Seedless Plants

Evolutionary Order

ancestral green algae → bryophytes → lycophytes → pteridophytes → seed plants

What Are Plants?

multicellular autotrophs adapted for life on land; a few have lost ability to photosynthesize (many of those are parasitic); some mainly aquatic (but descended from land-adapted ancestors)

green algae is NOT a plant

Sporophyte vs Gametophyte Dominance

green algae: gametophyte dom

mosses: gametophyte dom

ferns: 50/50 ish (at another point in lecture she contradicts herself and says sporophyte dom)

gymnosperms: sporophyte dom

angiosperms: sporophyte dom

Streptophytes

land plants and their closest algal relatives

Charophycean Algae

apical meristems, when present, do not produce tissues; zygotes the only diploid cells; sporangia absent; spores lack sporopollenin walls

Embryophytes

apical-tissue-producing meristems; multicellular sporophytes; sporangia; sporopollenin-walled spores

Nonvascular Plants

bryophytes (liverworts, mosses, hornworts)

no lignified vascular tissue, no true roots, stems, or leaves; sporophytes unbranched; cannot grow independently of gametophytes

Vascular Plants

lignified vascular tissue; sporophytes branched and become independent of gametophytes

Seedless Vascular Plants

lycophytes (lycophyll leaves- small, simple) and pteridophytes (ferns- euphyll leaves- “true”, complex)

seeds absent; adventious roots present; embryonic roots absent

Seed Plants

seeds present; euphyll leaves; embryonic roots present

gymnosperms- flowers and fruits absent; seeds lack endosperm

angiosperms- flowers and fruits present; seeds possess endosperm at least early in development

Common Traits in Plants

tissues produced by apical meristems

spores with tough walls; sporopollenin coat on spores (chemically inert biological substance made of fatty acids, carotenoids, and phenolics)

spores produced in multicellular enclosures called sporangium

alternation of generations (haploid gametophyte; diploid sporophyte)

embryo (early stage of sporophyte) dependent on female gametophyte

Seedless Plants in the Past

bryophytes 500 million years ago started using CO2 and converting it into decay-resistant carbon compounds

History of Plants

evolutionary history of plants- comparisons of genes coding for phytochrome, rubisco, and tubulin

DNA indicates that land plants are most closely related to modern Charohycean green algae 

Fossil Evidence

fossils formed because plants produce decay-resistant polymers like sporopollenin, lignin, and cutin

Origin of Land-Adapted Plants - Bryophytes

transition to land more than 500 million years ago; widespread and abundant by 460 million years ago bryophytes are earlier

bryophytes earliest group to evolve- small plants, no branches, no true vascular tissues (no lignin in conducting vessels), biggest change was the fact that the began getting off the ground

Rise of Vascular Plants - Protracheophytes

protracheophytes were small, nonvascular branched sporophytes that evolved 400 million years ago but are now extinct

had only a true stem covered with cutin and stomata for gas exhange, but no roots or leaves

Rhynie Chert - Fossilized Plant

plant from early devonian period 410 million years ago; preserved due to silica rich water from volcanic spring

Aglaophyton

found in Rhynia; gametophyte and sporogrophyte are well-preserved in fossil; so well that life cycle is now known just from fossil record

prevascular plant; mycorrhizal symbiont

Descent with Modification - Sporophyte Origins

sporophyte may have originated when an algal ancestor acquired a mutation that delayed meiosis in the zygote until several mitotic divisions occurred 

Origin of Fern Leaves

lycophytes have small leaves with a single unbranched vein

branches begin to come together and form paddle-like structure which are the earliest structure of leaves (fern leaves also evolved from these)

Euphylls/Megaphylls

larger leaves with branches veins; these leaves apparently evolved from flattened branch stems

Bryophytes (Mosses, Liverworts, Hornworts)

gametophyte bodies are dominant and only one or few cells thick, enabling plants to absorb moisture directly from the environment; lack of well-developed vascular tissue limits their size

no true leaves; no vascular tissue

Rhizoids

thin extensions of epidermal cells that help anchor gametophyte to soil, but do not help absorb nutrients or transport water into other parts of plant

seen in bryophyte cross-section in lecture

Sporophytes

have a basal foot anchored in maternal gametophyte (archegonia), a seta (basically a stalk), and a sporangium capsule that produces spores

never grows independently from gametophyte; grows directly from it 

Bryophyte Reproduction

asexual reproduction: from little cup-like structures; production of gemmae- small pieces of tissue that break off and are dispersed by wind

Sexual Reproduction

fertilization leads to diploid zygote to diploid sporophyte; meiosis produces haploid spores then mature gametophyte; antheridia/archegonia haploid from mitosis

Bryophyte Ecological/Economical Importance

most grow on soil, rocks, and the surfaces of plants

moss can stay dry and still survive and then rehydrate; peat moss 

phenolic compounds absorb damaging UV light

Lycophytes (Club Mosses)

sporophyte dominant; vascular tissues present along with true roots, stems, and small leaves with single unbranched vein (lycophylls or microphylls)

sporangia may form cones similar to later gymnosperm cones

spores are oil rich- once used by photographers for flash

ex: selaginella

Lycophyte Reproduction

most are homosporous- produce a single type of spore that grows into a bisexual gametophyte that produces eggs and sperm

(similar to moss lifecycle)

Pteridophytes (Ferns, Horsetails, Whisk Ferns)

sporophyte dominant; vascular tissues is present along with true roots, stems, and large leaves (euphylls)

often have rhizomes (horizontal stems) with extensively branched veins

most are homosporous

Whisk Ferns (Psilotum)

tropical plants with no leaves or roots; fully photosynthetic stems grow upwards, branch and are green; yellow sporangia on stems

Horsetails (Equisetum)

tiny leaves but have branched veins (euphylls); spores are produced in sporangia that form a cone or strobilus; gametophytes are green and grow above ground

Fiddleheads

young fern leaves that develop in spirals that unfurl at specific point in growth

Sphagrnum Moss

plays important role in the cycling of carbon compounds; at risk due to global warming

peat moss acts as carbon sink

Sporophytes, Sori, Sporangia, & Spores

sporophyte: entire spore-producing plant (diploid)

sori: clusters of sporangia; can be in different patterns

sporangia: sac-like structures within sori where meiosis occurs to produce spores

spores: the individual, haploid