Glossary - general

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Ob- – against, as a botanical prefix usually indicating “the other way round from the usual” (e.g. ovate is egg-shaped, whereas obovate is egg-shaped with the attachment point at the base and the widest part near the top)

Obclavate – clum-shaped, with the thicker end near the attachment point

Obconical – conical with the narrow part near the base and the wide part near the apex

Obcordate – heart-shaped, with the narrow end near the base and the wider, notched end near the apex

Obdiplostemonous androecium – with the stamens in two whorls, twice as many as the petals, the outer alternate with the outer perianth whorl, the inner alternate with the inner perianth whorl

Obdiplostemony – see Obdiplostemonous androecium

Obhaplostemonous androecium – with the stamens in one whorl, as many as the petals or the sepals and opposite the inner perianth whorl if present

Obhaplostemony – see Obhaplostemonous androecium

Oblanceolate – narrowly obovate and tapering to a point at both ends

Oblate (of a globose shape) – flattened at the poles

Obligate life form or habitat requirement – restricted to this life form or habitat and not occurring as or in any other – Opposite: facultative

Oblique – (1) (of leaf) when the two sides of the leaf are unequal near the base; (2) (of ovary) when the ovary is at an angle to the axis or plane of symmetry of the flower

Oblong (of a plane shape) – longer than broad, with the margins parallel for most of their length

Obovate – egg-shaped (two-dimensional) with the broadest part near the apex

Obovoid – egg-shaped (three-dimensional) with the broadest part towards the apex

Obpyriform (of a three dimenisonal shape) – like an inverted pear, i.e. with the broadest part proximal

Obreniform – kidney-shaped, with the point of attachment at the rounded side, not in the sinus

Obsolete – rudimentary

Obtriangular (of a two-dimensional shape) – like an inverted triangle, i.e. with the narrowest part proximal

Obtrullate – obverse of trullate, shaped like a bricklayer’s trowel

Obturator – (1) small body with pollen mass; (2) process of ovary wall descending on the micropyle (funicular obturator, integumentary obturator, placental obturator) – see also Ponticulus

Obtuse – of an apex or base, not pointed, blunt

Ocreola, ochreola – the reduced ocrea (ochrea) of an inflorescence

Ocrea, ochrea – 1) of a leaf sheath, an extension beyond the petiole insertion (e.g. in Arecaceae); 2) a tubular stipule sheathing the stem (e.g. in Polygonaceae)

Ocreate, ochreate – with an ocrea (ochrea)

Odorous – smelling; producing a smell

Offsetting – producing a lateral shoot for propagation purposes

Oil cell – a type of idioblast containing and secreting oils (lipids, ethereal oils, etc., secreted by plastids); oil cells frequently have a suberized cell layer between the cellulose layers

Oleaginous – oily

Oleo-resin – natural mix of a resin and an essential oil, forming a balsam or turpentine

Oligarch vascular bundles – containing few fibro-vascular bundles; vascular bundle with few rays

Omniaperturate pollen grain – the exine is very thin or absent and the intine thick, so that no specific apertural region can be distinguished and thus the whole surface can be considered apertural in nature

Onagrad embryogenesis – a vertical wall in the apical cell and a transverse wall in the basal cell give rise to a T-shaped tetrad; the apical cell contributes to the major portion of the embryo; the hypophyseal region (producing the initials of the root cortex and root cap and completing the embryo) is derived from the basal cell

Opaque – not translucent or transparent; impenetrable to light

Open aestivation – apert aestivation; the margins of adjacent (usually reduced) sepals/petals do not touch each other

Operculate – with a lid

Opercule, operculum – a lid or cover

Operculum (of fruit) – a lid-like covering of a pyxidium, which detaches when the fruit is ripe

Operculum (of leaf) – (Cephalotaceae, Nepenthaceae, Sarraceniaceae) the leaflet preventing a pitcher from a surplus of rainwater

Operculum (of pollen grains) – a thickened, distinctly delimited structure of the ectexine or sexine, which covers a part of an ectoaperture

Operculum (of seed) – a lid-like hard structure on the seed coat, which becomes detached during the germination

Opposite – (1) (of leaves and branches) when two are borne on the same node but on diametrically opposed sides of the stem; (2) (of other organs) when placed e.g. in front of the petals instead of alternating with them

Opposite lateral wall pitting – intervascular pits forming lateral series on vessel walls, not spirally but horizontally distributed, either on vessel-vessel interfaces or on vessel-ray interfaces

Oppositipetalous – see Antepetalous

Oppositisepalous – see Antesepalous

Opposititepalous – see Antetepalous

Orbiculate – disc-shaped

Orbicular – (1) (two-dimensional) with a circular outline; (2) (three-dimensional) globose

Orientation – relative position, place

Orifice – opening, mouth

Ornamented pollen grain – with sculpturing on the surface (e.g. spines, tuberculae, reticulations, granules) – Opposite: psilate, smooth

Orthoamphitropous ovule – a type of amphitropous ovule, in which the trace proceeds straight to the megasporangium via the basal body

Orthocampylotropous ovule – a type of campylotropous ovule, in which the trace proceeds straight to the base of the megasporangium

Orthostichy – a vertical line joining an organ to the next organ immediately above it on the stem

Orthotropic shoot – vertical branch or stem; distinct from plagiotropic

Orthotropous ovule or seed – with a straight axis, the base of the funicle proximal, the micropyle distal

Os (of pollen grains) – endoaperture

Osmophore – a type of gland, in which the floral fragrance originates (produced and released); various floral parts may be differentiated as osmophores; osmophores consist of glandular tissue usually several cell layers in depth, the outer epidermal layer possessing stomata

Osseous – bony

Osteosclereid – elongated sclereid with swollen ends

Ostiolar – of the mouth, e.g. ostiolar bracts, those at the ostiole of a fig

Ostiole – mouth, as in the aperture at the apex of a fig

Oval – broadly elliptic; ‘elliptic’ is a better term

Ovary – the ovule-bearing part of the gynoecium; the (usually enlarged) part of the pistil which contains the ovules and eventually becomes the fruit

Ovate – egg-shaped (two-dimensional), about twice as long as broad, with the wider part below the middle

Ovoid – egg-shaped (three-dimensional), with the broad part below the middle/nearest the base

Ovule – the immature seed in the ovary before fertilization; comprises the funicle, chalaza, inner (tegmen) and outer (testa) integuments, nucellus (megasporangium) and embryo sac (megagametophyte)