First Land Plants & Bryophytes

• Monophyletic: all organisms from a common ancestor
• paraphyletic: organisms descended from a common ancestor, but not including all the descendant groups (one might be left out)
• polyphyletic: do not share a common ancestor
• convergent evolution: unrelated, but similar in some characteristics
• water to land transition: 475 - 510 MYA BP
• ordovician: lots of life in sea, little on land (505-440 MYA BP)
• first land plants: probably in wet areas with high humidity , water loss was a major problem
• Features developed to cope with challenges of survival on land: compact multicellular body, cuticle, protected gamete and spore cells
• all land plants have: spores in sporangia, gametes in gametangia, and oogamy (large, non motile egg and small motile sperm - oogamous)
• charophyceae: fresh water green algae, most probable ancestors of land plants
• shared features of land plants & some charophyceae: pigments (chlorophyll a, chlorophyll b and cartenoids, phytochrome) , chloroplast features (well developed grand, starch stored in chloroplasts), cell walls containing cellulose, common features of mitosis, sporopollenin in some cells
• chlorophyll a is the primary photosynthetic pigment
• chlorophyll b and carotenoids are accessory photosynthetic pigments (manage energy load)
• phytochrome: light sensing pigment
• land plant life cycle has alternating generations (sporic meiosis ; between haploid and diploid)
• sporophyte (diploid individual) = spore bearing plant
• gametophyte (haploid individual)= gamete bearing plant
• all land plants are monophyletic (share a common ancestor)
• bryophytes: 3 phyla ~16,000 species, marchantiophyta (liverworts), Bryophyta (mosses), anthocerotophyta (hornworts)
• bryophytes are cryptograms ( greek: kruptos- hidden, gamos - marriage) . reproduction was not understood
• Similarities among the bryophytes: small, terrestrial (moist habitats), thin or no cuticle, alternation of multicellular generations, dominant gametophyte (haploid ), depend on water for sexual reproduction
• gametangia: a reproductive organ that houses and protects the gametes of a plant
• microgametangia = antheridia contain sperm cells
• megagametangia = archegonia contain eggs
• in liverworts & mosses: venter encloses an egg cell, sperm swim to egg via neck
• oogamous = large non motile egg (stays in archegonium), small motile sperm
• syngamy = fertilization forms a 2n zygote
• calyptra = a protective cap of gametophyte tissue that wholly or partially covers an immature capsule in many mosses
• Sporophyte (2n) in bryophytes: small, often temporary, little photosynthesis, obtains nutrients from gametophyte via placenta (transfer cells- specialized parenchyma) in "foot", unbranched, stalk = seta, capsule = sporangium
• bryophyte sporophyte forms a single, multicellular sporangium (capsule) with sterile jacket layer and internal sporogenous tissue
• sporogenous cells undergo meiosis forming spores (1n) in sporangium (most are homosporous = one kind of spore)
• spores disperse and germinate into protonema and new gametophyte grows from cluster of cells on protonema
• gametophytes can spread asexually from: detached pieces of gametophyte or protonema or gemmae (brood bodies)
• gemmae = a small cellular body or bud that can separate to form a new organism
• protonema: branched thread like structure that grows from moss spore and eventually develops into the moss plant