race n. A group or assemblage of organisms that exhibits general similarities but is not sufficiently distinct from other forms to constitute a species (e.g. the three races of avocado (Persea Americana), Mexican, Guatemalan, and West Indian, of which the first is sometimes designated as a separate species, although it hybridizes freely with the other two); sometimes used for individuals of a particular geographical area, in this sense then equivalent to an ecotype (which is not a botanical term).

raceme (L. racemus: bunch, cluster) n. A simple, indeterminate, unbranched, elongated inflorescence with pedicellate flowers upon a common axis maturing from the bottom upwards.

racemiform (L. racemus: bunch, cluster; forma: shape) adj. An inflorescence with the general appearance, but not necessarily the structure, of a true raceme.

racemose (L. racemus: bunch, cluster) adj. An inflorescence whose growing points continue to add to the inflorescence and in which there are no terminal flowers, and the branching is monopodial, as in racemes, or spikes. The term is sometimes used in the same sense as racemiform. Also racemous.

racemose inflorescence A type of flowering shoot (see inflorescence) in which the growing region at the tip of the flower stalk continues to produce new flower buds during growth. As a result, the youngest flowers are at the top and the oldest flowers are at the base of the stalk. In a flattened inflorescence, the youngest flowers are in the centre and the oldest flowers are on the outside. Types of racemose inflorescence include the capitulum, catkin, corymb, raceme, spadix, spike, and umbel. Cf. cymose inflorescence.

racemous See racemose.

racemously adv. See racemose.

racemule (diminutive of L. racemus: bunch, cluster) n. A samll raceme.

racemulose (diminutive of L. racemus: bunch, cluster) adj. Pertaining to or ressembling a racemule; arranged in racemules.

rachial adj. See rachis.

rachides See rachis.

rachidial adj. See rachis.

rachidian adj. See rachis.

rachilla (diminutive of Gr. rakhis: spine) n. A diminutive or secondary axis; a branch of a rachis; the minute axis bearing the individual florets in grass and sedge spikelets; the zigzag center upon which the florets are arranged in the spikelet of grasses or in some sedges; the axis of a grass spikelet, above the glumes. the secondary axes of decompound fern fronds. Also rhachilla.

rachis (Gr. rakhis: spine) n. (pl. rachides or rachises) The central prolongation of the stalk (peduncle), the axis through an inflorescence, or of a leaf stalk (petiole), the axis through a compound leaf. In ferns, the continuation of the stipe through a compound frond, the axis bearing pinnae. Also rhachis.

rachises See rachis.

radial (L. radius: ray, rod, spoke) adj. Arranged or having parts arranged like rays developing uniformly around a central axis, as spokes on a wheel.

radially symmetrical Said of a flower or set of flower parts which can be cut through the center into equal and similar parts along two or more planes; actinomorphic.

radial symmetry The arrangement of parts in an organ or organism such that cutting through the centre of the structure in any direction produces two halves that are mirror images of each other. The stems and roots of plants usually show radial symmetry, while all animals belonging to the Cnidaria (e.g. jellyfish) and Echinodermata (e.g. starfish) are radially symmetrical - and typically sessile - in their adult form. The term actinomorphy is used to describe radial symmetry in flowers (e.g. a buttercup flower). Cf. bilateral symmetry.

radiant See radiate.

radiate (L. radiatus: with rays, beams) adj. With parts spreading from a central point; in the Compositae (Asteraceae), with some of the flowers of the involucrate head ligulate (the petals united into a strap-like corolla). Also radiant.

radiation (L. radiatio: influence, radiance) n. Event of rapid cladogenesis, believed to occur under conditions where a new feature permits a lineage to move into a new niche or new habitat, and is then called an adaptive radiation.

radical (L. radix, radicis: root) adj. Pertaining to the root; arising from, or near, the roots. Of leaves, clustered at the base of the stem.

radicant (L. radix, radicis: root) adj. Rooting from the node of a prostrate stem or from a leaf, as ivy.

radicel (L. radicula: small root) n. A minute root, a rootlet.

radicicolous (L. radix, radicis: root; colere: to inhabit) adj. With the flower positioned directly upon the root crown.

radicle (L. radicula: small root) n. The part of a plant embryo that develops into the root system; the tip of the radicle is protected by a root cap and points towards the micropyle; on germination it breaks through the testa and grows down into the soil. Rootlet springing from the sides and base of the stem. Archaic term for rhizoid.

radiculose (L. radicula: small root) adj. Having many rootlets; covered with rhizoids.

