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Nonvascular Plants • Believed to Have Evolved from Green-Algae

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Nonvascular Plants • Believed to Have Evolved from Green-Algae Nonvascular Plants • Believed to have evolved from green-algae – Chlorophylls a & b and cartenoids – Store starch within chloroplasts – Cell wall made up mostly of cellulose • Major adaptations in going from water to land – A protective sterile jacket to protect reproductive structures, antheridia and archegonia – Development of a waxy cuticle – Development of stomata for gas exchange on sporophytes Nonvascular Plants • Classification – three major divisions – grouped together because of several similarities – Gametophyte nutritionally independent from the sporophyte, but the sporophyte is permanently attached to the gametophyte – The gametophyte is the the conspicuous generation – Possess rhizoids for anchoring but not absorption – Sperm requires water to swim to the egg – Possess a venter (surrounds the egg), neck canal cells that disintegrate and form a tube for sperm to follow to fertilize the egg Nonvascular Plants – Antheridium surrounded by a one cell layer thick sterile jacket – Spermatogenous cells form biflagellated sperm – Zygote developes within the archegonium – Archegonium expands to form a calyptra Division Bryophyta: Mosses • Gametophyte Generation – Leafy, upright, leaves arranged in a spiral fashion – Possess multicellular rhizoids for anchoring – Leaves, gametophores, usually one cell thick – not true leaves nor ancestors of true leaves Division Bryophyta: Mosses – Stems • Very little in the way of differentiation • possess a central area of conducting cells composed of hydroids and leptoids – hydroids – tracheid like cells, dead, empty, carry water and nutrients – leptoids – like sieve tubes, transport sugars, lack nuclei, many plasmodesmata – Antheridia frequently found in splash cups – Gametes are produced either in leaf axils or at the tips Division Bryophyta: Mosses • Sporophyte – Can take up 6 – 18 months to develop – Associated with the gametophyte – Sporangia typically associated with a stalk, seta – Possess stomates with only one guard cell – When young are photosynthetic but lose this Division Bryophyta: Mosses – Spore dispersal • Calyptra (archegonial tissue) dies, dries, and falls off, taking with it the operculum • Loss of opercululum exposes the periostome, which change shape depending upon humidity, gradually releasing spores • Each capsule up to 50 million spores Division Bryophyta: Mosses • Metabolism and Ecology – Very prone to desiccation – several adaptations have evolved to accommodate for this • Grow in very moist habitats or dry areas with microhabitats, no need for vascular tissues • Can become dormant during dry spells • Frequently grow in dense clumps to trap moisture – Some can thrive at very low temperatures – Can grow on very hard, dense surfaces, not roots – Play a role in soil production because of acids produced Divison Hepatophyta: Liverworts • 8500 species • Diverse • Inconspicuous, but may form large mats • Some consider them the simplest of the plants because they have: – Conducting tissue – A cuticle – Stomates • In most the gametophyte is formed by the germination of a spore • Divided into two groups Divison Hepatophyta: Liverworts – Thallose Liverworts • Moist, cool, shaded environments • Thallus multicellular with upper cells containing chlorophyll, lower cells colorless • Upper surface lacks stomates but does have pores • Marchantia – very common – Dichotomously branching gametophyte – Gametangia located on gametophores – Gametophytes are unisexual, easily seen Divison Hepatophyta: Liverworts • Gametophyte Generation – Spore germinates into a small proonematal structure – Small rhizoids on undersurface – Can be either uni or bisexual (Marchantia unisexual) » Male - Antheridiophores Divison Hepatophyta: Liverworts » Female - archegoniophores Divison Hepatophyta: Liverworts • Sporophyte Divison Hepatophyta: Liverworts – Leafy Liverworts • About 6000 species • Found in tropics and subtropics (warm and wet) • Branched forms form mats • Leaves only one cell thick, usually forming two rows on each side and one colorless one on underside Division Anthocerotophyta: Hornworts • Small group, only 6 genera • Most common genus, Anthoceros – Only one chloroplast – Each chloroplast has a pyrenoid – Gametophyte appears as a rosette • Multicellular with mucilage between cells • Within this mucilage can be found the cyanobacteria, Nostoc, which is nitrogen fixing • Can be bi or unisexual – Archegonia found sunken on the dorsal surface – Antheridia clustered within chambers Division Anthocerotophyta: Hornworts Division Anthocerotophyta: Hornworts – Sporophyte.
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