Raceme: An unbrached elongated indeterminate inflorescence with pedicelled or stalked flowers opening from the base upwards.
Racemose: Raceme-like inflorescence.
Rachilla (rhachilla): A diminutive or secondary axis, as the stalk of the spikelet in grasses.
Rachis (rhachis): The principal axis of an inflorescence or a compound leaf.
Radical: Of leaves arising at the base o a stem, or from a rhizome.
Radicle: The first root of an embryo or germinating seed.
Raphides: Needle-shaped crystals of mineral substances within plant cells.
Ratoon: New shoots from perennial crops, such as sugar cane after the first crop, used for the production of the second and subsequent crops (ratoon crops).
Ray: The radiating branch of an umbel; the outer floret of an inflorescence of the Compositae with straplike perianth which differs from those in the centre or disc.
Receptacle: The flat, concave or convex part of the stem from which the parts of the flower arise.
Recessive: Of a gene which does not express itself in the presence of the contrasting dominant allele.
Reciprocal crosses: Two crosses between two plants in which the male parent of one cross is the female parent of the second cross.
Recombination: New gene combination as a result of cross-fertilization between individuals differing in genotype.
Recurrent parent: Parent to which hybrid material is crossed in a back-cross.
Recurrent selection: Used in breeding to increase the frequency of favourable genes for yield and other characters by repeated cycles of selection.
Reduction division: In which the chromosomes are reduced from the diploid to the haploid number in meiosis.
Reflexed: Abruptly recurved; bent downwards or backwards.
Regular: Of a radially symmetrical flower; actinomorphic.
Reniform: Kidney-shaped.
Reticulate: Netted, as when the smallest veins of a leaf are connected together.
Retuce: Slightly notched.
Revolute: Of leaves with the margins rolled downwards towards the midrib.
Rhizome: An underground stem which is distinguished from a root by the presence of nodes, buds, and leaves or scales.
Rogue: To weed out inferior or diseased plants, or those which are not true to type.
Rostellum: A small beak; in orchids a projection of the upper edge of the stigma in front of the anthers.
Rotate: Wheel-shaped; of a corolla with a very short tube and lobes spreading out at right angles to the axis.
Ruderal: A plant of waste places.
Rudimentary: Of organs which are imperfectly developed and nonfunctional.
Rugose: Wrinkled.
Ruminate: Of mottled appearance, as in seeds with infolding of darker perisperm into the paler endosperm.
Runcinate: Pinnatifid with the lobes pointing towards the base.
Runner: A slender trailing shoot rooting at the end.
S1, S2 etc: Symbols denoting the first selfed generation, second selfed generation (progeny of the S1) etc.
Saccate: Pouched.
Sagittate: Shaped like an arrowhead; of a leaf base with two acute straight lobes directed downwards.
Samara: An indehiscent winged fruit.
Saprophyte: A plant which derives its food from dead organic matter.
Scabrid, Scabrous: Rough to touch.
Scale: Reduced leaves, usually sessile, thin and dry, and seldom green.
Scandent: Climbing.
Scape: A leaf-less flower-stalk arising from the ground.
Scarious: Thin and dry, not green.
Scion: A detached shoot or bud used in vegetative propagation for grafting or budding.
Seed: The reproductive unit formed from a fertilized ovule, consisting of embryo and seed-coat, and in some cases an endosperm.
Segregation: The separation of homologous chromosomes and genes from different parents at meiosis.
Selection: In breeding, any process, natural or artificial, which permits an increase in the proportion of genotypes of desired characteristics in succeeding generations.
Self-fertile: Capable of fertilization and setting seed after self-pollination.
Self-pollination: Pollination with pollen from the same flower or from other flowers of the same plant.
Self-sterile: Failure to complete fertilization and obtain seed after self-pollination.
Sepal: A member of the outer series of perianth segments, especially when green and foliaceous.
Sepaloid: Sepal-like.
Septate: Divided by one or more partitions.
Septicidal: Dehiscing along the septa of the ovary.
Septum: A partition or cross-wall.
Sericeous: Silky.
Serrate: Toothed like a saw, with regular pointed teeth pointing forwards.
Tilth: Surface soil prepared for planting or cultivation.
Triploid: Having three sets of basic chromosomes (3n).