radiospermic (L. radius: spoke, beam, ray; Gr. sperma: seed) adj. Having seeds which are round or ovoid. Contrast with platyspermic.

ramal See rameal.

ramble v. To extend or grow at random.

rameal (L. ramus, branch) adj. Pertaining to the branches.

ramenta See ramentum.

ramentaceous (L. ramentum: shavings, turnings) adj. Having ramentum; ressembling or vovered with ramenta.

ramentum (L. ramentum: shavings, turnings) n. (pl. ramenta) The flattened, scaly outgrowths on the epidermis of the stem and leaves of some ferns.

ramet (L. ramus: branch) n. An individual member of a clone.

ramification (L. ramus: branch) n. The arrangement of branching parts; a structue formed of branches.

ramiflorous adj. Bearing flowers directly from branches and leafless twigs, (but not on the trunk).

ramiform (L. ramus: branch; forma: shape) adj. Branch-like in form; branched.

ramose (L. ramus: branch) adj. With many branches; branching.

ramosely adv. See ramose.

ramosity n. See ramose.

ramous (L. ramosus: branchy) adj. Ramose; ressembling or pertaining to branches.

ramuli See ramulus.

ramulose (L. ramulosus: with branchlets) adj. Having many small branches. Also ramulous.

ramulous See ramulose.

ramulus n. (pl. ramuli) Branchlet, smallest division of much-branched plant.

ramus (L. ramus: branch) n. A branch, as of a plant, vein, etc.

range n. The area of distribution of aplant.

rank n. In traditional taxonomy, taxa are ranked according to their level of inclusiveness. Thus a genus contains one or more species, a family includes one or more genera, and so on. A vertical row, as of leaves. When you sight along the length of a branch from the tip end, if it appears there are two rows of leaves, either opposite or alternate, the branch is 2-ranked; if three rows, it is 3-ranked, etc.

ranked adj. With the foliage arranged in longitudinal planes around the stem; arranged into vertical rows; e.g. the leaf arrangement in leafy liverworts or the moss Orthostichidium.

raphae See raphe.

raphe (Gr. raphź: seam) n. (pl. raphae) The part of the stalk of an anatropous ovule that is fused along the side of the ovule. A ridge on the seed formed by the portion of the funiculus fused to the seed coat. A ridge on a seed marking the line of fusion between an anatropous (inverted) ovule and the funicle. Any other groove, ridge, or suture line marking the line of fusion between two originally separate structures. Also rhaphe.

raphide See raphides.

raphides (Gr. raphis, raphidos: needle) n. pl. Needle-shaped crystals of calcium carbonate or calcium oxalate found in specialized plant cells called idioblasts. It is believed that the raphides are a defense mechanism against plant predators, as they are likely to tear the soft tissues of the throat or esophagus of a plant predator chewing on the plant's.

rapiformis (L. rpum: turnip; forma: shape) adj. Turnip-shaped.

rash n. A skin eruption.

ratoon n. A shoot arising from the root of a plant that has been cut down, especially a sugar cane after it has been cropped..

Raunkiaer's Classification System The Danish botanist Raunkiaer noted that the traditional classification of plants into trees, shrubs, herbs, and other categories based on habit does not take into account much of the ecology or lifestyle of the plants. He devised an alternative system, based on lifestyle and the position of buds (the points on a stem from which new shoots grow in the spring), with the following categories: phanerophyte, chamaephyte, geophyte, therophyte, liana, hemi-epiphyte, epiphyte, errant vascular hydrophyte, vascular semi-parasite and vascular parasite.

ray n. Of a compound umbel, one of the first (lower) series of branches of the inflorescence axis. The strap-like portion of a ligulate flower (or the ligulate flower itself) in the Compositae (Asteraceae).

ray floret See ray flower.

ray flower The bilaterally symmetrical flowers around the edge of the head in many members of the Compositae (Asteraceae); each ray flower resembles a single petal. Also ray floret. Cf. disk floret.

ray initials Initials of the vascular cambium that produce ray cells.

rbcL A gene which is located in the chloroplast of photosynthetic organisms. It codes for the large subunit of the protein rubisco, and its sequence has been useful in plant phylogenies.

recalcitrant adj. Said of germination, the seed needing to remain hydrated if germination is to occur.

recalcitrant seed A seed that does not survive drying and freezing. 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.

recapitulation theory See biogenetic law

recaulescent adj. Said of axillary branching, when the bud as it were shifted onto the subtending leaf, forming a 'stalk' on which bud and leaf are borne.

