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Term	Definition
Ocrea	A structure formed of stipules fused into a sheath and surrounding the stem; i.e., a diagnostic character of the Polygonaceae; in palms, an extension of the leaf sheath beyond the petiole insertion, is a different kind of ligule.
Odd-pinnate leaf	Pinnate with an odd number of leaflets; i.e., without a terminal leaflet. Same as imparipinnate.
Opercular opening	The opening of a dehiscent-fruited species of Lecythidaceae.
Opercular rim	The circular scar that indicates where the operculum was attached to the fruit.
Operculate	Possessing an operculum. Same as lid.
Operculum	The lid of the fruit of species with circumscissilely dehiscent fruits as found in many species of Lecythidaceae; a valvelike opening into the stony endocarp of the fruit of some species (e.g., Humiriaceae); referring to a seed with an opening covered by a lid (e.g., Zingiberaceae) or the membranous cover of the nectary in Passiflora (Passifloraceae).
Operculum (plural = opercula)	Lid-like; the lid of a dehiscent fruit as found in many, but not all, Lecythidaceae.
Opposite	Arising from an axis, such as leaves from a stem, in pairs at the same node. Compare with alternate and whorled.
Opposite leaves	Reffering to leaves that arise from an axis in pairs at the same node. Compare with alternate and whorled.
Opuesta	Se refiere a la disposición de las hojas, cuando están en pares, insertas una a cada lado en un mismo nudo. Comparar con alterna y verticilada
Oral setae	Coarse, bristlelike appendages present at the summit of the leaf sheaths of some grasses.
Orbicular	Referring to a two-dimensional structure with a circular outline.
Orbiculate	A an orbiculate shape is widest at the middle and possesses a length to width ratio of greater than 1.1:1 to less than 1.2:1 Based on Hickey (1973). For more information about leaf morphology and leaf architecture see Ellis et al. (2009).
Ostiole	The opening into the syconium (fig) of Ficus (Moraceae).
Outcrossing	In flowering plants, the production of viable seed by the movement of pollen from one plant to another plant.
Outer bark	Dead tissue surrounding branches, trunks, and roots that includes all tissue from the innermost periderm outward.
Outer bark	All tissue of the trunk and stems produced by the cork cambium, this includes the phelloderm, the cork cambium or phellogen, and the cork or phellum (the dead bark tissue).
Outer bark laminated	The outer bark has distinct lines as seen without magnfication. This feature is seen only by making a slash of the bark.
Outer bark smooth	Bark without fissures, scallops, or roughness.
Outer bark thick	The outer bark is markedly thicker than the inner bark.
Outer bark thin	The outer bark is thinner than the inner bark.
Ovary	The part of the gynoecium (=pistil) containing the ovules.
Ovary	The part of the gynoecium containing the ovules.
Ovary cross-section	A section through the ovary made at a right angle to the long or vertical axis of a flower. A term used in the Lecythidaceae to determine the number of locules and to describe the placention of species and genera.
Ovary half-inferior	An ovary of Lecythidaceae that bulges upward at the summit making the ovary appear half-inferior in contrast to an inferior ovary which is truncate at the apex..
Ovary inferior	An ovary in which the other floral parts (calyx, corolla, and stamens) arise from the summit of the ovary.
Ovary summit	The area at or above the inside of the staminal ring.
Ovary summit obconical	If the summit of the ovary slants upward directly on the inside of the staminal ring (i.e., the summit completely fills the inside of the staminal ring) the summit is obconical. Obconical ovary summits can be narrowly or broadly obconical.
Ovary summit plateau-like	The apex of the ovary sits on a raised plateau characterized by erect sides.
Ovary summit truncate	Appearing to be cut off at the apex, i.e., disregarding the style the summit of the ovary is flat.
Ovary summit umbonate	If the summit of the ovary arches upward directly on the inside of the staminal ring (i.e., the summit completely fills the inside of the staminal ring) the summit is umbonate. See style umbonate.
Ovate	Ovate refers to a leaf, sepal, petal, or other flat structure that is wider at the base than at the midpoint, tapers toward the apex, and has a length-to-width ratio of 1.5:1 to less than 2:1.
Ovoid	Egg-shaped; the three-dimensional version of ovate.
Ovule	The organ that after fertilization becomes the seed. The ovule in angiosperms contains the embryo sac with an egg cell, several other cell types, and is enclosed within the locule of the ovary.
Ovule	The organ that contains the egg and, after fertilization, becomes the seed. The ovules are included within locules of an ovary and are attached to the placenta in different ways that, in some cases, are generic specific.
Ovule anatropous	Referring to a curved downward ovule in such a way that the micropyle is close to the funicular attachment.
Ovule bitegmic	An ovule with two integuments.
Ovule campylotropous	Referring to an ovule in which the axis is at an approximately right angle to its stalk (funicle).
Ovule columns	The number of vertical lines of ovules from the base to the apex of the placenta. The number of horizontal layers of ovules in a locule. A longitudinal section that removes the outside wall of a locule allows this feature to be seen with the most accuracy. It can also be observed in a medial longitudinal section. A longitudinal section that removes the outside wall of a locule allows this feature to be seen with the most accuracy. It can also be observed in cross sections through the placenta.
Ovule insertion	Referring to where ovules are inserted along the lower septum as viewed in longitudinal section.
