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Plants |
| PLANTS | Glossary D-K |
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Pieces |
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Plants |
| PLANTS | Glossary D-K |
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Unit Cladogram |
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Pieces |
Deciduous: falling off; in plants: shedding leaves annually.
Dehiscence: any process used to expel spores, microgametes, or seeds into the environment. To be more precise, dehisence refers to the steps which the plant performs to expose the seeds, etc. to the environment. Dispersal is the mechanism by which they are actually distributed in the environment. So, for example, moss spores may dehisce by the opening of the operculum and retraction of the peristomal teeth. They are then dispersed by wind. However some plants, like Sphagnum moss, may explosively dehisce and so get involved in dispersal as well.
Dichotomous branching: a type of branching in which the tip divides into two more-or-less equal apices; by repetition of this type of branching in various planes distinctive shoot systems may be produced.
Dioecious: used to describe plant species in which male and female sex organs are borne on separate individuals.
Diploid: a nucleus is diploid if it contains two copies of each non-redundant gene. In Fungi, it is necessary to distinguish between diploid nuclei and diploid cells. A hypha may contain several haploid nuclei (either identical or from different individuals). Technically, the cell is diploid or polyploid. However, there may be no diploid nuclei.
Diplolepidous:
of moss sporophytes, having an inner (endostome) and outer (exostome) row of
plates forming the peristome
teeth. See Tree
of Life: Bryopsida.
Diplolepidous-opposite: of moss sporophytes, having an inner (endostome) and outer (exostome) row of plates forming the peristome teeth as radial elements between them. See Tree of Life: Bryopsida.
Dispersal: to disperse: to dispel or scatter; in plants dispersal refers to mechanism of dispersing reproductive propagules like seeds or pollen.
Double fertilization: in flowering plants: the more or less simultaneous union of one sperm and one egg to form a zygote (N=2) and another sperm with two polar nuclei to form triploid (N=3) endosperm in the ovule; in the Gnetales: the fusion of two sperm with two eggs to produce two zygotes, only one of which will mature into an embryo.
Double integument: the two outermost layers of an ovule in angiosperms, one of which will differentiate into the seed coat; see integument.
Embryophyte: the group of all organisms that retain the zygote on the parent to form an embryo, includes Bryophyta and vascular plants.
Enation: a non-vascularized, epidermal outgrowth
found in some early land plants.
Endosperm: the triploid (N=3) product of double fertilization in angiosperms; during seed maturation the endosperm will develop into a storage tissue that will provide nutrients to the seedling as it emerges (in monocots) or that will be digested and stored by the cotyledons before germination (in dicots)
Endospory: a condition in which the gametophyte develops within the spore wall, rather than externally.
Endostome: of moss sporophytes, the inner row of walls forming the peristome teeth. See Tree of Life: Bryopsida.
Endothecium: the inner cell mass of the sporpphyte in basal plants. It usually produces both the central columella and the spores, which accumulate around the surface of the columella.
Entire margin: in leaves, the condition in which the margin forms a smooth line or arc without noticeable serrations; note that lobed leaves can also have entire margins; compare to lobed margin and toothed margin.
Epidermis: the exterior tissue, usually on cell thick, of leaves and young stems and roots.
Epigonium: in mosses, a derivative of the archegonium which forms a hard, protective layer around the developing sporophyte. Later it breaks up, but the sporophyte retains a conical "dunce cap" or calyptra over its distal end. Strictly speaking, the term calyptra refers only to the "dunce cap," and the piece of the epigonium retained around the base (if any) is the vaginula.
Epiphyte: a plant that grows on another plant, or which uses a rock or host plant merely as a place of residence and obtains its moisture and nutrients directly from the air; an air plant. A type of growth form. No parasitism is involved. The epiphyte is rooted on the surface of the host. Vines rooted in the soil and climbing up on another plant are not epiphytes.
Eusporangium: sporangia that arise from a group of superficial cells; this is the primitive character state in vascular plants; compare to leptosporangium.
Evergreen: opposite of deciduous, i.e. evergreen plants do not shed all their leaves annually, but shed and grow new leaves continually; most conifers are evergreen, but the evergreen habit is not restricted to conifers.
Exostome: of moss sporophytes, the outer wall
of plates forming the peristome
teeth. See Tree
of Life: Bryopsida.
Fiber cell: a long-walled plant cell which is often dead at maturity; fibers impart elasticity, flexibility and tensile strength to plant structure
Fission: cytoplasmic division of a cell to form two cells, a form of asexual reproduction.