receptacle (L. receptaculum: store, refuge) n. The tip (distal end) of a flower stalk, usually more or less enlarged, flattened, or cup-like, on which the petals, sepals, stamens, and carpels are borne; the way the receptacle develops determines the position of the flower parts; it can be dilated and dome-shaped, saucer-shaped, or hollow and enclosing the gynoecium (see epigyny, hypogyny, perigyny); in some plants it may become part of the fruit (see pseudocarp). In ferns, an axis on which sporangia arise. A swollen part of the thallus of some algae, e.g. Fucus, that bears the conceptacles in which the sex organs are situated. In bryophytes, a disc or wart-like mass of tissue bearing antheridia or archegonia and found directly on the thallus (e.g. Conocephalum, Corsinia), inside the thallus (e.g. Pellia), or elevated and terminating a gametangiophore (e.g. Marchantia).

receptacular (L. receptaculum: store, refuge) adj. Carried on the receptacle; pertaining to the receptacle.

recessive (L. recessus: regressed, fallen back) adj. Qualifies the allele that is not expressed in the phenotype when two different alleles are present in the cells of an organism. The aspect of a characteristic controlled by a recessive allele only appears when two such alleles are present, i.e. in the double recessive condition. Cf. dominant.

reciprocal crosses Crosses in which the sources of male and female gametes are reversed.

reclinate (L. reclinatus: leaned back) adj. Bent abruptly downward; curved backwards.

reclining (L. reclinis: leaned back) adj. With the lower portion somewhat flattened along the ground but the upper parts curving upward; bending or curving downward; lying upon something and being supported by it.

recombination n. The observed new combinations of characters different from those exhibited by the parents; percentage of recombinations equals percentage of crossing-over only when the genes are relatively close together; cytological crossing-over refers to the process, whereas recombination or genetic crossing-over refers to the observed genetic result.

recumbence n. See recumbent.

recumbency n. See recumbent.

recumbent (L. recumbere: to lie [back]) adj. Leaning or resting on the ground, or upon anything; prostrate.

recumbently adv. See recumbent.

recurrent parent The parent to which successive backcrosses are made in backcross breeding.

recurrent selection A method of breeding designed to concentrate favorable genes scattered among a number of individuals by selecting in each generation among the progeny produced by matings inter se of the selected individuals (or their selfed progeny) of the previous generation.

recurve v. See recurved.

recurved (L. recurvus: curved, bent) adj. Curved or curled downwards (abaxially) or backwards (inward); in leaves, referring to margins, apices, or marginal teeth; in peristome, referring to teeth curved outward and more or less downward. Syn. retrocurved. Cf. incurved.

recurving See recurved.

red algae See Rhodophyta.

red bed See red beds

red beds Sedimentary rocks, generally sandstones, which are red due to their grains being coated with hematite.

reduced (L. reducere: to bring back) adj. Diminished in size; simplified during evolution; e.g. the peristome of Leptostomum; not fully developed; e.g. the smaller leaves at base of a stem.

reduction division See meiosis.

reduplicate adj. Valvate with the edges reflexed, folded back, so as to project outward. Also reduplicative.

reduplicative See reduplicate.

reduplicatively adv. See reduplicative.

reflexed (L. reflexus: bent backward) adj. Bent sharply downwards (abaxially) or backwards (inward), generally referring to leaf margins or leaves on a stem; abruptly reclinate. Syn. retroflexed. Cf. inflexed.

refoliate (L. re-: again; folia: leaf) v. To produce leaves again, as after rain, wind, or disease.

refracted (L. refractus: broken) adj. Bent backward from the base.

refrigerant adj., n. Reducing fever. An agent used to reduce fever.

registered seed A class of certified seed that is the progeny of breeder or foundation seed and is produced and handled under procedures established by the certifying agency for the purpose of maintaining genetic purity and identity.

regma (Gr. rźgma, rźgmatos: breaking, tearing) n. (pl. regmata) A dry fruit that is characteristic of the geranium family. It is similar to the carcerulus but breaks up into one-seeded parts, each of which splits open to release a seed. A dry fruit of three or more carpels which separate at maturity. A type of schizocarp.

regmata See regma.

regular (L. regularis: used as a rule) adj. Radially symmetrical; said of a flower in which all parts are similar in size and arrangement on the receptacle. Syn. isanthous. Cf. irregular. See actinomorphic.

regular flower Generally symmetrical and uniform in the number of its parts.

relatedness (L. relatus: carried back) n. Two clades are more closely related when they share a more recent common ancestor between them than they do with any other clade.

