Virtual Paleobotany Laboratory
GLOSSARY
abaxial on the lower
surface; situated or directed away from an axis
adaxial on the upper
surface; situated or directed toward an axis
actinostelea type of protostele that looks like a star in cross section
allochtonoussomething that
has been transported
amphiphloichaving phloem on both sides of the xylem
analogous, analogy opposite
to homologous: correspondence in function between
anatomical parts of different structure and origin; analogous: exhibit
analogy (synonym: similar)
annulusspecialized of some
fern sporangia that are involved in the opening
of the sporangium: on drying out the cells of the annulus contract and the
sporangium ruptures, releasing the spores
antheridiareproductive
structure that produces male gametes (sperm)
anthracitesee coal
apical meristem
embryonic, totipotent tissue in the tips of the roots and shoots of plants
apomorphysame as derived trait
archegoniareproductive structure
that produces female gametes (egg)
ataxonomican approach in
which interpretations are not based on taxonomic assignment; for example:
if a fossil taxon has the same generic name as an extant taxon,
interpretations about the ecology of the fossil taxon are not based on the
ecology of the extant taxon
autapomorphyderived trait or apomorphy that is
unique to only one group or OTU
autochtonoussomething that
has not been transported
axissee stem
basal taxon / groupa group
near the root of a clade
bifacial (vascular
cambium)having two "faces", i.e. a vascular cambium that produces cells on both
sides; in seed plants phloem is produced to the
outside and xylem to the inside; compare to unifacial (vascular cambium); see cambium
biocoenosislife
assemblage; an assemblage of fossils that reflects associations
characteristic of the community when it was living
bisaccatea pollen grain
with two sacci
biseriatein two ranks or
rows in the same plane
bituminous coalsee coal
cambiuma lateral meristem that produces secondary growth
carbonatea salt or ester
of carbonic acid (H2CO3); carbonates can combine with other elements to
form minerals, for example with calcium (calcium carbonate) or with iron (iron carbonate)carinal canala ca
nal in the xylem of some sphenophytes, for
example Equisetum, that results from extension and rupture of the protoxylem elements
carpelthe female reproductive
organ of a flower, consisting of stigma, style and ovary
castopposite of mold; a preservation type that forms within a mold;
casts are usually three-dimensional and therefore preserve form
cellulosepolysaccharide
that consists of a long unbrached chain of glucose units; cellulose is the
main constituent of the cell walls of most land plants
characterheritable trait
possessed by an organism; characters are usually described in terms of
their states, for example: blue and red as character
states for the character flower color
character reversalcharacter
that reverses to a more ancestral state
character statethe state
or value of a character; for example some character states for the
character 'color' are red, green and blue
cherta type of rock; chert can
form as a primary deposit preserving fossils within it, or replace organic
materials in fossils embedded in different rock material
cladea group of organisms that
share a common ancestor; lineage; a monophyletic group
cladisticssame as phylogenetic systematics
cladograma dichotomous
phylogenetic tree that branches repeatedly, suggesting a classification of
organisms based on the sequence in which evolutionary branches arise; a
nested diagram of synapormorphies indicating
relations between groups; each point of branching represents divergence
from a common ancestor
coala general name given to
stratified accumulations of carbon-rich material derived from vegetation.
The starting point for coal formation is ususally peat or some similar
accumulation of partially decayed plant matter. By the process of
compaction, heating, and chemical alteration, the peat is converted by a
series of stages into coal. The type of coalification corresponds to the
amount of heating that a peat has undergone:
- Peat
- Lignite (brown coal)
- Bituminous coal
- Anthracite
coal ballsa type of
preservation known from Carboniferous and Permian coal seams, in which
plants are preserved by calcium carbonate and
other minerals; see petrifaction and permineralization.
