Glossary R

r.h.
Relative humidity. raceme
An inflorescence consisting of a main axis, bearing single flowers alternately or spirally on stalks (pedicels) of approximately equal length. The apical growing point continues to be active so there is usually no terminal flower and the youngest branches or flowers are nearest the apex. This mode of growth is known as monopodial. racemose
Arranged like a raceme; in general any inflorescence capable of indefinite prolongation, having lateral and axillary flowers. rachis
The major axis of an inflorescence. radial (of leaves)
Arising from the base of a stem or from a rhizome; basal. radicle
The rudimentary root in an embryo. rainfall distribution See also rainfall intensity
The quantity of rain falling at different times of the year. In the tropics, rain may fall over 1 season only ('monomodal') or near the equator over 2 seasons ('bimodal', hence 1st and 2nd rainy seasons). rainfall intensity See also rainfall distribution
1. The rate at which rain is occurring at any given instant, usually expressed in millimetres per hour. 'Maximum rainfall intensity' refers to the rate during any time when the rate is both maximum and uniform. Usually one or more standard time periods, such as 5 or 10 minutes, are specified, and then the term refers to an average rate calculated from the amount that occurred during any such time period, although the rate was not necessarily uniform.
2. The amount of rain received per unit of time. Convection tropical storms often have a 'leading edge rate', that is, rainfall at the onset of the storm is greatest; it may be 150-200 mm/ha or more for a short period. rainforest
Generally, a forest that grows in a region of heavy annual precipitation. There are both tropical and temperate rainforests. ramet
An individual member of a clone. ramiflorous
Borne on the branches range
1. Land that produces primarily native forage suitable for grazing by livestock; also forest land producing forage. Usually relatively extensive areas of land suitable for grazing but not for cultivation, especially in arid, semi-arid or forested regions.
2. A unit of grazing land used by an integral herd of livestock.
3. The geographical area of occurrence of particular species of plants or animals. rangeland
Land suitable for grazing by domestic livestock. The vegetation consists mostly of native grasses, grasslike plants, forbs, shrubs. raphides
Calcium oxalate crystals present in bundles in some plant cells. ratoon
Sprouting or regrowth from buds or young tillers; crops originating from ratoon growth. ray (of wood)
Radial strands of living cells concerned with the transport of water and food. recalcitrant seed             See also orthodox seed
The seeds of some species have relatively short viability and cannot be stored in a dry condition or at low (subzero) temperatures. Some such seeds even suffer chilling damage. Examples are seeds of cocoa and rubber. recalcitrant seed storage behaviour
Mature whole seeds are unable to tolerate more than a limited amount of desiccation, for example to moisture contents in equilibrium at 20 deg. C with about 96-98% r.h. receptacle
Flat, concave or convex part of the stem from which all parts of a flower arise; the floral axis. recovery rate
Rate of conversion of roundwood to timber products. recurved
Curved backwards. reflexed
Bent sharply backwards at an angle. reforestation             See also afforestation
Replacing forests after felling. regular (of flowers)
Radially symmetrical, with more than one plane of symmetry; actinomorphic. relative growth rate
At a given instant, the increase in plant material per unit of plant material initially present. Expressed over a period (for example, 1 week) as a mean relative growth rate in g/g/day. Relative growth rate = net assimilation rate x leaf area ratio. relative humidity
The dimensionless ratio of the actual vapour pressure of the air to the saturation vapour pressure, which changes with temperature. reniform
Kidney-shaped. residual herbicide             See also contact herbicide, systemic
A herbicide applied to the soil that remains active for at least several weeks, but sometimes many years. resin
A thick, sticky liquid that comes out of certain trees when cut or damaged and later becomes hard. Acacia senegal produces one of the more valuable resins ('gum arabic') as do Boswellia and Combretum species. resistance
The ability of an organism to exclude or overcome, completely or in some degree, the effect of a pathogen or other damaging factor. reticulate
Marked with a network pattern, usually of veins. rhipidium (of inflorescences)
A cymose inflorescence with branches alternating from one side of the vertical axis to the other; normally flattened in one plane and fan-shaped. rhizobium
Type of bacterium that has the capacity of both invading the roots of certain species of the Leguminosae and fixing atmospheric nitrogen, which is subsequently used by the host plant. rhizome            See also stolon
A horizontal stem growing beneath the soil surface, capable of producing adventitious roots and with nodes having scale leaves subtending axillary buds that may form either rhizome branches or upright shoots. rhizophore
A leaf-bearing root; a leafless stem with roots. ring-barking
A method of killing trees by removing a ring (strip) of bark right down to, and including, the cambium. Usually done near the bottom of the trunk. riparian forest
See gallery forest. river basin
See watershed. riverine
An environment created along permanent and semi-permanent streams because of the increase in soil moisture. This is termed a riverine environment. root
The lower, usually underground, part of a plant. It anchors the plant in the soil and absorbs water and mineral nutrients by means of the root hairs. root climber             See also scrambler, twiner
A plant that raises itself up by means of adventitious roots, which adhere to the plants that support it. root hair
Unicellular, hairlike growth from a root. Functionally important in water and nutrient uptake. root knot nematodes
Sedentary endoparasites; do not kill tissues on the roots but cause swellings or galls to form on the root. root lesion nematodes
Migratory endoparasites; kill many cells as they feed inside the root tissues and cause the formation of dead areas or lesions on the root. root sucker             See also sprout
A shoot arising from an adventitious bud in a root. Some plants, like bananas and date palms, reproduce by sending out root suckers that grow from the mother tree's root system. These can be cut away and planted at another site. Other trees will produce root suckers if their roots are cut some distance from the tree and left exposed (for example, Ocotea usambarensis and Melia volkensii can be propagated in this fashion). rootstock
A root-bearing plant or plant part, generally a stem or root, onto which another plant part (the scion) is grafted. Also, the collective roots in a stand, capable of sprouting. rosette
A group of leaves arising closely together from a short stem, forming a radiating cluster on or near the ground. rotate (of corollas)
Wheel-shaped; with the petals or lobes spreading out from the axis of a flower. roundwood
1. Timber or fuelwood prepared in the round state, that is, from felled trees to material trimmed, barked and cross-cut. Logs, transmission poles, pit props and the like are 'round timber'; with fuelwood included, the term is 'roundwood'.
2. Timber as harvested, before conversion. ruderal
1 (noun) A plant that is associated with human dwellings or agriculture or one that colonises waste ground. Ruderals are often weeds with high demands for nutrients and /or are intolerant of competition.
2. (adj.). Applied to such a plant. rugose
Wrinkled, bearing many ridges. ruminant             See also small animal
An animal that has more than one stomach. The first is called the 'rumen', in which bacterial fermentation takes place and from which the animal is able to regurgitate ingested food back to the mouth for further chewing ('chewing the cud'). Cattle, antelopes, deer, giraffe, sheep and goats are ruminants.

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