Flagellum:
(pl. flagella) A eukaryotic flagellum is a bundle of nine fused pairs of microtubules
called "doublets" surrounding two central single microtubules (the
so-called 9+1 structure of paired microtubules; also called the "axoneme"). At the base of a
eukaryotic flagellum is a microtubule organizing center about 500 nm long,
called the basal body or kinetosome. The flagellum is
encased within the cell's plasma membrane, so that the interior of the flagellum
is accessible to the cell's cytoplasm. This is necessary because the flagellum's
flexing is driven by the protein dynein bridging the microtubules all along its
length and forcing them to slide relative to each other, and ATP must be
transported to them for them to function. This extension of the cytoplasm is
called the axosome. Important note: The eukaryotic
flagellum is completely different from the prokaryote flagellum in structure and
in evolutionary origin. The only thing that the bacterial, archaean, and
eukaryotic flagella have in common is that they stick outside of the cell and
wiggle to produce propulsion. From Flagellum - Wikipedia. Image:
O'Kelly et al. (1999).
Flower: condensed reproductive shoot of
flowering plants, generally consisting of four whorls from the outside in: sepal,
petal, stamen, and
carpel; the diversity of flower form comes from
variation of the general four-whorled structure. Image from the Great
Plant Escape site of the University of Illinois.
Forb: a small, upright soft-stemmed or non-woody plant with broadleaves; the growth form of many common wildflowers.
Frond: leaf of a fern
Fusiform: tapering towards each end; football-shaped
Gametangium: the sexual organ of the gametophyte generation -- either an antheridium ("male")or archegonium ("female").
Gametophore: the structure on the gametophyte which actually produces the gamete. Note that this distinction between gemetophyte and gametophore is usually only necessary in the liverworts and mosses, in which the gametophyte generation is dominant and the gametophyte includes all the basic structures for vegetative growth.
Gametophyte: the haploid phase (n=1) of a life cycle on which gametes (reproductive cells) are produced.
Gemma:
(pl. gemmae) a bud (or simply a group of cells) from which plants
vegetatively reproduce.
Growth form: the overall morphology of a plant species, including its stature, leaf type, and habit. The general description of the type of growth exhibited by a plant, such as herbaceous, shrubby (bush-like) and arborescent (tree-like). The most basic grow forms are trees, shrubs, forbs, and graminoids; but there are many more specialized growth forms such as epiphytes, lianas, and stem succulents.
Haploid: a nucleus is haploid if it contains only one copy of each non-redundant gene. The great majority of animals, and higher plants, are diploid. That is, the form we usually observe has two copies of each gene, one from each parent. In lower plants there are numerous exceptions to the rule. Furthermore, the gametophyte generation (see alternation of generations) is always haploid.
Herb: any non-woody vascular plant; a category of plants including both forbs and graminoids (grasses). Hence the term "herbaceous" layer. Herbaceous: having this sort of growth form.
Heterogametes: male and female gametes that are morphologically distinguishable.
Heterosporous: having two types of spores: megaspores and microspores.
Heterospory:
a condition in which an organism produces two different types and sizes of spores, viz.
microspores and megaspores. As a reproductive strategy,
heterospory involves the following steps: (1) The mature diploid plant (sporophyte)
produces "male" and "female" spores. Typically,
the plant produces numerous small "male" spores (microspores)
and fewer, but larger "female" spores (megaspores). (2)
The megaspores are usually retained on the sporophyte, where a haploid female gametophyte
develops inside the spore. (3) The microspores may or may not be retained
on the sporophyte. They develop into sperm-producing, haploid
gametophytes. (4) The sperm are released into the environment, and
dispersed between plants. (5) The sperm fertilize female gametophytes
grown from megaspores, producing a diploid zygote (fertilized
cell). (6) The zygote develops into an embryo and finally a new diploid
sporophyte. Heterospory evolved a number of times among different ancient
plants. Lycopsids, ferns, sphenopsids and progymnosperms all developed
heterospory. Many of these plants also evolved into large trees. The
obvious advantage for heterosporous trees is that their great height would
enhance the dispersal of windborne microspores. Competition for light in the
shady Archaeopteris forests, may have also have encouraged heterospory,
since the macrospores, like seeds, included food reserves to assist early plant
growth. Heterospory is generally regarded as the precursor to the
evolution of seeds. Microspore dispersal and macrospore viability in
pteridosperms thus become pollen dispersal and ovule viability in seed-bearing
plants. The change in sexual reproduction from moisture-bound gametophytes
to seeds-bearing sporophytes enable vascular plants to colonize drier habitats
and upland environments, and also provided the embryo with a protective case
against hungry invertebrate herbivores.
Heterotrichous: (filament) a growth pattern of algae with prostrate filaments for attachment and erect, spreading filaments for photosynthesis.
Holdfast: algal organ for attachment.
Homosporous: having one type of spore.
Homospory: a condition in which an organism produces only one type and size of spores, (microspores).
Hydroid:
The water storage or water vascular cells of Bryophyta.
Analogous to xylem in
tracheophytes.
Integument: the outermost layer(s) of an ovule which will develop into the seed coat; most seed plant ovules have one integument, angiosperm ovules have two integuments (see double integument).
Intercalary meristem: see meristem.
Karyogamy: fusion of two (haploid) nuclei.
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