Plant Biology: Key Terms and Glossary

The separation layer at which a leaf or other organ is shed, leaving a scar in which the severed bundles can still be seen.

The cell that maintains a gymnosperm sieve cell, and that is not produced as that sieve cell's sister.

The living, protein-rich outer layer of a cereal endosperm, surrounding the starchy interior.

A nitrogen-containing secondary metabolite, usually built from amino acids, often bitter and used by the plant in defence rather than as a drug.

The land-plant life cycle, with a multicellular haploid generation and a multicellular diploid generation, spores made by meiosis and gametes made by mitosis.

The row of thick-walled cells on a leptosporangium that coils as it dries and flicks the spores out.

A jacketed organ in which sperm are formed by mitosis.

The proposal, not followed here, that the gnetophytes sit next to the angiosperms. Their place among the other gymnosperms is still open, and a second fusion in some of them does not leave a lasting triploid endosperm.

The Angiosperm Phylogeny Group classification scheme that sets out the major clades of flowering plants, not a ladder and not a taxon of "basal dicots".

A tip zone of dividing cells that adds length while tissues behind the tip differentiate.

Development of an embryo inside a seed from the mother's tissue, without fertilisation of the egg. It is neither selfing, which still has meiosis and fusion, nor vegetative spread, which makes no seed.

The continuous space of cell walls, and the water they hold, outside every plasma membrane, so a solute can travel there without entering a cell.

The branched hypha of an arbuscular mycorrhiza that enters a root cortical cell but stays outside the cytoplasm.

A flask-shaped, jacketed organ that holds the egg and, in bryophytes and ferns, the young embryo.

A stem arrangement of vascular bundles scattered through the ground tissue, usual in monocots.

A simple fleshy fruit whose pericarp is soft throughout, a tomato being the standard example.

A species name formed from a genus and a specific epithet.

The torn neck of the archegonium, haploid gametophyte tissue, that caps a moss capsule and is not part of the capsule wall.

The spore case of a bryophyte sporophyte, where meiosis occurs. In these notes the word is that organ, not a dry fruit.

A megasporophyll folded around the ovules, differentiated into stigma, style, and ovary, which is what the name angiosperm records.

The grain of a grass, a dry fruit whose fruit wall and seed coat have grown into one layer.

The endodermal gasket of a young root, lignin and suberin laid in the walls that face neighbouring cells, so the wall pathway is sealed.

Self-pollination inside a flower that never opens.

Living ground tissue with uneven, usually unlignified primary walls, supporting organs that are still elongating.

The nucleate sister cell of an angiosperm sieve-tube element, which keeps that element alive.

A layer of cutin and waxes secreted onto the aerial epidermis, not itself a cell wall, which limits water loss from the surface.

Fusion of one sperm with the egg and of the second sperm with the central cell, so that a flowering plant forms both an embryo and, in the usual case, triploid endosperm.

A simple fleshy fruit with a stony endocarp around the seed, a cherry being the standard example.

Movement of water over the outer surface of a bryophyte, which is metabolically active when wet and has no lignified vascular column.

A fungal association that sheathes a root tip and sends a Hartig net between cortical cells, without penetrating those cells.

An oil-rich body on a seed that ants carry away and eat, discarding the seed itself.

A spiral-walled cell in a liverwort capsule that helps to scatter the spores.

The female gametophyte of a flowering plant, in the usual *Polygonum* form seven cells and eight nuclei.

A land plant, the clade in which a multicellular embryo is retained and nourished on the parent gametophyte.

Xylem that matures from the inside outward, the usual pattern in a stem.

Nutritive tissue formed after the second fertilisation, triploid when two polar nuclei join one sperm, and not the haploid female gametophyte that feeds a pine embryo.

Growth of the gametophyte inside the spore wall, as in heterosporous lycophytes, water ferns, and seed plants.

A plant that grows on another plant without tapping that plant's xylem.

The angiosperm clade marked by tricolpate pollen, or by pollen derived from that state. Two cotyledons do not define it: a magnolia has two and is not a eudicot, and the old group called dicots is not a clade.

A sporangium that develops from several initials, has a wall more than one cell thick, and holds many spores.

A ring of separate vascular bundles around a pith, the usual primary stem of a eudicot.

Xylem that matures from the outside inward, the usual pattern in a root.

In a gymnosperm, the haploid body that bears archegonia and, in the seed, is itself the food reserve.

The base of a bryophyte sporophyte, which absorbs from the gametophyte to which it stays attached.

