Australian Biological Resources Study
Fern definitions mostly compiled by Mary D.Tindale
(definitions of conifer terms provided by K.D.Hill)
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rachis: a midrib of the lamina, or of a primary, secondary, tertiary etc. pinna. When unqualified, refers to the midrib of the frond, i.e. the main axis above the lowermost primary pinna. Also spelled rhachis. pl. rachises.
radial: applied to a rootstock in which the fronds radiate and the roots are borne on all sides of the organ.
radiospermic: describing radially symmetrical seeds.
ray: of woody stems, a radial band of cells traversing the conducting elements.
receptacle: of ferns, the axis bearing the sporangia and sometimes also paraphyses.
recurved: curved or curled downwards or backwards.
reflexed: bent sharply downwards or backwards.
reniform: kidney-shaped.
reticulum: a network, e.g. of veins. adj. reticulate.
retrorse: bent, and pointing away from the apex. cf. antrorse.
rhizoid: a thread-like unicellular absorbing structure occurring, in the vascular plants, in gametophytes of ferns and some related plants.
rhizome: the creeping (often underground) or climbing stem of a fern.
rhizophore: in Selaginella, a leafless stem that produces roots.
rhomboidal: diamond-shaped or almost so.
rootstock: a swollen root together with the whole or a portion of a very short stem.
rugose: deeply wrinkled.
rugulose: covered with minute wrinkles.