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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 actinostele
a type of protostele that looks like a star in cross section allochtonous
something that has been transported amphiphloic
having 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) annulus
specialized 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 antheridia
reproductive structure that produces male gametes (sperm) anthracite
see coal apical meristem
embryonic, totipotent tissue in the tips of the roots and shoots of plants apomorphy
same as derived trait archegonia
reproductive structure that produces female gametes (egg) ataxonomic
an 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 autapomorphy
derived trait or apomorphy that is unique to only one group or OTU autochtonous
something that has not been transported axis
see stem basal taxon / group
a 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 biocoenosis
life assemblage; an assemblage of fossils that reflects associations characteristic of the community when it was living bisaccate
a pollen grain with two sacci biseriate
in two ranks or rows in the same plane bituminous coal
see coal cambium
a lateral meristem that produces secondary growth carbonate
a 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 canal a ca nal in the xylem of some sphenophytes, for example Equisetum, that results from extension and rupture of the protoxylem elements carpel
the female reproductive organ of a flower, consisting of stigma, style and ovary cast
opposite of mold; a preservation type that forms within a mold; casts are usually three-dimensional and therefore preserve form cellulose
polysaccharide that consists of a long unbrached chain of glucose units; cellulose is the main constituent of the cell walls of most land plants character
heritable 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 reversal
character that reverses to a more ancestral state character state
the state or value of a character; for example some character states for the character 'color' are red, green and blue chert
a 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 clade
a group of organisms that share a common ancestor; lineage; a monophyletic group cladistics
same as phylogenetic systematics cladogram
a 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 coal
a 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 balls
a 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. collenchyma
tissue 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 compaction
in 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 cell
a 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 tissue
tissue that consists of more than one cell type, e.g. phloem compression
a fossil preservation type in which a thin film of organic matter is preserved; compare to impression cone
see 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 cork
a 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 cambium
a narrow cylindrical sheath of meristematic cells that produces cork cells to replace the epidermis during secondary growth (growth in width) cortex
a primary tissue composed mainly of parenchyma cells, which extends between the epidermis and the vascular tissue cotyledon
the 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 crozier the spirally coiled "fiddlehead" of an immature fern leaf cupule
structures that surround one or more ovules or seeds; the cupule lobes may be free or united cuticle
an impermeable layer of cutin on the outer walls of epidermal cells cutin
the waxy substance of which a cuticle is composed deciduous
falling off; in plants: shedding leaves annually decussate branching
a 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 trait
same 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 growth
a 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 branching
a 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 dictyostele
a dissected siphonostele with two or more overlapping leaf bases dioecious
having 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 distribution
discontinuous distribution of a species disparity
distinct in morphological characters; morphological variation; compare to diversity dispersal
to disperse: to dispel or scatter; in plants dispersal refers to mechanism of dispersing reproductive propagules like seeds or pollen diversity
a 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 integument
the two outermost layers of an ovule in angiosperms, one of which will differentiate into the seed coat; see integument ectophloic
having phloem only on the outer side of the stele; compare to amphiophloic embryophyte
the group of all organisms that retain the zygote on the parent to form an embryo enation
a non-vascularized, epidermal outgrowth found in some early land plants endarch
a 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 endemic
belonging 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 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) endosporic
gametophyte develops within the spores wall; compare with exosporic endotesta
the 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 epidermis
the exterior tissue, usually on cell thick, of leaves and young stems and roots Euphyllophytina
clade 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, eusporangiate
eusporangium: sporangium that arise from a group of superficial cells; this is the primitive character state in vascular plants; compare to leptosporangium eustele
a 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; 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 evergreeen habit is not restricted to conifers evolutionary grade
same as paraphyletic groupshowing similarities in morphology, ecology or life history evolutionary systematics
same 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 exine
the outermost layer of the wall of pollen and spores; made of sporopollenin; compare to intine exosporic
gametophyte development outside the spore wall, i.e. the development of a free-living, multicellular gametophyte extant
currently existing; living now extinct
no longer existing; not living anymore fiber
a long-walled plant cell which is often dead at maturity; fibers impart elasticity, flexiblility and tensile strength to plant structure 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 form taxon
binomial 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 fossil
any evidence of past life; any remains of any once living organism preserved in the Earth's rocks frond
leaf of a fern fusain