collenchymatissue
composed of unevenly thickened cell walls; collenchyma cells are flexible
and support young parts of the plant without hindering growth; collenchyma
cells are composed of cellulose
compactionin
sedimentation: the formation of massive rock from loose sediment, normally
brought about by the weight of the overlying sediments; in preservation:
organic preservation in three dimensions, for example in peat or clay
companion cella
specialized cell of phloem, derived from the
same parent cell as the closely associated sieve-tube
element immediately adjacent to it; the nucleus of the companion cell
supports both its own cell andthe cell of its associated the sieve-tube
element
complex tissuetissue that
consists of more than one cell type, e.g. phloem
compressiona fossil
preservation type in which a thin film of organic matter is preserved;
compare to impression
conesee strobilus
convergent evolution,
convergence the independent development of similar
(analogous) structures in different groups;
convergent evolution is thought to be the result of similar environmental
selection pressures on different groups
corka plant tissue composed of
cells whose walls are impregnated with suberin and are non-living at
maturity; cork is produced by the cork cambium
cork cambiuma narrow
cylindrical sheath of meristematic cells that
produces cork cells to replace the epidermis during secondary growth (growth in width)
cortexa primary tissue
composed mainly of parenchyma cells, which
extends between the epidermis and the vascular tissue
cotyledonthe embryo leaf
or leaves of seed plants that usually stores or absorbs food in a young
seedling; in angiosperms (flowering plants) the following distinction is
made with respect to the cotyledons: dicots have two
cotyledons and monocots have one cotyledon
cross-section see transverse section
crozierthe spirally coiled
"fiddlehead" of an immature fern leaf
cupulestructures that
surround one or more ovules or seeds; the cupule lobes may be free or united
cuticlean impermeable layer
of cutin on the outer walls of epidermal cells
cutinthe waxy substance of
which a cuticle is composed
deciduousfalling off; in
plants: shedding leaves annually
decussate branchinga type
of branching in which the appendages are attached in pairs either
alternately (alternate decussate) or at right angles (opposite decussate)
to one another; the result are four ranks or rows of appendages
derived traitsame as
apomorphy; a derived character / trait is inferred to be a
modified version of a more primitive condition of that character and
therefore inferred to have arisen later in the evolution of the clade
determinate growtha type
of growth in which the axis ceases growing, usually after the apical meristem differentiates into a reproductive
organ, such as a flower or a cone
dichotomous branchinga
type of branching in which the apical meristem
divides into two more-or-less equal apices; by repetition of this type of
branching in various planes distinctive shoot systems may be produced; for
example see decussate branching
dictyostelea dissected
siphonostele with two or more overlapping leaf
bases
dioecioushaving unisexual
reproductive structures confined to separate plants, i.e. female
plants have only female reproductive structures, and male plants will have
only male reproductive structures; compare with monoecious
disjunct
distributiondiscontinuous distribution of a species
disparitydistinct in
morphological characters; morphological variation; compare to diversity
dispersalto disperse: to
dispel or scatter; in plants dispersal refers to mechanism of dispersing
reproductive propagules like seeds or pollen
diversitya terms used to
describe number of taxa (species, genera etc.) and their relative
abundance; also species richness; compare to disparity
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
integumentthe two outermost layers of an ovule in angiosperms, one of which will differentiate
into the seed coat; see integument
ectophloichaving phloem only on the outer side of the stele;
compare to amphiophloic
embryophytethe group of
all organisms that retain the zygote on the parent to form an embryo
enationa non-vascularized,
epidermal outgrowth found in some early land plants
endarcha type of xylem maturation in which protoxylem is internal to metaxylem and development prodeeds centrifugally
(from the inside out); for comparison see exarch and
mesarch
endemicbelonging or native
to a particular region or area and found only in that area, for example a
plant endemic to California is native to California, i.e. in the wild it
occurs only in California
endospermthe 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)
endosporicgametophyte develops within the spores wall;
compare with exosporic
endotestathe delicate,
innermost layer of the integument in some seeds; compare to sarcotesta
and sclerotesta
entire margin
(leaves)margin forming a smooth line or arc without
noticeable serrations; note that lobed leaves can also have entire margins;
compare to lobed margin and toothed margin
epidermisthe exterior
tissue, usually on cell thick, of leaves and young stems and roots
Euphyllophytinaclade comprising the seed plants, sphenopsids, ferns and Ps
ilophyton; synapomorphies for the clade include among others a
basically helical arrangement of small, pinnule-like vegetative branches,
