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8/28/2011 Ch 16 Bryophytes Bryophytes • Consist of liverworts, hornworts, and mosses. • Often grow in moist conditions – Not N t relegated l t d tto these th only l • Large constituent of carbon storage • Sensitive to air pollution – Often absent in high pollution areas 1 8/28/2011 Characters • Characteristics that distinguish bryophytes from charophytes: – Male and female gametangia • Antheridia & archegonia with protective sterile jacket layer. – Retention of zygote and embryo (i.e., sporophyte within the archegonium or the female gametophyte). – Multicellular diploid sporophyte – Multicellular sporangia – Meiospores containing sporopollenin – Tissues produced by apical meristem Structure & Reproduction • Hornworts & Liverworts described as: – “thalloid” b/c gametophytes are thalli. • Not differentiated into roots, leaves, and stems • Cells are interconnected by plasmodesmata. 2 8/28/2011 Bryophyte sperm • Many bryophytes reproduce asexually– Small pieces of tissue produce an entire gametophyte • Liverworts & mosses – Gemmae • Multicellular bodies that give rise to new gametophytes. Sexual reproduction • Production of antheridia & archegonia – On separate male or female gametophytes – Spherical or elongated antheridium is commonly stalked stalked. • Sterile jacket layer that surrounds numerous spermatogenous cells. • ‘jacket’ layer is sterile – Cannot produce sperm – Each spermatogenous cell forms a single biflagellated sperm that must swim through water to reach the egg; located inside the archegonium. 3 8/28/2011 • Venter – Encloses a single egg • Neck canal cells – Disintegrate when the egg is mature which forms a fluid-filled tube through which the sperm swim to the egg. – Chemicals are released that attract sperm. – Zygote is nourished by sugars, amino acids; • Known as matrotrophy • Matrotrophy fuels production of diploid sporophytes (like the placenta of plants). Embryophytes (synonym for plants) • Throughout evolutionary history sporophytes have become increasingly larger than gametophyte generation. • Sporophytes of hornworts & mosses have stomata – Bordered by guard cells (which resemble stomata of vascular cells). Sporopollenin • Bryophyte spores are impregnated with sporopollenin – Decay & chemical resistant bipolymer • Spores germinate to form: 1. Protonemata 2. Gametophytes & Gametangia 4 8/28/2011 Byrophytes: 3 phyla • Liverworts – Hepatophyta • Hornworts – Anthocerophyta A th h t • Mosses – Bryophytes Liverworts: Hepatophyta • ~ 6,000 spp. • Small & inconspicuous • Named ‘liverwort’ because of the liver shaped h d outline tli off th the gametophyte t h t iin some genera. • Most gametophytes develop from spores. – Some form a protonema-like filament of cells from which a gametophyte develops. Three major types of liverworts • Differentiated on basis of structure and grouped into two clades. 5 8/28/2011 Complex Thalloid Liverworts • Riccia, Ricciocarpus, and Marchantia • Found on moist shaded banks. • Thallus is 30 cells thick at midrib – Upper (dorsal) portion is chlorophyll rich – Lower (ventral) portion bears rhizoids & scales Riccia & Ricciocarpus • Sporophyte structure of these is simplest seen in liverworts. • Ricciocarpus grows in water or damp soil – Bisexual (both sex organs arise on same plant) – Riccia gametophytes • Unisexual or bisexual • Sporophytes are deeply embedded – Once gametophyte containing sporophytes dies • Spores are liberated System of branching gametophytes in Riccia. Sporophyte embedded within the gametophyte. (spherical capsule) 6 8/28/2011 Marchantia • • • • • Most familiar liverwort Gametangia borne on gametophores. Gametophytes are unisexual Antheridia borne on antheridiophores. antheridiophores Archegonia are borne on archegoniophores. • Sproangium contains elaters – Elongate cells which have helically arranged hygroscopic wall thickenings. Archegonia of Marchantia Antheridia of Marchantia Mature spores (red) and elaters (green strands) from a capsule of Marchantia. 