relict (L. relictus: left behind) adj, n. A plant which has survived from an earlier flora or from a past geologic epoch. Something that has survived; a remnant. A group of animals or plants that exists as a remnant of a formerly widely distributed group in an environment different from that in which it originated.

relictual adj. Of something that has survived. Of a relict.

remote (L. remotus: distant) adj. Distantly spaced, widely separated; e.g. the leaves along a stem.

reniform (L. renes: kidney; forma: shape) adj. Having the form or shape of a kidney; having the form of an oval with the ends curved around in the same direction.

repand (L. repandus: arched) adj. With a slightly wavy or weakly sinuate margin; undulate.

repandate (L. repandus: arched) adj. Undulate, but less evenly so.

repent (L. repens, repentis: crawling) adj. Said of a stem that is prostrate, creeping, rooting at the nodes, especially whwn growing along the ground or just under the surface. Syn. reptant.

replum (L. replum: chassis) n. Partition or septum between the two valves or compartments of silicles or siliques in the Cruciferae (Brassicaceae). A longitudinal partition in an ovary, formed between parietal placentas. The hardened framework of the placenta which remains when the outer walls or valves of a silique fall away; the septum which holds the seeds.

reptant (L. reptare: to crawl) See repent.

resin (L. resina: resin) n. A naturally occurring acidic polymer secreted by many trees (especially conifers) into ducts or canals. Resins are found either as brittle glassy substances or dissolved in essential oils. Their functions are probably similar to those of gums and mucilages, i.e. protective.

resiniferous (L. resina: resin; ferre: to carry) adj. Yielding resin.

resinoid adj.; n. Relating to, resembling, or containing resin. A synthetic resin, especially a thermosetting resin.

resinous (L. resina: resin) adj. Bearing resin and often, therefore, sticky; of the nature of or resembling resin; pertaining to or characteristic of resin; full of or containing resin.

resorbed adj. See resorption.

resorption n. The disappearance or erosion of parts of cell walls (resorbed); e.g. Sphagnum leaves.

restorer line An inbred line that, when crossed on a male-sterile inbred, causes the resulting hybrid to be male fertile.

Restriction Fragment Length Polymorphism Restriction Fragment Length Polymorphism (RFLP) is a technique in which organisms may be differentiated by analysis of patterns derived from cleavage of their DNA. If two organisms differ in the distance between sites of cleavage of a particular restriction endonuclease, the length of the fragments produced will differ when the DNA is digested with a restriction enzyme. The similarity of the patterns generated can be used to differentiate species (and even strains) from one another.

resupinate (L. resupinatus: bent backward, turned back) adj. Upside down due to twisting of the pedicel through 180°, as the flowers of most Orchidaceae; inverted; appearing as if upside down; bent backwards or reversed by the twisting of the stalk. Also resupine.

resupination (L. resupinatus: bent backward, turned back) n. A resupinate condition.

resupine (L. resupinatus: bent backward, turned back) adj. Lying on the back; supine. Refers to a flower or leaf on which the stalk twists a full half turn, 180 degrees, so that the organ appears to be upside down. Also resupinate.

reticula See reticulum.

reticulate (L. reticulatus: made as a network, latticed) adj. Interconnecting, like a network, netveined; especially: having veins, fibers, or lines crossing.

reticulation (L. reticulatus: made as a network, latticed) n. The entire network of reticulate veins, ribs, coloring or fibers. A reticulated formation. Joining of separate lineages on a phylogenetic tree, generally through hybridization or through lateral gene transfer. Fairly common in certain land plant clades; reticulation is thought to be rare among metazoans.

reticulodromous adj. Said of leaf venation, pinnate venation (camptodromous in particular), in which the secondary veins lose their identities towards the margin as they branch repeatedly.

reticulum (L. reticulum: net) n. (pl. reticula) A network of veins or fibers. Syn. reticulation.

retinacula See retinaculum.

retinaculum (L. retinaculum: any type of bond) n. (pl. retinacula) A band or band-like structure that holds an organ in place; a hook-like structure to which another structure is tethered; in Orchidaceae and Asclepiadaceae, the structure (sticky gland) to which pollen masses (the pollinia) are attached; in Acanthaceae, the persistent stalk of an ovule, i.e. the hook-like funicle of a seed.

retinol See vitamin A.

retrocurved (L. retro: backward, back, behind; curvus: curved) See recurved.

retroflexed (L. retro: backward, back, behind; flexus: curve) See reflexed.

retrorse (L. retro, backwards; versus, past participle of vertere, to turn) adj. Having hairs or other processes turned toward the base; directed backward or downward. Cf. antrorse.

