Terminology

Terminology

Abaxial

• The bottom surface of a leaf; the underside

Abiogenesis

• The process by which life arises from non-living matter, such as simple organic compounds. This process required a habitable world in the late Hadean, the abiotic synthesis of simple molecules, the eventual creation of protocells, and the Last Universal Common Ancestor (LUCA)

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.

Axis

• The cylindrical, stem-like structures on early land plants (e.g., Aglaophyton, Horneophyton)

• These axes are assumed to give rise to true stems, roots, and possibly leaves 

Branching Patterns

• The pattern and mechanism by which a plant stem's apical cell, or meristem, 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

Chert

• A hard, fine-grained sedimentary rock. It is composed of microcrystalline quartz

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 (sporophytic) individuals

• Dioicious: Gametophytes that have antheridia and archegonia on separate 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

Enation Concept

• 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

Manoxylic wood

• 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)

Meiosis

• The process by which a diploid cell (e.g., sporocyte) divides to create four haploid cells (e.g., spores). This process includes karyokinesis (separating of chromosomes) and cytokinesis (separation of cells).

• Simultaneous meiosis: This is meiosis in which the karyokinesis and cytokinesis occur at the same time; "typical" meiosis (e.g., plants)

• Successive meiosis: This is meiosis in which karyokinesis occurs first, and cytokinesis happens later (e.g., charophytes)

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 (sporophytic) individual

• Monoicious: antheridia and archegonia found on the same gametophyte

Monopodial growth

• See branching patterns

Orthotropous ovule

• A completely straight ovule with the micropyle at the apex and away from the stalk (funiculus)

Paleosol

• An ancient, fossilized soil

Paravascular

• Plants that lack true vascular tissue. They possess water-conducting cells that lack lignin (e.g., hydroids), and/or they possess sugar-conducting leptoids

• e.g., Horneophyton, Aglaophyton, eophytes

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).

Pycnoxylic wood

• 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

Taphonomy

• The study of how organisms decay and become fossilized or preserved in the paleontological record

Tetrastichous

• Axes, branches, or leaves arranged in four vertical rows 

Trilete mark

• A Y-shaped mark on spores of particular plant groups, which indicates simultaneous meiosis

• The mark is formed from the four spores pressing on each other during formation

Vascular Stele Architecture

• The pattern in which the xylem and phloem are arranged inside of a plant. Usually displayed as the pattern observed in the cross-section of the stem. 

Xylem Maturation

• The pattern in which water conducting cells (xylem) mature within the cross-sectional plane of the stem. e.g. centrarch, endarch, exarch, and mesarch.