A cambial cell that produces the axial cells of secondary xylem and phloem.

The leafy stem of a moss, the persistent photosynthetic body, budded from the protonema.

The haploid generation, which produces gametes by mitosis.

Pollen rejection decided by the pollen grain's own haploid genotype, so a matching tube dies in the style.

Transfer of pollen between flowers of one plant, which is genetically self-pollination even though two flowers are involved.

A multicellular haploid propagule that clones the gametophyte, as in the splash cups of *Marchantia*.

The genetic individual arising from one zygote, which may be composed of many ramets.

One of the paired epidermal cells that bound a stoma, kidney-shaped in most eudicots and dumbbell-shaped in grasses.

The inner wood, with dead parenchyma and conduits often blocked, which is not the main path of water.

A parasite that taps the host's xylem and still carries out ordinary photosynthesis, as mistletoe does.

A collection of pressed, dried, labelled specimens that can be examined again when a name changes.

Production of microspores that become male gametophytes and megaspores that become female ones, a precondition of the seed but not the seed itself.

A floral polymorphism, pin and thrum in *Primula*, that ties stamen height, stigma height, and compatibility together.

A parasite that lacks ordinary photosynthesis and draws its carbon from the host.

The single specimen designated as the type when a name is first published.

Similarity inherited from a common ancestor.

Similarity that arose by convergence or reversal, not from the immediate common ancestor of the groups being compared.

Production of a single kind of spore, the usual condition in bryophytes and in most ferns.

A dead, porous cell of *Sphagnum* that holds water.

A water-conducting cell of some mosses, such as *Polytrichum*, that is not a tracheid.

A cup or tube of fused floral bases surrounding the ovary, as in a perigynous cherry, and not itself the pericarp of that fruit.

The cover of a fern sorus. It does not throw the spores; the drying annulus does that.

An ovary that sits below the other floral parts, so the fruit wall includes tissue from around the ovary as well as the ovary itself.

The sporophyte layer or layers around a nucellus, which become the seed coat.

A leaf bundle sheath rich in chloroplasts and set tight against the mesophyll, the structural form associated with C4 leaves.

A cell or a series of cells that stores latex apart from the ordinary cytoplasm, so the plant does not poison itself with its own metabolites.

The vascular strand that leaves the stem stele and enters a leaf.

A sporangium that develops from a single initial, has a wall one cell thick, and usually bears an annulus.

A vascular plant of the clade that bears microphylls, including clubmosses, spikemosses, and quillworts.

A leaf with branching veins, typical of ferns and seed plants, defined by that vascular pattern and not by being large.

A leaf with a single vein and no associated leaf gap, the lycophyte leaf, defined by that pattern and not by being small.

The opening left by the integuments, through which a pollination drop or a pollen tube approaches the nucellus.

The pectin-rich layer, shared by two cells, that cements their walls together.

A member of the fern clade in the broad sense, including leptosporangiate and eusporangiate ferns and the horsetails. *Psilotum* belongs here as a reduced fern, not as a model of the earliest vascular plants.

The status of a group that contains an ancestor and all of its descendants.

The megasporangium of an ovule, inside the integuments.

A nucellus plus integuments, with a micropyle, which is a seed only after an embryo has been formed. It is not a gamete.

The woody scale of a pine cone, borne in the axil of a bract, with ovules on its upper surface. The cone is a compound shoot, not a simple stack of sporophylls.

The columnar mesophyll, usually on the adaxial side of a dorsiventral leaf.

The status of a group that includes an ancestor but leaves out some descendants, which is the status of the old "dicots".

The outer layer of the root stele, from which lateral roots arise and push out through the cortex.

The secondary skin of cork, cork cambium, and phelloderm that replaces an epidermis split by growth in girth.

The ring of hygroscopic teeth around the mouth of many moss capsules, which moves with humidity and meters spore release.

A secondary metabolite from the phenylpropanoid pathway, the class that includes anthocyanins, flavonols, tannins, and lignin.

A microspore that has already begun the male gametophyte. It is not a sperm; the sperm are produced later by mitosis.

Movement of pollen onto a stigma, or, in a gymnosperm, onto an ovule. It is not fertilisation, which is the later fusion of gametes.

A secreted drop at a gymnosperm micropyle that catches airborne pollen and, on withdrawal, draws it to the nucellus.

The status of a group assembled from convergent members and excluding the ancestor that would unite them.