recurvation of branch apices and paired sporangia grouped into terminal
branches
eusporangium,
eusporangiateeusporangium: sporangium that arise from a
group of superficial cells; this is the primitive character state in vascular plants; compare to leptosporangium
eustelea stele type, in which the vascular bundles are organized
into strands of xylem flanked by strands of phloem on the outside; in transverse section the eustele appears as a ring of
discrete vascular bundles;
evergreenopposite 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 evergreeen habit is not restricted to
conifers
evolutionary gradesame as
paraphyletic groupshowing similarities in morphology,
ecology or life history
evolutionary
systematicssame as synthetic systematics; a way to
determine natural relationships of organisms by studying a group in detail
and comparing degree of similarity; evolutionary systematics does not have
an explicit methodology, but rather relys on the expertise of authorities
very familiar with the group in question; compare to phenetics or numerical
taxonomy and phylogenetic systematics or cladistics
exarch a type of xylem maturation in which protoxylem is external to metaxylem and development prodeeds centripetally
(from the outside in); for comparison see endarch
and mesarch
exinethe outermost layer of
the wall of pollen and spores;
made of sporopollenin; compare to intine
exosporicgametophyte development outside the spore wall, i.e. the development of a free-living,
multicellular gametophyte
extantcurrently existing;
living now
extinctno longer existing;
not living anymore
fibera long-walled plant cell
which is often dead at maturity; fibers impart elasticity, flexiblility and
tensile strength to plant structure
flowercondensed 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
form taxonbinomial name
(genus and species) given to a fossilized plant organ when it is found in
isolation, i.e. when the taxonomic affinities of the organ are not known
with certainty; for example spore and pollen taxa have their own binomial names, since it is
rarley known which fossil genus may have produced them
fossilany evidence of past
life; any remains of any once living organism preserved in the Earth's
rocks
frondleaf
of a fern
fusainfossil charcoal; a
component of coal and sedimentary rocks characterized by black color, silky
luster and fibrous texture
fusiformtapering towards
each end; football-shaped
gametophytethe haploid
phase (n=1) of a life cycle on which gametes are produced
gradesee evolutionary grade
ground tissuea tissue
consisting mostly of parenchyma cells that makes
up the bulk of a young plant
growth formgeneral
description of the type of growth exhibited by a plant, such as herbaceous,
shrubby (bush-like) and arborescent (tree-like)
heterochronyan
evolutionary change in phenotype based on an alteration in timing of
developmental events
heterosporoushaving
two types of spores: megaspores and microspores
homologous,
homologyhomology: likeness and correspondence in
structure between parts of different organisms, due to common ancestry of
the organisms; compare to analogy;
homoplasysame as convergence;
homosporoushaving one
type of spore
hydroidthe water conducting
cells of bryophytes; compare to leptoid
impressiona type of
preservation that represents the negative imprint of an organism; compare
to compression
index fossila
geographically widespread fossil, that is diagnostic of a particular time
period and therefore useful in correlating the age of rock formations from
different geographic areas
integumentthe outermost
layer(s) of an ovule which will develop into the seed
coat; most seed plantovules have one integument,
angiosperm ovules have two integuments (see double integument)
internodethe segment of a
plant stem between the points where leaves are attached
intinethe innermost layer of
the wall of pollen and spores;
made of cellulose and pectates; compare to exine
leafa flattened, photosynthetic
structure of a plant arranged on a stem
leaf gapa parenchyma filled
interruption in a stemís cylinder of vascular tissue immediately above the
point at which a branch of vascular tissue
(leaf trace) leading to a leaf occurs
leaf tracea branch of
vascular tissue leading from the main vascular cylinder of the stem to a leaf
leptoidphotosynthate
conducting cells of bryophytes; compare to hydroid
leptosporangium,
leptosporangiateleptosporangium: sporangium developed from
a single superficial cell; leptosporangiate: having leptosporangia; this is
a derived character state in the fern clade;
compare to eusporangium
lignitesee coal
ligulea tiny, tongue-like
appendage on the adaxial surface of leaves of some
members of the lycopods
lobed margin
(leaves)margin indented one quarter or more of the
distance from the margin to the midvein or (where this is lacking) to the
long axis of the leaf; compare entire margin
and toothed margin leaves
long shootshoots that are
distinguished by their widely separated nodes and and internodes; compare
with short shoot
lumenintercellular space
manoxylic woodwood type
that contains abundant parenchyma; typical of
cycads; compare with pycnoxylic
massulea large mass of
mucilagenous material that encloses the microspores of water ferns like
Azolla
megagametophytein heterosporous plants and in seed plants: the female gametophyte produced by a megaspore
