil ; Rhynia c. Late Silurian (414 - 408 million years BP) d. No roots or leaves e. Vascular plants dominated by the Devonian (408 - 362 million BP) Plant Adaptations a. Development of a 1) vascular system: xylem and phloem, 2) ground tissues: comprise the main plant body, and 3) dermal tissue: provide protective covering to plants b. Developed a waxy cuticle c. Upright growth habit; lignin (for structure and conduction) and cellulose d. Stomata for gas exchange (O2, CO2, H2O) e. Sex organs are multicellular gametangia f. Fertilization of egg develops into an embryo g. Roots evolved from underground stems Four Major Groups of Plants and Their Respective Phyla Bryophytes- nonvascular; reproduce via spores, seedless plants; includes the mosses, liverworts, and hornworts Phylum Bryophyta (Mosses) Phylum Hepaticophyta (Liverworts) Phylum Anthocerophyta (Hornworts) Seedless Vascular Plants- vascular plants which are seedless, use spores in reproduction; includes the ferns and fern allies Phylum Psilophyta (Whisk ferns) Phylum Lycopodophyta (Club Mosses) Phylum Sphenophyta (Horsetails) Phylum Pterophyta (Ferns) Gymnosperms- vascular, naked seed producing plants; includes conifers, cypress, cedars, cycads, etc. Phylum Cycadophyta (Cycads) Phylum Ginkgophyta (Ginkgo) Phylum Coniferophyta (Conifers) Phylum Gnetophyta (Welwitschia) Angiosperms- vascular plants, producing protected seed; includes all flowering plants Phylum Anthophyta (Flowering plants) Class Dicotyledones Class Monocotyledones Class Magnoliids Bryophytes- nonvascular; reproduce via spores, seedless plants; includes the mosses, liverworts, and hornworts Phylum Anthocerophyta (Hornworts) Phylum Hepaticophyta (Liverworts) Phylum Bryophyta (Mosses) It is now widely accepted (from morphological and molecular work) that a group of green algae called the charophytes represent the sister group to land plants. Homosporousone spore type produced and released) Hetrosporoustwo spore types produced one developing into a male gametophyte, the other into a female gametophyte Sporophyte Gametophyte All plants have alternation of generations. There is an evolutionary trend from a dominant autotrophic (selffeeding) gametophyte and a nutritionally dependent sporophyte to a dependent gametophyte and a dominant autotrophic sporophyte. This is exemplified by exploring the life cycles of a moss, a fern, and an angiosperm. Bryophytes- (9000 Mosses), (6000 Liverworts) and (100 Hornworts) a. Have no conductive tissues, thus no way to efficiently assimilate photosynthates or minerals; since they are reliant on diffusion, they are typically very small b. Three distinctive phyla c. Absorptive structures called rhizoids; “leaflike” blades/leaves d. Typically separate male and female gametophytic plants; sperm must swim through a thin film of water to fertilize the egg; a diploid zygote forms and grows into a mature moss sporophyte; spores will be released from the sporophyte and will germinate to form a protonema which further develops into the gametophyte e. The gametophytic generation is the dominant form of the life cycle f. Liverworts may exhibit a leafy morphology or a thalloid (thallus) body form; some reproduce asexually using gemmae cups containing gemma Life cycle of a moss. The sporophyte generation is dependent on the photosynthetic gametophyte for nutrition. Cells within the micro- and megasporangia undergo meiosis to produce male and female spores, respectively. These spores divide mitotically to produce multicellular male and female gametophytes. Differentiation of the growing tip of the gametophyte produces antheridia in males and archegonia in females. The sperm and egg are produced in the antheridia and archegonia, respectively. Sperm are carried to the archegonia in water droplets. After fertilization, the sporophyte generation develops in the archegonium and remains attached. Seedless Vascular Plants (11,000 Ferns), (Club Mosses 1,000), (Horsetails 15) and (Whisk Ferns 12) Seedless Vascular Plants- plants which have distinct tissues for conducting water and nutrients throughout the plant; use spores for reproduction instead of seeds; there are four phyla of SVP 1. Phylum Psilophyta (Whisk ferns) 2. Phylum Lycopodophyta (Club Mosses) 3. Phylum Sphenophyta (Horsetails) 4. Phylum Pterophyta (Ferns) Whisk Ferns A. Exhibits a dichotomous branching pattern B. Stems are the main photosynthetic organ C. Most are extinct; very primitive vascular plant Club Mosses A. Once dominant plants in the landscape, 300my ago B. Strobilus are present to bear spores C. Some are homosporous, some are heterosporous; If heterosporous, male microspores (n) will be produced along with female megaspores (n); once shed, these spores will develop into male and female gametophytes which will produce sperm and egg respectively; when the egg is fertilized a sporophyte (2n) will form; within the strobilus spores form and the process repeats Horsetails A. Once dominant plants in the landscape, 300my ago B. True roots, stems and small leaves (reduced megaphylls); hollow jointed stems impregnated with silica; green stem main photosynthesizing part C. Reproductive branches bear a terminal cone-like strobilus D. Life cycle is similar to fern life cycle; also requires water Ferns a. Conductive tissues present; xylem and phloem!! Thus may be larger, and allowed for true leaf evolution! b. Two Basic Leaf Types: 1) Microphyll- possess a single vascular strand and are typically small and 2) Megaphyll- possess more than one vascular strand and are typically larger than microphylls; webbing effect seen c. Sporophyte is the dominant generation! Consists of roots, rhizomes and fronds; fiddleheads are young fronds; sori appear on the fronds and house spores d. Spores (n) germinate into a prothallus (n) which will produce eggs (n) in the archegonium and sperm (n) in the antheridium; they combine to form a zygote (2n); the zygote grows into a young sporophyte (2n); the mauture sporophyte of most ferns produce only one type of spore (homosporous- one spore type produced and released); some are hetrosporous, that is they produce two spore types, one developing into a male gametophyte, the other into a female gametophyte Water is required for the sperm to use as a medium to swim to the egg Life cycle of a fern. The sporophyte generation is photosynthetic and is independent of the gametophyte. Meiosis of the tissue within the sporangia yields a haploid spore that divides to produce a heartshaped gametophyte that differentiates both archegonia and antheridia on one individual. The gametophyte is photosynthetic and independent, although it is reduced in size relative to the sporophyte. Fertilization takes place when water is available for sperm to swim to the archegonia and fertilize the eggs. The Sporophyte continues to grow while the Gametophyte dies.