7 8/28/2011 Marchantia reproduction • Fragmentation is principle asexual method • Another widespread mechanism – Production of gemmae • In Marchantia the gemmae are produced in cuplike structures – Gemmae cups • Gemmae are dispersed primarily by splashed of rain. Marchantia gametophytes. Gemmae cups containing gemmae. Longitudinal section of gemmae cup 8 8/28/2011 Leafy liverworts • 4,000 of the 6,000 species in phylum hepatophyta. • Abundant in tropics & sub-tropics • Leaves L consist i t off single i l llayer off undifferentiated cells. • Two rows of equal sized leaves & third row of smaller leaves along lower surface of gametophyte. • Antheridia generally occur on short side branch with modified leaves called: – Androecium • Archegonium & developing sporophyte surrounded by: – Perianth Gametophyte with attached sporophytes Sporangium p g splits, and spores released 9 8/28/2011 Hornworts: Anthocerophyta • 100 spp. • Anthoceros is most abundant • Hornwort gametophytes superficially resemble bl those th off thallose th ll li liverworts. t • Gametophytes are often rosette-like – Most are unisexual • Sporophytes of Anthoceros – Have foot & long capsule (sporangium) 10 8/28/2011 Mosses: Bryophyta • Consists of three classes – Sphagnidae, Andreaeidae, & Bryidae • Bryidae 9,500 spp. Peat Mosses: Sphagnidae • One large genus – Sphagnum – 400 spp • Distributed Di t ib t d worldwide ld id – Commercially & Economically important Sexual Reproduction • Formation of antheridia & archegonia – Occurs at ends of special branches at the tips of the gametophyte. – Fertilization occurs in late winter • Four months later, mature spores are discharged from sporangia. 11 8/28/2011 • Gametophyte with many attached sporophytes. Dehiscence has occurred Capsule dries & contracts Explosion of spores Compression of trapped gas Features that distinguish Sphagnidae from other mosses • Unusual protonema Leafy gametophyte • Peculiar morphology of gametophyte • Explosive operculum Plate-like protonema 12 8/28/2011 Sundberg 2010: Annals of Botany 105: 291-300 • Sphagnum has superior antiseptic & absorptive properties. – Used as diaper material by native peoples and in WWI as dressings for wounds wounds. Worldwide importance • Peatlands occupy > 1 % of earth’s surface. Area of peatland (KM sq) % peatland Africa 58,534 0.18 Asia 1,523,287 1.06 Australia, New Zealand, the Pacific and Antartica 8,009 0.04 North, Central and South America 2,050,746 4.83 13 8/28/2011 http://www.ramsar.org/pictures/types-peat-nz-waituna350.jpg http://www.google.com/imgres?q=close+up+of+peat&hl=en&client=firefox-a&hs=I8k&sa=X&rls=org.mozilla:enUS:official&biw=1680&bih=944&tbm=isch&prmd=ivns&tbnid=16E2Iev2P00mM:&imgrefurl=http://www.flickr.com/photos/newtosandiego/4536278778/&docid=mb6fzlMgeqAu8M&w=500&h=332&ei=_v1LT sDhCY2EsgL87PHHCA&zoom=1 • Store large amounts of organic carbon – 400 gigatons (400,000,000,000) • Global warming may result in oxidation of peatland carbon: – Further increasing CO2 levels and global temperatures 14 8/28/2011 Granite mosses: Andreaeidae • Two genera: – Andreaea & Andreaeobryum • Andreaea consists of 100 spp. – Mountainous M t i & arctic ti regions i ((often ft on granite it rocks) • Andreaeobryum single species – Northwestern Canada & Alaska – Grows on calcareous rocks http://www.teara.govt.nz/files/p10768au.jpg 15 8/28/2011 “True Mosses”: Bryidae • Branching filaments of protonemata have single row of cells & resemble filamentous green algae: – Mosses have slanted cross walls walls. Specialized tissues for water & food conduction • Stems of gametophytes & sporophytes have central strand of waterconducting tissue – Hadrom • Water-conducting cells – Hydroids • Food conducting cells – Leptoids • Food conducting tissue – leptom 16 8/28/2011 Moss sexual reproduction • Similar to horn & liverworts – Male & female gametangia – Unbranched matrotrophic sporophyte – Specialized spore dispersal process • Gametangia produced by leafy gametophytes. – Unisexual or bisexual – Sperm from antheridia discharged into a drop of water in splash cups. – Insects may also carry drops of water rich in sperm from plant to plant. 17 8/28/2011 • Sporophytes are borne on gametophytes – Capsules take 6 to 18 mo. to mature – Sporophyte cells contain chloroplasts • Conduct photosynthesis • As A ages loses l ability bilit tto photosynthesize h t th i • Spore dispersal results from bursting of operculum – Reveals a ring of teeth known as peristome • Asexual reproduction occurs by fragmentation. 18 8/28/2011 Growth patterns of moss • Two forms – Cushiony (gametophytes are erect & a little branched- terminal sporophytes) – Feathery (highly branched; sporophytes are borne laterally). • Feathery growth is found on mosses that hang from branches: – Referred to as epiphytes http://2.bp.blogspot.com/_JHKjXsX0KEk/SRd77opai1I/AAAAAAAACQE/bqmz8Q984mE/s1600/moss-laden%2Btrees.jpg 19 8/28/2011 Summary • Embryophytes evolved from Charophytes. • Bryophytes: Liverworts, Hornworts, & Mosses • Bryophytes B h t differ diff from f one another th by b the th presence/absence of stomata & conducting tissues & types of meristems. • Ecologically important 20