Plant Diversity, Reproduction, and Evolution

Comprehensive practice flashcards reviewing non-vascular plants, seedless vascular plants, gymnosperms, and angiosperms, focusing on structural morphology, reproduction, alternation of generations, and macroevolutionary trends.

Primary Endosymbiosis

The evolutionary event in which a heterotrophic eukaryotic host engulfed a photosynthetic cyanobacterium, giving rise to the first chloroplast (plastid) and founding the Archaeplastida lineage.

Secondary Endosymbiosis

The process occurring independently and multiple times across protist lineages where a non-photosynthetic eukaryote engulfed a red alga or green alga that had already undergone primary endosymbiosis.

Brown Alga Body Plan

A multicellular, plantlike anatomy analogous to land plants consisting of a rootlike holdfast that anchors the organism, a stemlike stipe, and leaflike blades that carry out photosynthesis.

Gametic Meiosis

A sexual life cycle found in animals and some algae where meiosis produces haploid ($n$) gametes (sperm and egg) that fuse in fertilization to form a diploid ($2n$) zygote that develops into a multicellular diploid organism via mitosis.

Zygotic Meiosis

A sexual life cycle found in fungi and some protists where haploid individuals produce haploid gametes by mitosis, and the single-celled diploid ($2n$) zygote is the only diploid stage, immediately undergoing meiosis to yield haploid spores.

Sporic Meiosis (Alternation of Generations)

A life cycle found in land plants and some algae alternating between a multicellular diploid ($2n$) sporophyte that generates haploid spores by meiosis and a multicellular haploid ($n$) gametophyte that produces haploid gametes by mitosis.

Charophytes

The lineage of green algae that represents the closest living relative of land plants, sharing derived traits including rings of cellulose-synthesizing proteins, flagellated sperm structure, and formation of a phragmoplast.

Sporopollenin

A durable polymer found in plant spore walls and charophyte zygote walls that provides resistance to harsh conditions and prevents exposed cells from desiccation.

Embryophytes

The clade comprising land plants, characterized by the retention of a multicellular, diploid ($2n$) embryo that is dependent on and nourished by the maternal gametophyte tissue through placental transfer cells.

Apical Meristems

Localized regions of sustained cell division at the growing tips of plant roots and shoots that differentiate into the outer epidermis and various internal tissues.

Early Plant Fossil Evidence

Microscopic fossilized plant spores and tissues dating back to at least $470\text{ mya}$ to $450\text{ mya}$, with larger structural fossils such as sporangia (e.g., Cooksonia) appearing by $425\text{ mya}$.

Land Plant Evolutionary Milestones

The major evolutionary transitions marking the origin of land plants at approximately $470\text{ mya}$, the origin of vascular plants at approximately $425\text{ mya}$, and the origin of extant seed plants at approximately $305\text{ mya}$.

Bryophytes vs. Bryophyta

The term 'bryophytes' is an informal catch-all descriptor for a paraphyletic grade of all non-vascular land plants, whereas 'Bryophyta' is the formal taxonomic phylum specifically comprising mosses.

Protonema (plural: Protonemata)

A mass of green, branched, one-cell-thick filaments produced by a germinating moss spore that undergoes mitotic growth to develop one or more buds that form 'leafy' gametophores.

Rhizoids

Cellular filaments at the base of bryophyte gametophytes that serve to anchor the plant into the substrate; they lack vascular tissue and do not play a primary role in water or mineral conduction.

Antheridium (plural: Antheridia)

A multicellular male gametangium that produces and releases flagellated sperm cells into an external film of water.

Archegonium (plural: Archegonia)

A vase-shaped multicellular female gametangium that produces and retains a single non-motile egg cell and serves as the site of fertilization.

Moss Sporophyte Anatomy

A dependent, non-photosynthetic or semi-dependent structure consisting of a foot embedded in the gametophyte, an elongated seta (stalk), and a terminal capsule (sporangium) where haploid spores are produced via meiosis.

Peristome

A specialized ring of interlocking, tooth-like structures at the top of a moss capsule that gradually discharges and disperses spores under favorable atmospheric conditions.

Stomata Distribution in Bryophytes

Specialized gas-exchange pores present on the sporophytes of mosses (Bryophyta) and hornworts (Anthocerophyta), but completely absent in liverworts (Hepatophyta).

Archegoniophore

An elevated, umbrella-like gametophore branch in thalloid liverworts like Marchantia polymorpha that bears archegonia on its underside.

Sphagnum

A genus of moss ('peat moss') that forms extensive deposits of undecayed organic material (peat), functioning as a massive global carbon reservoir due to the low temperature, pH, and oxygen levels of peatlands inhibiting decay.

Lignin

A complex polymer embedded in the cell walls of vascular conducting tissues that provides structural rigidity, enabling vascular plants to grow taller to compete for sunlight.

Microphylls

Small, spine-shaped leaves supported by a single unbranched strand of vascular tissue; uniquely found in lycophytes and hypothesized to have evolved around $410\text{ mya}$ in the Early Devonian.

Megaphylls

Leaves with a highly branched vascular network, providing greater surface area for photosynthesis, which evolved in monilophytes and seed plants around $370\text{ mya}$ in the Late Devonian through the fusion of overtopping stems.