retuse (L. retusus: blunt, obtuse) adj. With a shallow notch in a round or blunt apex; having a broad end with a central depression.

reverse osmosis The process in which pure water is produced by forcing waste or saline water through a semipermeable membrane.

revoluble adj. Rolling away, referring to an annulus that falls in a broken ring.

revolute (L. revolvere, to roll back) adj. Said of margins that are rolled backwards (towards the underside, i.e. the abaxial side), or rolled downwards (e.g. Ledum gorenlandicum); having a rolled-back edge. Cf. involute.

rexigenous adj. Said of an intercellular space caused by the rupture of the cells there.

RFLP See Restriction Fragment Length Polymorphism.

rhabdocarpous (Gr. rabdos: stick; karpos: fruit) adj. With long rod-shaped fruits.

rhachilla See rachila.

rhachis See rachis.

rhaphe See raphe.

rheogameon n. A species composed of segments with marked morphological divergence but gene exchange takes place between them; contiguous segments are interfertile; apomixis is not present.

rheophilous adj. Thriving in running water, dwelling in flowing creeks.

rheophyte n. A narrow-leaves plant, usually a shrub, growing in or by rivers and periodically subject to immersion in fast-flowing waters.

rheumatism n. 1. Any of several pathological conditions of the muscles, tendons, joints, bones, or nerves, characterized by discomfort and disability. 2. Rheumatoid arthritis.

rhipidia See rhipidium.

rhipidium (Gr. ripis. ripidos: fan) n. (pl. rhipidia) A flattened, fan-shaped cyme. An inflorescence of cymose units, the lateral branches developed alternately in opposite directions.

rhizanthous (Gr. riza: root; anthos: flower) adj. With the flowers arising so close to the ground that they appear to be arising from the root.

rhizautoicous adj. With with the androecium on a very short branch attached to the female stem by rhizoids and appearing to be a separate plant. Cf. autoicous.

rhizine n. (pl. rhizines, rhizinae) An extension of the lower cortex, which serves to attach a foliose thallus to its substrate; may be of various lengths, thicknesses, colors and degrees of branching. Strands of hyphae found on the lower surface of many foliose lichens.

rhizobia See rhizobium.

rhizobium n. (pl. rhizobia) The common name given to a group of small, rod shaped bacteria of the genus Rhizobium, which have the ability to produce nodules on the roots (or, in some cases, the stems) of leguminous plants, such as clover and beans, resulting in nitrogen fixation.

rhizocarpic (Gr. riza: root; karpos: fruit) adj. With the roots living for several to many years and the stems dying each year. as perennial herbs. Also rhizocarpic.

rhizocarpous See rhizocarpic.

rhizogenic (Gr. riza: root; gennaō: to produce) adj. Root producing.

rhizohyphae n. Organs of attachment, consisting of clustered hyphae, developing from the lower medulla, usually black, bluish or whitish (especially in Pannariaceae).

rhizoid (Gr. riza: root; eidō: to look like) n. Root-like cells in charophytes. A thread-like, unicellular absorbing structure, occurring in fern gametophytes and in some non-vascular plants, mosses, etc., which usually aids in anchoring and to increase surface area for acquiring water or nutrients; i.e. a root-like structure lacking conductive tissues (xylem and phloem). In liverworts and hornworts rhizoids are one-celled and usually hyaline; in mosses rhizoids are usually brown to reddish, simple or branched, multicellular filaments, generally with oblique end-walls. Cf. tomentum,

rhizoidal adj. See rhizoid.

rhizomatous (Gr. riza: root) adj. Rhizome-like; with rhizomes.

rhizomatous tuber Same as a corm.

rhizome (Gr. riza: root) n. A subterranean, usually horizontal, somewhat elongate, root-like stem, such as found in many ferns, sending out leaves and shoots from its upper surface and roots from its lower surface; it is often thickened by deposits of reserve food material, and is distinguished from a true root in possessing buds, nodes, and usually scalelike leaves; it enables the plant to survive from one growing season to the next and in some species it also serves to propagate the plant vegetatively; it may be thin and wiry, as in couch grass, or fleshy and swollen, as in Iris. Sphenophytes spread via rhizomes, but also produce erect stems. Any prostrate or subterranean stem, usually rooting at the nodes and becoming erect at the apex. Compact upright underground stems, as in rhubarb, strawberry, and primrose, are often called rootstocks. Also rootstalk.

rhizome chaff Small pieces of rhizomes which are spread upon the ground and covered with soil so they can take root and form new plants.

rhizomorph n. A rootlike structure of certain fungi, such as the honey fungus Armillaria mellea, consisting of a dense mass of hyphae.

rhizomorphous (Gr. riza: root; morphź: shape) adj. Root-like in appearance.

rhizophyllous (Gr. riza: root; phyllon, leaf) adj. With roots arising from the leaves.

