twoleaved

Twoleaved is an adjective used in botany and horticulture to describe a plant condition in which only two leaves are present at a given node or in a given context. In practice, it most often refers to a bifoliate arrangement, where two leaves arise opposite each other on the stem, forming a pair. The term can also describe the seedling stage of dicotyledonous plants, in which the embryo has two cotyledons, or seed leaves, before true leaves develop.

Origin and usage: The form “twoleaved” is a straightforward compound of two and leaved. It occurs chiefly in older botanical writings and in some horticultural glossaries. In modern terminology, the simpler expressions bifoliate, difoliate, or opposite-leaved are more common.

Notes on interpretation: Two-leaved can describe a steady state with two leaves per node (opposite phyllotaxy) or the seed stage with two cotyledons. It is distinct from terms describing more complex leaf forms such as trifoliate (three-leaved) or palmatifoliate. It is not a taxonomic rank or a genus name, but a descriptive character used in keys, descriptions, and horticultural notes.

See also: leaf arrangement, phyllotaxy, bifoliate, opposite leaves, dicotyledon.