Sporophyll

A specialized modified leaf that bears sporangia, responsible for producing reproductive spores.

Sorus (plural: Sori)

A cluster of sporangia located on the abaxial (underside) surface of a fertile fern sporophyll.

Strobilus (plural: Strobili)

A cone-like aggregate structure formed by groups of sporophylls, found in lycophytes, horsetails (Equisetum), and gymnosperms.

Phylum Lycophyta

A lineage of seedless vascular plants consisting of spike mosses, quillworts, and club mosses, which possess microphylls and vascular tissue rather than true moss anatomy.

Phylum Monilophyta

A lineage of seedless vascular plants characterized by megaphylls and closer relation to seed plants, comprising ferns, horsetails (Equisetum), and whisk ferns (Psilotum).

Homospory

The condition of producing a single type of spore from one sporangium, which typically develops into a bisexual gametophyte capable of producing both sperm and eggs.

Heterospory

The condition of producing two morphologically and functionally distinct types of spores: smaller microspores that develop into male microgametophytes and larger megaspores that develop into female megagametophytes.

Archaeopteris

An extinct woody progymnosperm from approximately $385\text{ mya}$ that attained heights up to $20\text{ m}$ and exhibited heterospory but did not produce seeds.

Seed

A fertilized, mature ovule consisting of a multicellular embryonic sporophyte ($2n$) packaged alongside a nutritive food reserve within a protective seed coat.

Ovule

A plant structure consisting of a megasporangium (nucellus), a megaspore, and one or more protective integuments that develops into a seed following fertilization.

Integument

A layer of diploid ($2n$) maternal sporophytic tissue enclosing the megasporangium that hardens and differentiates into the protective seed coat after fertilization.

Pollen Grain

A structure that contains or directly represents the male gametophyte (microgametophyte), enclosed in a tough, sporopollenin-rich wall that enables sperm transfer without external water.

Gymnosperm

A seed plant producing 'naked seeds' that develop directly on the surfaces of open sporophylls or cone scales rather than enclosed inside ovaries or fruits.

Phylum Cycadophyta

An ancient gymnosperm lineage characterized by large cones and palmlike leaves that retains flagellated sperm despite producing seeds.

Phylum Ginkgophyta

A gymnosperm phylum represented today by a single extant species, Ginkgo biloba, characterized by fan-shaped leaves, high air-pollution tolerance, and flagellated sperm.

Phylum Gnetophyta

A gymnosperm phylum comprising three diverse genera: Gnetum (tropical trees and vines), Ephedra (arid-region shrubs yielding ephedrine), and Welwitschia (desert plants with huge straplike leaves).

Phylum Coniferophyta

The largest extant gymnosperm phylum, comprising cone-bearing woody trees such as pines, firs, and redwoods, predominantly evergreen and dominant across the northern boreal forest.

Gymnosperm Microgametophyte

A male gametophyte reduced to exactly four cells: one tube cell, one generative cell, and two sterile vegetative (prothallial) cells, having lost multicellular antheridia completely.

Aerodynamic Vortex Hypothesis

The hypothesis proposing that sterile bracts on female gymnosperm ovulate cones alter aerodynamics, generating a physical air vortex that draws windborne pollen grains into the cone scales toward the ovules.

Gymnosperm Seed Generations

The three distinct generations present within a mature gymnosperm seed: the parent sporophyte ($2n$) represented by the seed coat, the female gametophyte ($n$) providing the food reserve, and the new sporophyte ($2n$) embryo.

Phylum Anthophyta

The sole taxonomic phylum encompassing all angiosperms (flowering plants), characterized by flower production, fruits enclosing seeds, and double fertilization.

Floral Whorls

The four concentric rings of modified leaves forming a complete flower: the calyx (sepals), corolla (petals), androecium (stamens bearing anthers), and gynoecium (carpels enclosing ovules).

Double Fertilization

An autapomorphic process in angiosperms where one sperm nucleus fertilizes the egg to create a diploid ($2n$) zygote, while the second sperm nucleus fuses with the two polar nuclei of the central cell to produce triploid ($3n$) endosperm.

Embryo Sac

The mature female gametophyte (megagametophyte) of angiosperms, typically consisting of seven cells with eight haploid nuclei: three antipodal cells, two polar nuclei in a central cell, two synergids, and one egg cell.

Angiosperm Microgametophyte

The mature male gametophyte housed within an angiosperm pollen grain, reduced to exactly two cells: a tube cell and a generative cell that divides mitotically into two sperm nuclei.

Fruit

A mature plant ovary that encloses one or more fertilized seeds, functioning in the protection and environmental or animal dispersal of the seeds.

Dioecious vs. Monoecious

Dioecious plants have unisexual staminate and carpellate flowers located on separate individual plants ('two houses'), whereas monoecious plants bear both male and female reproductive flowers on the same individual ('one house').

Reduction of the Gametophyte

The macroevolutionary trend from dominant, free-living gametophytes in bryophytes to microscopic, dependent gametophytes in seed plants, culminating in a 2-celled microgametophyte and a 7-celled megagametophyte in angiosperms.

Sporocyte

A specialized diploid ($2n$) spore mother cell (a specific type of myocyte) located within a sporangium that divides by meiosis to produce four haploid ($n$) spores.