megaphylla
leaf with more than on vein and a leaf
trace associated with a leaf gap in the stele;
compare to microphyll
megasporangiuma sporangium that produces megaspores; see also heterosporous
megasporea large, haploid
(N=1) spore of a heterosporous plant that
produes a megagmetophtye (female gametophyte)
meioticpertaining to
meiosis: a two stage type of cell division in sexually reproducing
organisms that produces gametes with half the chromosome number of the
original cell
meristemregion of
totipotent cells in which cell division and initiation of tissues and
organs takes place; see apical meristem, vascular cambium and cork
cambium
mesarch a type of xylem maturation in which the protoxylem is embedded in the metaxylem and development proceeds both centripetally
(from the outside in) and centrifugally (from the inside out); compare to
endarch and exarch
mesophyllparenchyma tissue between the upper and lower epidermis of a leaf
metaxylema type of primary
xylem that differentiates and matures later than
the protoxylem; generally metaxylem tracheids are
longer than protoxylem
microgametophyte in
heterosporous plants and in seed plants: the male gametophyte produced by a microspore
microphylla
leaf vascularized by a single vascular bundle that is not associated with a leaf gap in the stele; this type
of leaf is typical of the lycopods; compare to megaphyll
micropylea small opening
in the integument at the apex of a seed through which either pollen (gymnosperms) or the
pollentube (angiosperms) enters
microsporangiuma
sporangium that produces microspores; also see heterosporous
microsporea small,
haploid (N=1) spore of a heterosporous plant
that produces a microgametophyte (male
gametophyte)
midden, pack-rat
middenmidden: garbage or refuse heap; packrats
(Neotoma sp.) collect and store plant and animal parts in middens;
plant material is preserved and cemented together by urin and feces from
the packrats; packrat middens are only found from the later part of the
Pleistocene through the present, but their fossils have been instrumental
in reconstructing Pleistocene and Holocene vegetational changes in the
North American southwest and have also been important in archeological
studies
molda three-dimensional
preservation type that represents a negative image of the plant; compare to
cast
molecular
fossilnon-structural compounds, for example break-down
products of pigments or lignins
monocarpica plant that
produces reproductive propagules only once in its lifetime
monoecious having female
and male reproductive structures on the same plant; the reproductive
structures can be either unisexual or bisexual; compare to dioecious
monophyly, monophyletic
groupterms applied to a group of organisms that include an
ancestor and all of its descendants; compare to paraphyly, paraphyletic groups and polyphyly, and polyphyletic groups
monosaccate a pollen
grain with one saccusor buoyant bladder
monostelichaving one stele; compare to polystelic
morphometricsmethod to
define and describe morphological characters and character states based on
quantifiable measurements; morphometrics can also help define form taxa by
evaluating ranges of variation within and between groups
node1. region of a stem where
one or more leaves are attached; compare to
internode; 2. the branching points on a cladogram, which are supported by synapomorphies
nucellusovule tissue within which an embryo develops (embryo
sac); homologous with the megasporangium of a
seed plant
numerical taxonomysame as
phenetics; a method of generating phylogenies
that is based on large numbers of quantifiable (measureable) characters which groups organisms with respect to overall similarity
ontogenythe course of
development of an individual organism
Operational Taxonomic
Unitsee OTU
orderor evolutionary order;
which character state that must follow another in a character
transformation series - without any implication as to what characters are
primitive versus derived. For example, the order of the character states
"grey", "white", and "black" could be hypothesized to be white-grey-black
(or black-grey-white).
OTUor Operational
Taxonomic Unit; definitions or names of the taxa included in a
phylogenetic analysis
overall similaritya method
by which organisms that share the most similarities are grouped together;
characters are not distinguished as to whether
they are primitive or derived or whether they are evolutionary meaningful;
also see numerical taxonomy (phenetics); compare
with phylogenetic systematics (cladistics)
ovarythe enlarged basal
portion of a carpel, where the ovules are borne; the ovary differentiates into the fruit
ovuleunfertilized seed; the ovule contains the megasporangium with the megagametophyte, surrounded by one or two
integuments integument
palynomorphfossil spores
and pollen; also dinoflagellates
parallell evolutionsee
convergent evolution
paraphyly, paraphyletic group
terms applied to a group of organisms that include an ancestor and some,
but not all of its descendants; compare to monophyly,
monophyletic groups and polyphyly, and polyphyletic groups
parenchymathe most common
type of plant cell; thin-walled cells varying in size, shape, and function
parichnosan interconnected
system of parenchymatous strands with many air spaces that extend