fossil charcoal; a component of coal and sedimentary rocks characterized by black color, silky luster and fibrous texture fusiform
tapering towards each end; football-shaped gametophyte
the haploid phase (n=1) of a life cycle on which gametes are produced grade
see evolutionary grade ground tissue
a tissue consisting mostly of parenchyma cells that makes up the bulk of a young plant growth form
general description of the type of growth exhibited by a plant, such as herbaceous, shrubby (bush-like) and arborescent (tree-like) heterochrony
an evolutionary change in phenotype based on an alteration in timing of developmental events heterosporous
having two types of spores: megaspores and microspores homologous, homology
homology: likeness and correspondence in structure between parts of different organisms, due to common ancestry of the organisms; compare to analogy; homoplasy
same as convergence; homosporous
having one type of spore hydroid
the water conducting cells of bryophytes; compare to leptoid impression
a type of preservation that represents the negative imprint of an organism; compare to compression index fossil
a 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 integument
the 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) internode
the segment of a plant stem between the points where leaves are attached intine
the innermost layer of the wall of pollen and spores; made of cellulose and pectates; compare to exine leaf
a flattened, photosynthetic structure of a plant arranged on a stem leaf gap
a 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 trace
a branch of vascular tissue leading from the main vascular cylinder of the stem to a leaf leptoid
photosynthate conducting cells of bryophytes; compare to hydroid leptosporangium, leptosporangiate
leptosporangium: sporangium developed from a single superficial cell; leptosporangiate: having leptosporangia; this is a derived character state in the fern clade; compare to eusporangium lignite see coal ligule
a 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 shoot
shoots that are distinguished by their widely separated nodes and and internodes; compare with short shoot lumen
intercellular space manoxylic wood
wood type that contains abundant parenchyma; typical of cycads; compare with pycnoxylic massule
a large mass of mucilagenous material that encloses the microspores of water ferns like Azolla megagametophyte
in heterosporous plants and in seed plants: the female gametophyte produced by a megaspore megaphyll
a leaf with more than on vein and a leaf trace associated with a leaf gap in the stele; compare to microphyll megasporangium
a sporangium that produces megaspores; see also heterosporous megaspore
a large, haploid (N=1) spore of a heterosporous plant that produes a megagmetophtye (female gametophyte) meiotic
pertaining 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 meristem
region 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 mesophyll
parenchyma tissue between the upper and lower epidermis of a leaf metaxylem
a 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 microphyll
a 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 micropyle
a small opening in the integument at the apex of a seed through which either pollen (gymnosperms) or the pollentube (angiosperms) enters microsporangium
a sporangium that produces microspores; also see heterosporous microspore
a small, haploid (N=1) spore of a heterosporous plant that produces a microgametophyte (male gametophyte) midden, pack-rat midden
midden: 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 mold
a three-dimensional preservation type that represents a negative image of the plant; compare to cast molecular fossil
non-structural compounds, for example break-down products of pigments or lignins monocarpic
a 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 group
terms 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 monostelic
having one stele; compare to polystelic morphometrics
method 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 node
1. 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 nucellus
ovule tissue within which an embryo develops (embryo sac); homologous with the megasporangium of a seed plant numerical taxonomy
same 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 ontogeny
the course of development of an individual organism Operational Taxonomic Unit
see OTU order
or 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). OTU
or Operational Taxonomic Unit; definitions or names of the taxa included in a phylogenetic analysis overall similarity
a 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) ovary
the enlarged basal portion of a carpel, where the ovules are borne; the ovary differentiates into the fruit ovule
unfertilized seed; the ovule contains the megasporangium with the megagametophyte, surrounded by one or two integuments integument palynomorph
fossil spores and pollen; also dinoflagellates parallell evolution
see 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 parenchyma
the most common type of plant cell; thin-walled cells varying in size, shape, and function parichnos
an interconnected system of parenchymatous strands with many air spaces that extend throughout the vegetative organs of some arborescent lycopsids parichnos scars
small scars that marks the position of the parichnos strands on stem fossils of the some arborescent lycopsids peat
see coalaccumulations of terrestrial organic material with little associated mineral sediment periderm
a tissue primarily consisting of cork cells; outer bark permineralization a preservation type in which mineral matter has infilled intercellular and intracellular spaces, but has not replaced the cell walls; compare to petrifaction
and silification
petal
one of the whorls of a flower; petals may be brightly colored petiole
the stalk of a leaf petrifaction
a type of preservation in which mineral matter infills intercellular spaces and replaces the cell walls; compare to permineralization and silification phenetics, phenetic systematics
same as numerical taxonomy phenetic similarity
same as overall similarity phloem
photosynthate conducting tissue of vasular plants phosphate
PO34-; a mineral that often participates in permineralization phylogenetic character
see character phylogenetic systematics
same as cladistics; a method of grouping organisms that is basedsynapomorphies or shared derived traits or characters; compare to numerical taxonomy phylogeny
an hypothesis of evolutionary relationships among organisms; the pattern of lineage branching produced by the evolutionary history of the organisms considered physiognomy, foliar physiogonomy
