Terminology
The page contains terminology and select topics related to paleobiology that are used on this website.
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- The origin of roots
Terminology
Abaxial
The bottom surface of a leaf; the underside
Acritarchs
Decay-resistant organic-walled microfossils from unicellular photosynthetic protists, especially during the Proterozoic
Adaxial
The upper surface of a leaf; the topside
Anatropous
An ovule recurved so that the micropyle is bent back toward the stalk (funiculus)
Anistomous
Dichotomous branching in which resulting branches are unequal in angle and usually girth. See branching patterns.
The pattern and mechanism by which the apical cell, or meristem, of a plant stem produces branches.
e.g. dichotomous (isotomous, anisotomous, pseudomonopodial), monopodial
Centrarch
A pattern of maturation in which xylem cells develop from the center of a vascular strand or stem toward the outside (centrifugally); see xylem maturation
Centrifugal
Moving or developing away from a center
Centripetal
Moving or developing toward the center
Cone
A reproductive structure with aggregated seeds or spores on modified stems and/or leaves; also called a strobilus
Compound cone: A cone constructed with seeds attached to lateral stems (e.g. female pine cones)
Simple cone: A cone constructed with seeds attached to lateral leaves (e.g. cycad cones, male pine cones)
Decussate
An opposite branching pattern in which pairs of leaves (or axes) are 90 degrees apart with each set or at each node. See branching patterns.
Dichotomous
Splitting into two parts, such as branching; see branching patterns.
Dioecious
Plants that have separate male and female individuals
Distichous
A "two-ranked leaf arrangement" where the leaves (or axes) on a stem are arranged in two vertical columns on opposite sides of the stem. See branching patterns.
Distil
Toward the tip of a plant part; compare to proximal
Enation
Out-growth of a stem's epidermis that may appear leaf-like, but lacks vascular tissue; therefore it is not a leaf
A hypothesis proposed by F.O. Bower for the evolution of leaves, especially microphylls
Endarch
A pattern of maturation in which xylem cells develop from the inside of a vascular strand toward the outside (centrifugally); see xylem maturation
Euphylls
Leaves with complex, branching veins in the blade; feature of the euphyllophyte clade; also called megaphylls
Exarch
A pattern of maturation in which xylem cells develop from the outside of a vascular strand toward the inside (centripetally); see xylem maturation
Homosporous
Producing spores that are all the same size (compare to heterosporous)
Heterosporous
Producing two types of spores (i.e. megaspores and microspores) that are different in size
Isotomous
Dichotomous branching in which both branches are of equal angle and girth, forming a Y-shaped appearance; See Branching Patterns
Ligule
Small flap of tissue found above (adaxial) the microphylls of certain lycopsids (e.g. protolepidodendrids, isoetales). It is also found in grasses and sedges.
Lycophylls
Leaves with a single, unbranched vein in the blade. Feature of the Lycopsid clade; also called microphylls
Wood contain a mix of xylem cells and parenchyma cells; found in cycads and many seed ferns (see pycnoxylic wood)
Megaphyll
Leaf with a complex, branching veins in the blade. Feature of the Euphyllophyte clade; also called euphylls
Megaspore
Larger spores produced inside a megasporangium on a heterosporous plant, which give rise to female gametophytes (compare to microspore)
Mesarch
A pattern of maturation in which xylem cells develop from the middle of a vascular strand in both directions, radially; see xylem maturation
Microphyll
leaf with a single, unbranched vein in the blade. Feature of the Lycophyte clade; also called lycophylls
Microspore
Smaller spores produced inside a microsporangium by a heterosporous plant, which give rise to male gametophytes (compare to megaspore)
Monoecious
Male and female structures on the same individual
Monopodial growth
Orthotropous ovule
A completely straight ovule with the micropyle at the apex and away from the stalk (funiculus)
Pedicel
A small stalk bearing an individual reproductive structure, such as a flower or sporangium
Proximal
Toward the base of a plant part (compare to distil).
Wood with xylem cells and mostly devoid of parenchyma; found in conifers and angiosperms. (compare to manoxylic wood)
Pseudomonopodial
Branching in which one branch remains perpendicular to the ground, and the other(s) are angled to be parallel to the ground. See Branching Patterns
Pteridosperms
Also called "seed ferns" are a polyphyletic grouping of extinct plants that possessed both fern-like foliage and seeds. e.g. Calamopityales†, Lyginopterids†, Medullosids†.
Quadriseriate
Branching in four ranks or rows (e.g. Pertica †, Rhacophyton †, Stauropteris †); subsequent branching systems (pinnae) in two rows and at 90-degree angle
Recurvation
A developmental pattern in which a stem curves or curls back toward the main stem or trunk; usually terminal stems with reproductive structures.
Sporangium
A spore case or spore sac. The sporangium is the site of meiosis where (diploid) spore mother cells become (haploid) spores
Eusporangium: Large sporangium (visible to the eye) with 1,000s of spores which develops from a group of cells. These spore cases are found in "ancient ferns" such as the Psilotales, Marattiales, Ophioglossales, and even the Equisetales. Compare with leptosporangium
Leptosporangium: Microscopic sporangium with an annulus and 100s of spores that develops from a single initial cell. These spore cases are found in modern ferns in the Polypodiidae. Compare with eusporangium
Sporophyll
A specialized fertile leaf that protects and/or supports the sporangia or seeds of a plant
Stomata
Pores (stoma) that are found in the leaves and herbaceous stems of plants, which are surrounded by guard cells that regulate the opening and closing of the stoma. The opening of stomata allows for carbon dioxide to enter, and oxygen and water vapor to exit.
Cyclocytic pattern: The stomata are surrounded by four or more subsidiary cells arranged in a narrow ring around the stoma. e.g., Palms, Gigantopterids
Haplocheilic: Type of stoma in which the 2 guard cells are derived from a single mother cell and the subsidiary cells are derived from a different initial e.g., Pteridosperms, Cycads, Ginkgo, Conifers, Ephedra, and some angiosperms (Taylor & Taylor 1993)
Syndetocheilic: Type of stoma in which the 2 guard cells and the subsidiary cells are all derived from a single mother cell e.g., Bennettitales, Pentoxylon, Gnetum, Welwitschia, and some angiosperms (Taylor & Taylor 1993)
Strobilus
A reproductive structure with aggregated seeds or spores on modified stems and/or leaves; also called a cone
Tetrastichous
Axes, branches, or leaves arranged in four vertical rows
The pattern in which xylem and phloem are arranged inside of a plant. Usually displayed as the pattern observed in cross-section of the stem.
The pattern in which water conducting cells (xylem) mature within the cross-sectional plane of the stem. e.g. centrarch, endarch, exarch, and mesarch.