throughout the vegetative organs of some arborescent lycopsids
parichnos scarssmall scars
that marks the position of the parichnos strands
on stem fossils of the some arborescent lycopsids
peatsee coalaccumulations of terrestrial organic material with
little associated mineral sediment
periderma tissue primarily
consisting of cork cells; outer bark
permineralizationa
preservation type in which mineral matter has infilled intercellular and
intracellular spaces, but has not replaced the cell walls; compare
to petrifaction and silification
petalone of the whorls
of a flower; petals may be brightly colored
petiolethe stalk of a leaf
petrifactiona type of
preservation in which mineral matter infills intercellular spaces and
replaces the cell walls; compare to permineralization and silification
phenetics, phenetic
systematicssame as numerical
taxonomy
phenetic similaritysame as
overall similarity
phloemphotosynthate
conducting tissue of vasular plants
phosphatePO34-; a
mineral that often participates in permineralization
phylogenetic
charactersee character
phylogenetic
systematicssame as cladistics; a
method of grouping organisms that is basedsynapomorphies or shared derived traits or characters; compare to numerical taxonomy
phylogenyan hypothesis of
evolutionary relationships among organisms; the pattern of lineage
branching produced by the evolutionary history of the organisms considered
physiognomy, foliar
physiogonomyanalysis of leaf features that are sensitive
to environment
pinnaeplural: (primary) pinna;
first order of subdivision of a compound leaf or fern
frond
pinnulethe second order of
segments of a compound or dissected leaf leaf or
frond
piththe central parenchymatous
tissue in a vascular plant axis
platyspermica flattened
seed with bilateral symmetry
plesiomorphy, plesiomorphic
traitsame as primitive trait
polaritydirection of
evolutionary change; evolutionary order, i.e which character state follows another in a character
transformation series
pollenthe microspore of seed plants that contains the microgametophyte (male
gametophyte)
pollinationthe transfer
of pollen from the pollen organ to the ovule; for
example in flowering plants fromstamens to the
stigmatic surface of the carpel
polyphyly, polyphyletic groupa
group of organisms with different most recent ancestors
polystelichaving more
than one stele
primary growthgrowth in
length, controlled by the apical meristem
primary pinnaeleaflet of
first subdivsion of a fern frond or compound leaf
primitive traitsame as
plesiomorphy; a character that is present in the common
ancestor of a clade; a primitive trait is inferred to be the original
character state of that character within the clade under consideration;
compare to derived trait
procambiumthe primary meristematic tissue that gives rise to primary xylem and primary phloem;
procambia are found in apical as well as intercalary meristems
protostele a type of
stele with a solid core of primary xylem
protoxylemthe first
primary xylem to differentiate and mature,
usually before and during elongation of the axis; protoxylem cells are
generally smaller in diameter than metaxylem
pychnoxylic wooddense
wood that contains little parenchyma; typical of Archeopteris
conifers; compare to manoxylic
pyriteFeS2 a
common mineral that participates in permineralization
quadriseriatein four
ranks or rows; for example see branching
radiospermica round seed; a seed with radial symmetry
rhizomea (usually)
underground stem that is horizontally oriented; rhizomes may appear like
roots, but have a definite node and internode architecture
roota plant organ that
functions in anchorage and absorption; in seed plants derived from a
bipolar embryo
saccate pollenpollen with a
saccus or sacci;
characteristic of many conifers
saccus/saccia winglike or
bladderlike extension on a pollen grain;
sarcotestathe usually
parenchymatous outer layer of the integument in
some seeds; see also endotesta and sclerotesta
sclereida short, irregular
sclerenchyma cell with pits; sclereids function
as tissue support
sclerenchymatissue
composed of cells with walls thickened with lignin; sclerenchyma tissue
functions primarily in strengthening and support
sclerotestathe middle,
fibrous layer of the integument in some seeds; see endotesta and sclerotesta
secondary growthgrowth
in width initiated and maintained by the vascular
cambium and cork cambium
secondary xylemxylem
produced by the vascular cambium, see also xylem, and compare with primary
and secondary growth
seed plantsa monophyletic
clade of plants that reproduces by seeds;
megagametophyte is retained on the parent sporophyte and enclosed in an
integument; microgametophyte is transferred to the megagmetophyte
seeda fertilized ovule; megasporangium that
contains an embryo enclosed in an integument
segmentindividual divisions
on a pinnule
sepala whorl of a flower; sepals often resemble reduced leaves and
function in the protection of the bud; sepals may be modified to function
more like a petal
short shootshoots that
are characterized by short internodes giving the shoot a crowded
appearance; compare with long shoot
sieve cella phloem conducting cell type in all vascular plants
except angiosperms
sieve platearea of the wall
of a sieve tube element that contains several to many perforations that
permit cytoplasmic connections between sieve tube
cells