analysis of leaf features that are sensitive to environment pinnae
plural: (primary) pinna; first order of subdivision of a compound leaf or fern frond pinnule
the second order of segments of a compound or dissected leaf leaf or frond pith
the central parenchymatous tissue in a vascular plant axis platyspermic
a flattened seed with bilateral symmetry plesiomorphy, plesiomorphic trait
same as primitive trait polarity
direction of evolutionary change; evolutionary order, i.e which character state follows another in a character transformation series pollen
the microspore of seed plants that contains the microgametophyte (male gametophyte) pollination
the 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 group
a group of organisms with different most recent ancestors polystelic
having more than one stele primary growth
growth in length, controlled by the apical meristem primary pinnae
leaflet of first subdivsion of a fern frond or compound leaf primitive trait
same 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 procambium
the 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 protoxylem
the 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 wood
dense wood that contains little parenchyma; typical of Archeopteris conifers; compare to manoxylic pyrite
FeS2 a common mineral that participates in permineralization quadriseriate
in four ranks or rows; for example see branching radiospermic
a round seed; a seed with radial symmetry rhizome
a (usually) underground stem that is horizontally oriented; rhizomes may appear like roots, but have a definite node and internode architecture root
a plant organ that functions in anchorage and absorption; in seed plants derived from a bipolar embryo saccate pollen
pollen with a saccus or sacci; characteristic of many conifers saccus/sacci
a winglike or bladderlike extension on a pollen grain; sarcotesta
the usually parenchymatous outer layer of the integument in some seeds; see also endotesta and sclerotesta sclereid
a short, irregular sclerenchyma cell with pits; sclereids function as tissue support sclerenchyma
tissue composed of cells with walls thickened with lignin; sclerenchyma tissue functions primarily in strengthening and support sclerotesta
the middle, fibrous layer of the integument in some seeds; see endotesta and sclerotesta secondary growth
growth in width initiated and maintained by the vascular cambium and cork cambium secondary xylem
xylem produced by the vascular cambium, see also xylem, and compare with primary and secondary growth seed plants
a 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 seed
a fertilized ovule; megasporangium that contains an embryo enclosed in an integument segment
individual divisions on a pinnule sepal
a 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 shoot
shoots that are characterized by short internodes giving the shoot a crowded appearance; compare with long shoot sieve cell
a phloem conducting cell type in all vascular plants except angiosperms sieve plate
area 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 silification
a type of fossilization in which silica (SiO2) infills intercellular spaces (permineralization) or replaces the cell walls (petrifaction ) silica
SiO2; 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 tissue
tissue composed of only one cell type siphonostele
a type of stele that consists of a ring of vascular tissue surrounding a pith sinus
the indentations of a lobed pinna / segment of a fern or of a dicot leaf sister group
two 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 sporangiophore
the stalk which terminates in a sporangium is produced sporangium, sporangia
structure in which spores are produced spore
a haploid (1N) reproductive cell capable of developing directly into a gametophyte without uniting with another cell sporophyll
a modified leaf bearing sporangia sporophyte
the spore producing, diploid (2N) phase of the life cycle; compare to gametophyte sporopollenin
an organic polymer that makes up the coat of a pollen grain or spore; sporopollenin is extremely resistant to degradation stele
the central vascular cylinder in stems and roots where the vascular tissue is located stem
same as axis; a plant axis with leaves or enations stoma, stomata
a 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 consensus
a 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, strobili
cone; an aggregation of sporophylls on a common axis symplesiomorphy, symplesiomorphic trait
shared primitive trait (plesiomorphy) synangium, synangia
a reproductive unit composed of fused sporangia synapomorphy
shared derived trait (apomorphy); a derived character that is shared between organisms; compare to autapormorphy systematics
field of biology that deals with the grouping and organizing of organisms taxic homology
correspondence 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 taxonomy
the 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 tracheid
a water conducting and supportive cell type of xylem composed of long, thin cells with tapered ends and walls hardened with lignin tracheophyte
plants with true vascular tissue, i.e. xylem and phloem; compare to leptoids and hydroids transformational homology
an evolutionary series of character states with no significant breaks (from the plesiomorphic ancestor to the apomorphy in the descendant) transverse section
cross section; a section perpendicular to the longitudinal axis of the plant organ triarch
consisting 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 canal
air-filled canals in the cortical (cortex) tissue of some sphenophytes that alternate with the vascular bundles vascular bundle
a strand of tissue composed mostly of xylem and of phloem; vascular cambium
a lateral meristem that produces secondary vascular tissue in stems and roots; see cambium and bifacial and unifacial vascular cambium vascular tissue
tissue composed of conducting cells, i.e. xylem and phloem vessel element
a 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 vicariance
separation of a continuously distributed ancestral population or species into separate populations, due to the development of a topographic or ecological barrier wood ray
a 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 xylem
tissue through wich most of the water and dissolved minerals utilized be a plant are transported; see vessel elements and tracheids
这些都是UCMP里的古植物学的专业词汇，有的时候看外文文献一些苦涩的专业词汇只能借助这些词汇表才能摸清楚一二。 | 
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