Rhizopoda (Gr. riza: root; pous, podos: foot) n. A phylum of the Protoctista that contains the amoebas and cellular slime moulds. They are characterized by the possession of pseudopodia, which are used for locomotion and engulfing food particles. Rhizopods are found in freshwater and marine habitats and the soil. The amoebas reproduce by binary fission, whereas the cellular slime moulds aggregate into a slimy mass that produces spores. See also Amoeba; protozoa.

rhizopodial adj. Of a type of morphological organisation forming amoeboid cells which lack a rigid cell wall.

rhizosphere n. The soil zone that surrounds and is influenced by the roots of plants.

rhizotaxis See rhizotaxy.

rhizotaxy (Gr. riza: root; taxis: arrangement) n. The type of arrangement of roots on a plant. Also rhizotaxis.

Rhodophyta (Gr. rodon: rose; phyton: plant) n. A phylum of algae that are often pink or red in colour due to the presence of the pigments phycocyanin and phycoerythrin. Members of the Rhodophyta may be unicellular or multicellular; the latter form branched flattened thalli or filaments. They are commonly found along the coasts of tropical areas.

rhombic (L. rhombus: lozenge, rhombus) adj. With four nearly equal sides, but unequal angles, diamond shaped. Resembling a rhombus, an equilateral parallelogram. Also rhombical.

rhombical See rhombic.

rhomboid (Gr. rhombos: lozenge, rhombus; eidō: to look like) adj. Said of leaves, tepals, etc. which are diamond shaped, with the base and tip having acute angles and the sides having obtuse angles. Also rhomboidal.

rhomboidal (Gr. rhombos: lozenge, rhombus; eidō: to look like) adj. Quadrangular, nearly rhombic, with obtuse lateral angles.

rhytidome n. The cork cambium and the tissues it isolates, since such cambia are often formed successively deeper and deeper in the stem, there may be pockets of cortical or phloem tissue in with the cork.

rib n. A main longitudinal vein in a structure, particularly if raised above the surrounding surface, as in some leaves and other organ. A ridge of plant-tissue thicker than its surrounding

ribbed adj. With prominent ribs or veins.

ribose n. A sugar.

ribosomal adj Related to the ribosomes.

ribosomal DNA Chromosomal or (in the case of rDNA amplification) extrachromosomal DNA which codes for ribosomal RNA.

ribosome n. A granular particle present in enormous numbers in the cytoplasm of nearly all cells, either free or bound to the surface of membranes with the cell. Ribosomes are composed of RNA and protein and are the site of protein synthesis. During synthesis they often link together in a chain (polyribosome or polysome).

rictus n. The mouth of a bilabiate corolla.

ridge n. The long and narrow upper edge, angle or crest of something. An elongate crest or a linear series of crests.

ridged adj. With angular, with lengthwise lines.

rigescence n. See rigescent.

rigescent (L. rigescere: to stiffen, to harden) adj. Becoming numb or stiff, becoming rigid.

rigid (L. rigidus: stiff, hard) adj. Stiff and inflexible.

rim n. A projecting edge or flange.

rimose (L. rimosus: cracked, fissured) adj. With fissures, chinks or cracks, as in the bark of somme trees. Also rimous.

rimous See rimose.

rind n. A thick outer covering, as in citrus, etc.

ring porous Said of wood, with vessels in more or less distinct rings, usually at the beginning of the season's growth.

ringent (L. ringor, ringi: to growl showing teeth) adj. Gaping; with widely spreading lips, as in some corollas.

ringworm n. Any of a number of contagious skin diseases caused by several related fungi, characterized by ring-shaped, scaly, itching patches on the skin and generally classified by its location on the body. Also called tinea.

riparian (L. riparius: that frequents banks or shores) adj. Growing in streams, springs, or seeps; of, or relating to, rivers or streams. Also riparious.

riparious See riparian.

ripe adj. Fully developed and mature.

rivulose (L. rivulus: small brook) adj. With meandering channels or marked with sinuous lines resembling a rivulet

RNA 'ribonucleic acid'. The nucleic acid which carries the DNA message into parts of the cell where it is interpreted and used. The 18S ribosomal RNA sequence has been used in many groups of organisms to reconstruct phylogeny.

