Topic 12: Evolution of Plants

Vocabulary flashcards covering the evolutionary origins, key terrestrial adaptations, life cycle stages, and taxonomic diversity of land plants.

Embryophyta (Land Plants)

The monophyletic clade of land plants characterized by the retention of a multicellular, diploid embryo within the maternal tissues; informally referred to as plants.

Archaeplastida

The eukaryotic supergroup that includes Kingdom Plantae, whose members descended from an ancient heterotrophic protist that acquired chloroplasts through the primary endosymbiosis of a cyanobacterium.

Primary Endosymbiosis

The evolutionary event in which a heterotrophic eukaryotic host engulfed a photosynthetic cyanobacterium, giving rise to chloroplasts containing chlorophyll $a$ and $b$ in the plant lineage.

Charophytes

Freshwater green algae identified by nuclear, chloroplast, and mitochondrial DNA comparisons as the closest living relatives of land plants.

Zygnema

A genus of filamentous freshwater charophyte algae that, along with related taxa, represents the closest living charophyte relative of land plants.

Streptophyta

The clade comprising charophyte green algae and embryophytes (land plants), united by shared derived cellular features such as rings of cellulose-synthesizing proteins.

Cellulose-Synthesizing Protein Rings

Circular arrays of proteins embedded in the plasma membrane of charophytes and land plants that synthesize and deposit cellulose microfibrils in the cell wall.

Sporopollenin

A durable, cross-linked organic polymer resistant to enzymatic degradation, UV light, and desiccation that encases charophyte zygotes and the outer walls of plant spores and pollen grains.

Cuticle

A waxy protective layer covering the epidermis of aerial plant organs that minimizes water loss and guards against microbial infection.

Stomata

Specialized microscopic pores in the epidermis of leaves and stems that facilitate photosynthetic gas exchange and regulate evaporative water loss.

Guard Cells

Specialized epidermal cells that flank each stoma and regulate its opening and closing to balance carbon dioxide uptake against water loss.

Xylem

Vascular tissue composed of dead, lignified, microscopic tubular cells that conducts water and dissolved minerals upward from roots to shoots.

Lignin

A complex phenolic polymer that strengthens and waterproofs the cell walls of xylem elements, providing mechanical rigidity to support vertical growth.

Phloem

Vascular tissue consisting of living cells arranged into tubes that transport sugars, amino acids, and other organic products of photosynthesis throughout the plant.

Alternation of Generations

A reproductive life cycle characteristic of plants that alternates between a multicellular haploid gametophyte ($n$) stage and a multicellular diploid sporophyte ($2n$) stage.

Sporophyte

The multicellular diploid ($2n$) generation in plants that develops from a zygote by mitosis and produces haploid spores through meiosis for aerial dispersal.

Gametophyte

The multicellular haploid ($n$) generation in plants that produces haploid gametes via mitosis and is specialized for fertilization.

Placental Transfer Cells

Specialized maternal cells featuring extensive wall ingrowths that facilitate the transport of nutrients from the parent gametophyte to the dependent embryo.

Sporangia

Multicellular reproductive organs on the diploid sporophyte in which diploid sporocytes undergo meiosis to generate walled, haploid spores.

Sporocytes

Diploid mother cells within sporangia that undergo meiosis to produce haploid spores.

Apical Meristems

Localized regions of actively dividing, undifferentiated cells at the growing tips of roots and shoots that sustain continuous primary elongation.

Cooksonia

An extinct genus of early land plants known from fossils dating to approximately $425\text{ mya}$, exhibiting primitive sporangia on leafless branching stems.

Bryophytes

An informal term referring to nonvascular land plants (liverworts, mosses, and hornworts) that lack specialized vascular conducting tissue and do not form a monophyletic group.

Lycophytes

A clade of seedless vascular plants comprising club mosses, spikemosses, and quillworts, with approximately $1{,}200$ extant species.

Monilophytes

A clade of seedless vascular plants—also called pteridophytes—encompassing ferns, horsetails, and whisk ferns, comprising approximately $12{,}000$ extant species.

Gymnosperms

A major clade of vascular seed plants whose seeds are not enclosed in protective ovary chambers, exemplified by conifers, cycads, ginkgo, and gnetophytes.

Angiosperms (Phylum Anthophyta)

Flowering vascular plants that produce seeds enclosed within protective fruits; with approximately $290{,}000$ extant species, they constitute roughly $89\%$ of all living plants.

Rosa acicularis

The wild rose, a flowering seed plant (angiosperm) recognized as Alberta's official floral emblem.

Pinus contorta

The lodgepole pine, a gymnosperm conifer recognized as Alberta's official provincial tree.

Phylum Hepatophyta

The nonvascular bryophyte phylum comprising liverworts, containing approximately $9{,}000$ known living species.

Phylum Bryophyta

The nonvascular plant phylum comprising true mosses, containing approximately $13{,}000$ known living species.

Phylum Anthocerophyta

The nonvascular plant phylum comprising hornworts, containing approximately $225$ known living species.