Australian Biological Resources Study
Compiled by A.McCusker
obconical: cone-shaped but attached at the narrower end.
obcordate: of a leaf blade, broad and notched at the tip; heart-shaped but attached at the pointed end.
oblanceolate: similar in shape to lanceolate but attached at the narrower end.
obligate: of parasites, unable to survive without the host. cf. facultative.
oblique: of a leaf or leaflet, larger on one side of the midrib than on the other, i.e. asymmetrical. > image <
obloid: a three-dimensional shape, with short, parallel sides and rounded ends, as if composed of two hemispheres linked together by a short cylinder.
oblong: a two-dimensional shape, having the length greater than the width but not many times greater, and the sides parallel. > image <
obovate: similar in shape to ovate but attached at the narrower end. > image <
obovoid: similar in shape to ovate, but attached at the narrower end.
obsolescent: non-functional but not reduced to a rudiment.
obsolete: reduced to a rudiment, or completely lacking. cf. rudimentary, vestigial.
obtuse: blunt or rounded at the apex, the converging edges separated by an angle greater than 90 degrees.
ochrea: a sheath, formed from two stipules, encircling the node in Polygonaceae. > image <
ontogeny: the development of a single organism, i.e. the sequence of stages through which it passes during its lifetime.
operculum: in a flower, a cap formed by fusion or cohesion of perianth parts and covering the stamens and carpels in the bud, becoming detached at maturity by abscission; especially in Eucalyptus, see calyptra. > image | image <
opposite: of leaves or other lateral organs, borne at the same level but on opposite sides of the stem; of floral parts, on the same radius. cf. alternate. > image <
orbicular: circular or nearly so. > image <
order: a taxonomic grouping of families believed to be closely related (sometimes a single family with no apparent close relatives); the major taxonomic rank between family and class.
orthotropous: of an ovule, erect so that the micropyle points away from the placenta.
ostiole: an opening or pore, e.g. at the apex of a fig.
ovary: the basal portion of a carpel or group of fused carpels, enclosing the ovule(s). > image <
ovate: a two dimensional shape, like a section through the long axis of an egg, and attached by the wider end. > image <
ovoid: egg-shaped (in three dimensions).
ovulate: with ovules.
ovule: a structure in a seed plant within which one or more megaspores are formed and which develops into a seed after fertilisation. > image <
ovuliferous: bearing ovules, e.g. applied to scales in a megasporangiate cone in gymnosperms.
ovulode: sterile structures on the placenta.