rockery n. Garden on rocky ground or among rocks, for the growing of alpine or other plants. A garden decorated with rocks, usually a wide variety of interestingly shaped, multicolored rocks, esp. quartz. Also rock garden.

rock garden See rockery.

rogue n. A variation from the standard type of a variety or strain.

roguing n. The removal of undesirable individuals to purify the stock.

root n. The part of a plant, usually below the ground, that holds the plant in position, draws water and nutrients from the soil, stores food, and is typically non-green and derived from the radicle of the embryo.

rootlet n. A radicel; a little root or small branch of a root.

root cap A group of cells that covers the apical meristem of the root.

root hair A projection from an epidermal cell of the root.

root nodule A swelling on the roots of certain plants, especially those of the family Fabaceae (Leguminosae), that contains bacteria (notablyRhizobium) capable of fixing atmospheric nitrogen into ammonia, which is subsequently converted to nitrates and amino acids (see nitrogen fixation). Plants that possess root nodules increase soil fertility by increasing the nitrate content of the soil. The practice of crop rotation will normally include the cultivation of a leguminous species.

root pressure Pressure in the roots which, when the shoot is cut off, will cause liquid to secrete from the root stump; the mechanisms and tissues involved in this process are not clearly understood.

rootstalk n. See rhizome.

rootstock n. A short, erect, swollen structure at the junction of the root and shoot systems of a plant. A rhizome. The root system and lower portion of a woody plant to which a graft of a more desirable plant is attached by a graft.

root tuber Swollen food-storing roots.

roridulate (L. roridus: dew covered) adj. With a covering of waxy platelets, appearing moist, dewy. Also roridulous.

roridulous See roridulate.

roseate (L. roseus: oink) adj. Rose-colored; rosy; tinged with red.

rose hip See rose-hip.

rose-hip n. The aggregate fruit of the rose plant, consisting of several dry fruitlets enclosed by the enlarged, fleshy, usually red floral cup that is used for jelly or tea. Also hip.

rosette n. A group of organs, such as leaves, clustered and crowned around a common point of attachment, usually the base of the stem, just above the ground. A dense radiating cluster of leaves (or other organs), usually at or near ground level.

rosette leaves The leaves at the base of the stem when these are more or less flat on the ground and form a circle.

rosoid adj. Said of a leaf tooth in which the central vein terminates subapically and there is a large clear glandular foramen, two straight higher-order secondary veins also terminate in the foramen.

rostella See rostellum

rostellate (L. rostellum: small beak) adj. With a tiny, short, stout, terminal beak.

rostellum (L. rostellum: small beak) n. (plural rostella) A beak-like upward extension of the stigma in Orchidaceae. A small beak.

rostra See rostrum.

rostrate (L. rostratus: curved with a beak shape) adj. Having a beak; with a short, stout, terminal beak; describing an operculum with a long beak.

rostrum (L. rostrum: beak) n. (pl. rostra or rostrums) A beak-like structure.

rosular See rosulate.

rosulate (L. rosula: little rose) adj. Clustered into a rosette; with the leaves arranged in basal rosettes, the stem very short or lacking; e.g., with the habit of small apparently acaulescent plants in which basal bracts grade continuously into about six, more or less uniform, broad spreading, vegetative leaves. Also rosular.

rotate (L. rota: wheel) adj. Shaped like a wheel; radially spreading in one plane; circular and flattened, e.g. of a corolla with a very short tube and spreading lobes; applied especially to a gamopetalous short tube corolla with a spreading limb.

rotifer n. Any of various minute multicellular aquatic organisms of the phylum Rotifera, having at the anterior end a wheellike ring of cilia.

Rotifera n. Phylum of predominantly free-living, microscopic, aquatic or semiterrestrial pseudocoelomates. Each rotifer has a head bearing a crown of cilia, the corona, at the anterior end; most rotifers feed with the aid of currents generated by the coronal cilia. A posterior foot, often equipped with two or three toes, contains adhesive glands permitting temporary attachment to objects. Unique grinding jaws are found in the pharynx, and an esophagus, stomach, and intestine can be distinguished. The excretory system consists of ciliated cells, called flame cells, that move collected liquids into two coiled tubes called protonephridia; these tubes open into a contractile bladder. The reproductive system is simple, consisting in the female of ovary, yolk gland, and oviduct, and in the male of testis and sperm duct. The intestine, bladder, and reproductive ducts unite to form a cloaca. Rotifers, of which there are about 1,500 known species, are widely distributed in freshwater and marine habitats; they also live in the soil, in mosses, and associated with lichens on rocks and trees. A few are parasitic. Most feed on bacteria, algal cells, small protozoans, or organic detritus. As a rule, only female rotifers are seen; in some species the males have never been observed. Diploid eggs develop parthenogenetically, i.e., without fertilization, to produce females. Under some conditions, haploid eggs are produced; these develop parthenogenetically into males or can be fertilized, developing into dormant female embryos with heavy shells (resting eggs). Many species can survive in a dry form for long periods of time, emerging from a dormant state and becoming active when moisture is available.