A sharp outgrowth of the epidermis or cortex with no vascular trace connecting it to a stele, as on a rose.

An extinct plant that made woody secondary xylem and bore fern-like fronds, and that was neither a fern nor a living conifer.

Maturation of the stamens before the carpels of the same flower, so that male and female function are separated in time.

The small, free-living gametophyte of a homosporous fern, which still needs a film of water before its sperm can swim.

The filament that grows from a moss spore and from which leafy gametophores bud.

Apomixis in which the egg develops without being fertilised, while the endosperm still requires a fusion with a sperm.

An extinct seed plant with fern-like leaves. It is a seed plant, not a fern.

A group of slowly dividing cells among the root-tip initials, able to replace initials that are damaged.

A shoot or other module that can live physiologically on its own, one part of a genet.

A cambial cell that produces the rays rather than the axial wood and phloem.

An anchoring filament of a bryophyte or of a fern gametophyte, lacking a root cap, a stele, and root hairs, and therefore not a root.

A stem that grows horizontally, bearing scale leaves, and that may store as well as spread.

The dead outer bark built up outside successive cork cambia.

The outer wood, whose conduits still conduct water.

Ground tissue with a thick, usually lignified secondary wall, often dead at maturity, supporting organs that have stopped growing.

The wall layer laid down inside the primary wall after a cell has stopped expanding, thick and usually lignified in tracheary elements and fibres.

The living seeds buried in soil, which can outlast the plants growing above them and which are not a stored packet on a shelf.

The stalk of a bryophyte sporophyte. In a moss it lengthens before the capsule is ripe; in a typical liverwort it lengthens only after the capsule has matured.

An angiosperm phloem cell that meets its neighbours at sieve plates, keeps a plasma membrane, and has no working nucleus when mature.

Delivery of non-motile sperm through a pollen tube, as in conifers and flowering plants. In cycads and *Ginkgo* the sperm still have flagella, yet the swimming is confined to the interior of the ovule.

A cluster of fern sporangia, commonly on the lower surface of a frond.

A leaf, or part of a leaf, modified as a sharp defence, and therefore occupying a leaf position.

The diploid generation, developed from the zygote, which produces spores by meiosis.

Pollen rejection decided by the diploid parent's genotype, the determinants carried in the pollen coat from the tapetum, so a matching grain is stopped at the stigma.

The resistant polymer in the wall of a spore, and of the outer wall of a pollen grain, that lets those cells survive in air.

The thin place in a leptosporangium wall where the drying annulus tears it open.

The clade made up of the charophyte green algae plus the land plants, as distinct from the chlorophyte green algae.

Directional change in vegetation after a disturbance, primary where soil and a seed bank are absent and secondary where they remain. It is not the development of one climax organism, and a grassland held by fire is not a failed forest.

An ovary attached above the other floral whorls.

The living cytoplasms of a plant body joined through plasmodesmata.

A shared derived character, the kind of similarity used as evidence that a group is a clade.

One of the two cells beside the egg at the micropylar end of the embryo sac, involved in receiving the pollen tube.

A phenolic that binds protein, which discourages feeding and also slows the decay of litter.

The sporophytic lining of the anther, which feeds the developing grains and deposits the coat used in sporophytic self-incompatibility.

The wild grass from which maize was domesticated, in particular Balsas teosinte of southern Mexico: a branched plant with terminal tassels and small ears that shatter, the grains held in hard cupules.

A secondary metabolite assembled from five-carbon isoprene units, a biosynthetic class that does not share one ecological job.

A sharp stem in the position of an axillary branch.

The thickened centre of the pit membrane between conifer tracheids, which can block the pit if one tracheid fills with air.

A dead, lignified water-conducting cell, present in every vascular plant, that passes water only through pits.

Of pollen, having three grooves, the usual condition in the eudicots and the shared derived character of that clade.

A swollen stem that stores, recognised by buds, or eyes, rather than by the fact that it holds starch.

The specimen to which a scientific name is tied, whether a holotype, a later lectotype, or a neotype, and not the individual that looks most typical.

A dead water-conducting cell, usually wider than a tracheid, stacked into a vessel and open through perforation plates. Vessels are typical of angiosperms but are not a character of one clade: they are missing in some early lineages and evolved more than once.

The streptophyte algal class, including *Spirogyra* and the desmids, that current phylogenies generally place as the closest living relatives of the land plants. They conjugate, and they lack both flagella and archegonia, so the sister group of embryophytes need not look like a moss.