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Illegitimate seed: Resulting from natural cross-pollination between plants or clones where the male parent cannot be ascertained.

Imbricate: Overlapping like tiles; in a flower bud when one sepal or petal is wholly external and one wholly internal and the others overlapping at the edges only.

Imparipinnate: Pinnate with an odd terminal leaftet. 

Inbred line: The product of inbreeding; a line originating by self-pollination and selection.

Incised: Cut rather deeply.

Incompatibility: Failure to obtain fertilization and seed formation after self-pollination, or within or between clones.

Indefinite: Numerous, as of stamens.

Indehiscent: Not opening when ripe.

Indeterminate: An inflorescence in which the terminal flowers are the last to open, so that the floral axis may be prolonged indefinitely by a terminal bud.

Indigenous: Native to a particular area or region.

Indumentum: A covering, as of hairs, scales, etc.

Induplicate: Margins folded or rolled inwards.

Indurated: Hardened and toughened.

Inferior: Beneath, lower, below; an inferior ovary is one which is below the calyx leaves.

Inflorescence: The arrangement and mode of development of the flowers on the floral axis.

Integument: The covering of an organ; the outer envelope of an ovule.

Internode: The portion of the stern between two nodes.

Interpetiolar: Of stipules placed between the petioles of opposite leaves.

Intrapetiolar: Between the petiole and the stem.

Introrse: Of anthers whose line of dehiscence faces towards the centre of the flower.

Involucre: Whorls of bracts beneath a flower or flower cluster.

Involute: Rolled inwards or towards the upper side.

Irregular flowers: In which parts of the calyx or corolla are dissimilar n size and shape; asymmetric or zygomorphic.

Keeled: Ridged along the middle like the keel of a boat.

Labellum: Lip; the lowest petal of an orchid.

Lacerate: Torn; irregularly cleft or cut.

Lacinate: With narrow parted lobes.

Lactiferous: Containing latex (milky sap).

Lamina: The blade or expanded portion of a leaf or petal.

Lanceolate: Lance-shaped; much longer than broad being widest at the base and tapering to the apex.

Lateral: On or at the side.

Leaflet: One part of a compound leaf.

Legitimate seed: Seed of known or similar parentage.

Lemma: The flowering glume of grasses, being the lower of the two bracts immediately enclosing each floret in the spikelet.

Lenticular: Shaped like a doubly convex lens.

Ligulate: Strap-shaped.

Ligule: A strap-shaped organ or body; the thin membranous projection from the top of the leaf-sheath of grasses.

Limb: The expanded flat part of an organ, particularly in sepals and petals when these are united below.

Line: Used in plant-breeding for a group of individuals from a common ancestry.

Linear: Long and narrow with parallel sides.

Linkage: The relationship between two or more genes in the same chromosome which tend to be inherited together.

Lip: One of the parts of an unequally divided corolla or calyx.

Lobed: Divided, but not into separate leaflets.

Locule: Compartment or cell of an ovary, fruit or anther.

Loculicidal: Splitting down the middle of each cell of the ovary.

Locus, p1. loci: The position of a particular gene on a chromosome.

Lodicules: The scales, usually two in number, at the base of the ovary in grasses, believed to be the rudimentary perianth, which swell to cause the opening of the floret.

Lodged: Fallen or lain down, as cereals beaten down by rain or wind.

Lyrate: Of a leaf with small pinnate lobes below and a larger terminal lobe.