Rotliegende n. The Lower Permian red beds underlying the Zechstein. Although old, the word is still very much in use, notably in the oil industry, since much of northern Europe's natural gas is obtained from this rock unit.

rotund (L. rotundus: round) adj. Round or rounded in outline.

rotundate (L. rotundus: round) adj. Rounded; imperfectly orbicular; in the form of, or terminated by, an arc.

rotundifolious (L. rotundus: round; folia: leaf) adj. With round leaves. Also rotundifolius.

rotundifolius See rotundifolious.

roundworm n. Any worm of the class Nematoda, including Ancylostoma duodenale, Ascaris lumbricoides, Enterobius vermicularis, and Strongyloides stercoralis, that may infect the gastrointestinal tract of humans.

route I A kind of iridoid, derived from deoxyloganicacid, the normal route I iridoid not undergoing oxidation.

route II A kind of iridoid derived from epi-deoxyloganicacid.

rubefacient adj., n. Producing redness, as of the skin. A substance that irritates the skin, causing redness.

rubescent (L. rubere: to blush) adj. Becoming red or reddish.

rubiginose See rubiginous.

rubiginous (L. rubiginosus: rusty) adj. Rust-colored; brownish-red. Also rubiginose.

rubisco n. A protein which fixes carbon in photosynthetic organisms. It binds molecules of carbon dioxide to a five-carbon molcule. Rubisco is the most common protein on earth.

ruderal (L. rudus, ruderis: rubbles, debris) adj. Growing in disturbed habitats, along roadsidses, among rubbish; weedy.

rudiment n. An imperfectly developed organ, a vestige.

rudimentary (L. rudimentum: beginnings, trials) adj. Poorly developed and not functional. Cf. vestigial, obsolete, reduced.

rufescent (L. rufus: reddish, red) adj. Somewhat reddish; becoming reddish; tinged with red; rufous.

rufous (L. rufus: reddish, red) adj. Reddish-brown. Also rufescent.

rugose (L. ruga: wrinkle) adj. Having or full of wrinkles; corrugated; ridged; applied to leaves in which the reticulate venation is very prominent beneath, with corresponding creases on the upper side; e.g. the leaves of Neckera.

rugulose (diminutive of L. ruga: wrinkle) adj. Covered with minute wrinkles; finely rugose.

ruminate adj. Mottled in appearance, e.g. of bark, or of the food reserves in a seed. Roughly wrinkled, as if chewed.

runcinate (L. runcina: plane [as a tool]) adj. Pinnatified, with the lobes convex before and straight behind, pointing backward, like the teeth of a saw, as in the dandelion leaf; deeply lobed and with the lobes slanted away from the apex. Sharply pinnatifid or cleft, the segments directed downward. In the form of overlapping arrowheads, the backwards-facing barbs usually curved; saw-toothed, with lobes pointing towards the base.

runner n. A specialized stolon consisting of a prostrate stem rooting at the node and forming a new plant which eventually becomes detached from the parent plant as in a strawberry plant. A prostrate branch that roots at its joints.

rupestral adj. Growing on rock or rock walls. Cf. saxicolous.

ruptile (L. ruptus: broken) adj. Dehiscing irregularly.

rush n. (pl. rushes) Any of various monocotyledonous, grass-like, often tufted marsh plants of the family Juncaceae, having cylindrical often hollow stems.

rush-like adj. Grass-like in appearance, with inconspicuous flowers.

rust n. A minute mold or fungus forming reddish or rusty spots on the leaves and stems of cereal and other grasses, now usually believed to be a form or condition of the corn mildew. As rust, it has solitary reddish spores; as corn mildew, the spores are double and blackish. Rust is also applied to many other minute fungi which infest vegetation.

rutin n. A glucoside resembling, but distinct from, quercitrin. Rutin is found in the leaves of the rue (Ruta graveolens) and other plants, and obtained as a bitter yellow crystalline substance which yields quercitin on decomposition.