sieve tube cell(in
angiosperms) a specialized cell derived from the same parent cell as the
closely associated companion cell immediately
adjacent to it; sieve tube cells are elongated cells with sieve plates;
sieve tube cells form sieve tubes through which photosynthate is transported
silificationa type of
fossilization in which silica (SiO2) infills intercellular
spaces (permineralization) or replaces the cell
walls (petrifaction )
silicaSiO2;
ocurring in crystalline (quartz), cryptocrystalline (very finely
crystalline; crystals are very, very small) (opal) and non-crystalline
(chert) forms; one of the most common minerals in the crust of the earth;
an important mineral in the process of silification; also see
permineralization
simple tissuetissue
composed of only one cell type
siphonostelea type of
stele that consists of a ring of vascular tissue surrounding a pith
sinusthe indentations of a
lobed pinna / segment of a fern
or of a dicot leaf
sister grouptwo clades that
resulted from the splitting of a single lineage; sister groups share a
common ancestor
sorus, sori a cluster or group
of sporangia; most frequently applied to
clusters of fern sporangia
sporangiophorethe
stalk which terminates in a sporangium is produced
sporangium,
sporangiastructure in which spores
are produced
sporea haploid (1N)
reproductive cell capable of developing directly into a gametophyte without uniting with another cell
sporophylla modified leaf
bearing sporangia
sporophytethe spore producing, diploid (2N) phase of the life cycle;
compare to gametophyte
sporopolleninan
organic polymer that makes up the coat of a pollen grain or spore;
sporopollenin is extremely resistant to degradation
stelethe central vascular
cylinder in stems and roots where the vascular
tissue is located
stemsame as
axis; a plant axis with leaves or enations
stoma, stomataa minute prore
or opening in the epidermis of leaves; stomata are flanked by two guard
cells that regulate opening and closing of the pore and thus regulate gas
exchange and transpiration
strict consensusa method
for choosing among several most parsimonious trees generated by a
phylogenetic analysis; strict consensus means that only clades that show
up in all the most parsimonious trees are recognized
strobilus, strobilicone; an
aggregation of sporophylls on a common axis
symplesiomorphy, symplesiomorphic
traitshared primitive
trait (plesiomorphy)
synangium, synangiaa
reproductive unit composed of fused sporangia
synapomorphyshared
derived trait (apomorphy); a derived character that is shared
between organisms; compare to autapormorphy
systematicsfield of
biology that deals with the grouping and organizing of organisms
taxic
homologycorrespondence in structure between sister groups; for example fronds
of ferns and leaves of dicots are taxic homologies, i.e. they are derived
structures from the same primitive structure of the common ancestor of
these two groups
taxonomythe naming of
organisms and groups of organisms
toothed margin
(leaves)margin having projections or serrations with
pointed apices, indented less than one quarter of the distance to the
midvein or long axis of the leaf; compare entire margin and lobed margin
leaves
tracheida water conducting
and supportive cell type of xylem composed of
long, thin cells with tapered ends and walls hardened with lignin
tracheophyteplants with
true vascular tissue, i.e. xylem and phloem; compare to leptoids
and hydroids
transformational
homologyan evolutionary series of character states with
no significant breaks (from the plesiomorphic
ancestor to the apomorphy in the descendant)
transverse sectioncross
section; a section perpendicular to the longitudinal axis of the plant
organ
triarchconsisting of three;
for example a triarch stele has three lobes
unifacial (vascular
cambium)having one "face", i.e. a cambium that produces cells only on one side; a
unifacial vascular cambium that produces only secondary xylem is found in
some fossil non-seed plants; compare to bifacial
vascular cambium and vascular cambium;
vallecular canalair-filled
canals in the cortical (cortex) tissue of some
sphenophytes that alternate with the vascular
bundles
vascular bundlea strand
of tissue composed mostly of xylem and of phloem;
vascular cambiuma
lateral meristem that produces secondary vascular
tissue in stems and roots; see cambium and bifacial and unifacial
vascular cambium
vascular tissuetissue
composed of conducting cells, i.e. xylem and phloem
vessel elementa water
conducting, specialized short, wide cell in angiosperms; vessel elements
are arranged from end to end in a tube-like fashion; the perforated or
open ends of the vessel elements allow water to pass freely; a type of xylem tissue; compare to tracheid
vicarianceseparation of a
continuously distributed ancestral population or species into separate
populations, due to the development of a topographic or ecological barrier
wood raya radially oriented
tier of parenchyma cells that conducts food, water, waste products and
other materials laterally in stems and roots of woody plants; rays are
ususally continuous across the vascular cambium between the secondary phloem and xylem
xylemtissue through wich
most of the water and dissolved minerals utilized be a plant are
transported; see vessel elements and tracheids
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