Ovule orientation horizontal	Refers to an ovule that departs from the middle part of the placenta at a more-or-less 90 degree angle as seen in longitudinal section.
Ovule orientation oblique	An ovule that departs from the middle part of the placenta at an angle less than 90 degrees as seen in a longitudinal section. The angle is the upper angle of a line drawn through the ovules and intersecting with the vertical axis of the ovary as seen in longitudinal section.
Ovule orientation pendulous	An ovule that departs from a poorly developed placenta that hangs downward at the apex of the locule as seen in a longitudinal section of the ovary.
Ovule orthotropous	Referring to a straight ovule in which the micropyle is positioned in a straight line and opposite the funicular attachment; referring to a growth habit in which the growing apex is oriented vertically.
Ovule rows	The number of horizontal layers of ovules in a locule. A longitudinal section that removes the outside wall of a locule allows this feature to be seen with the most accuracy. It can also be observed in a medial longitudinal section. A longitudinal section that removes the outside wall of a locule allows this feature to be seen with the most accuracy.
Ovule unitegmic	An ovule with one integument.
Ovules	Structures that arise from placentae in the ovary locules. Among other cells, the egg and two polar nuclei are found in the ovule. After fertilization, the egg develops into an embryo and the polar nuclei develop into endosperm which, along with the seed coat, form the seed..
Ovules anatropous	Referring to a curved downwardly oriented ovule in such a way that the micropyle is close to the funicular attachment.
Ovules bitegmic	An ovule with two integuments.
Ovules horizontally oriented	Ovules projecting outward at right angles from the vertical axis of the ovary.
Ovules obliquely oriented downward	—
Ovules obliquely oriented upward	Ovules projecting upward at less than right angles from the vertical axis of the ovary.
Ovules pendulous	Ovules that hang downward from the septum at apex of the locule with the micropyle facing upward.
Ovules tenuinucellate	The presence of no cells or a single cell layer between the megasporophyte and the epidermal cells in the early development of the megasporophyte.
Ovules tenuinucellate	The presence of no cells or a single cell layer between the megasporophyte and the epidermal cells in the early development of the megasporophyte. The megasporophyte develops into the embryo sac which contains an egg that, if fertilized and the conditions are right, will develop into an embryo.
Oxidation	The process of using oxygen to break down glucose to obtain energy. This results in the production of carbon dioxide and water as by products. Carbon dioxide and water are also released when forests are burned resulting in the release of greenhouse gases in the atmosphere.
Pachycaul	A type of growth form in which the tree is unbranched (monocaulis) or sparsely branched, the stems are thick, and the leaves very large.
Pachycaul	A type of growth form in which the tree is unbranched (monocaulis) or sparsely branched, the stems are thick, and the leaves very large.
Pachycaulous	Referring to a growth form in which the branching is sparse and the higher-order branches and stems are not markedly diminished in thickness. Compare with leptocaulous.
Palea	The upper of the two bracts that enclose the floret in the Poaceae. Compare with lemma.
Palinactinodromous	Referring to a type of leaf venation in which the primaries have one or more subsidiary points of radiation above the lowest point.
Palisade mesophyll	Referring to one or more layers of cells located directly under the epidermal cells of the adaxial leaf blade surface. The palisade mesophyll is oriented vertically and is longer than broad. Photosynthesis takes place in both palisade and spongy mesophyll.
Palmate	Referring to leaf venation in which the main veins of the blade radiate from a common point near the base or to compound leaves in which all leaflets radiate from a common point. See digitate. palmately lobed, palmatilobate,
Palmately veined	Referring to leaf venation in which the main veins of the blade radiate from a common point near the base.
Palmatinervia	Se refiere a la disposición radial de los nervios que nacen desde un punto común en la base de una hoja
Panicle	A compound raceme in which the primary branches are racemose, which, in turn, give rise to secondary and sometimes higher order racemose branches.
Papilionaceous corolla	The zygomorphic corolla of most species of papilionoid legumes.
Papilla (plural = papillae, adj. = papillate)	Small projections that are often found on leaf blade surfaces. Papillae usually represent modifications of the cuticle.
Papilla (plural = papillae; adj. = papillate)	Referring to an abaxial leaf blade surface or a stigma that bears minute protuberances that appear to be outgrowths of the cuticle of the leaf blade or of the stigma.
Papillae	Minute, rounded protuberances that may cover a surface, e.g., the abaxial leaf blade surfaceae.
Pappus	A modified calyx of hairs, scales, or bristles typical of many Asteraceae.
Paracytic stomata	Referring to a stomatal type in which the two subsidiary cells are parallel to the long axis of the guard cells. The brachyparacytic type is the same as the paracytic type.
Paracytic stomata	Referring to a stomatal type in which the two subsidiary cells are parallel to the long axis of the guard cells. The brachyparacytic type is the same as the paracytic type.
Parallel venation	Generally applied to secondary or higher-order veins that are parallel to each other and to the margins of the leaf, sepal, or petal in which they occur but in monocots they are often numerous primary veins of the same size.
Parallelodromous	Referring to a leaf venation in which there are multiple parallel primary veins that originate at the leaf blade base and converge toward the leaf blade apex. Mostly restricted to monocotyledons. See Ellis et al. 2009 for more detailed descriptions of leaf characters.

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