Glossary of Botanical Terms - R

R

raceme

(adjective racemose) an indeterminate inflorescence in which the main axis produces a series of flowers on lateral stalks, the oldest at the base and the youngest at the top; cf. spike.

rachilla (rhachilla)

the axis of a grass spikelet, above the glumes.

rachis

(plural rachises; rachides) the axis of an inflorescence or a pinnate leaf; for example ferns; secondary rachis is the axis of a pinna in a bipinnate leaf distal to and including the lowermost pedicel attachment.

radial

with structures radiating from a central point as spokes on a wheel, for example, the lateral spines of a cactus.

radiate

of daisies, of a capitulum, with ray florets surrounding disc florets.

radical

springing from the root; clustered at base of stem.

radicle

the part of an embryo giving rise to the root system of a plant; cf. plumule.

rainforest

a forest dominated by broad-leaved trees with dense crowns that form a continuous layer (canopy) and with one or more of the following growth forms: epiphytes, lianas, treeferns, palms; eucalypts absent or are present only as isolated emergen, e.g. in Victoria, mesic vegetation is dominated by trees other than eucalypts, often with lianas and epiphytes.

ramet

an individual member of a clone.

ray

1. zygomorphic (ligulate) flowers in a radiate flowerhead, that is, ray-florets/flowers, for example Asteraceae.

2. each of the branches of an umbel.

receptacle

the axis of a flower, in other words, floral axis; torus; for example in Asteraceae, the floral base or common receptacle is the expanded summit of the peduncle on which the flowers are inserted.

recurved

bent or curved backwards or downwards.

reflexed

bent sharply back or down.

registered name

a cultivar name accepted by the relevant International Cultivar Registration Authority.

registered trade mark

a trade mark formally accepted by a statutory trade-mark authority and distinguished by the international ® sign.

registration

1. the act of recording a new cultivar name with an International Cultivar Registration Authority.

2. recording a new cultivar name with a statutory authority like the Plant Breeder’s Rights Office.

3. recording a trade mark with a trade marks office. Compare registered trade mark.

regular

see actinomorphic.

reniform

kidney-shaped.

reticulate

forming a network (or reticulum), e.g. veins that join one another at more than one point.

retrorse

directed backwards or downwards; cf. antrorse.

retuse

with a blunt (obtuse) and slightly notched apex.

revision

an account of a particular plant group, like an abbreviated or simplified monograph. Sometimes confined to the plants of a particular region. Similar to a monograph in clearly distinguishing the taxa and providing a means for their identification; compare monograph.

revolute

rolled under (downwards or backwards), for example when the edges of leaves are rolled under towards the midrib; compare involute.

rhachis

see rachis.

rhizome

a perennial underground stem usually growing horizontally. See also stolon.

rhombic

like a rhombus: an oblique figure with four equal sides; compare trapeziform, trullate.

rhomboid

a four-sided figure with opposite sides parallel but with adjacent sides an unequal length (like an oblique rectangle); see also rhombic.

rhomboidal

a shape, for instance of a leaf, that is roughly diamond-shaped with length equal to width.

root

a unit of a plant's axial system which is usually underground, does not bear leaves, tends to grow downwards, and is typically derived from the radicle of the embryo.

root hairs

outgrowths of the outermost layer of cells just behind the root tips, functioning as water-absorbing organs.

rootstock

short, erect, swollen structure at junction of a plant's root and shoot systems, for example a corm. Also used to describe:

1. a part of a budded or grafted plant which supplies the roots, also called a rootstock, or plants grown specifically to produce these.

2. plants or seeds with some specific attribute, for instance virus-free plants.

rosette

when parts are not whorled or opposite but appear so, due to the contractions of internodes, e.g. the petals in a double rose or a basal cluster of leaves (usually close to the ground) in some plants.

rostrate

with a beak.

rotate

circular and flattened; for example a corolla with a very short tube and spreading lobes (for instance some Solanaceae).

rudimentary

poorly developed and not functional; compare vestigial.

rugose

wrinkled.

rugulose

finely wrinkled.

ruminate

(usually applied to endosperm). irregularly grooved or ridged; appearing chewed. (a common type of endosperm in Myristicaceae).

runcinate

sharply pinnatifid or cleft, the segments directed downward.

runners

see stolon.

rupicolous

rupestral, saxicolous, growing on or among rocks. (compare epilithic, lithophytic)

rush

a plant belonging to the family Juncaceae or, more loosely, applied to various monocotyledons.