BBC Gardeners' World

F1 hybrid

The first offspring of a cross between two cultivars, bred under strict conditions to create a uniform, high-yielding crop. Seeds gathered from such hybrids don't breed true.

F2 hybrid

Second generation plants resulting from the self-pollination or interpollination of F1 plants.

Falcate

Usually refers to a leaf that's shaped like the blade of a sickle.

Falls

1) The drooping outer petal of a flower, such as on an iris.

2) Felled timber.

Fan

A method of training plants against a wall or on wires to achieve a fan-like effect.

Farina

A starchy meal that covers flowers, leaves or stems.

Fasciation

When a shoot becomes enlarged and flattened, giving the appearance of several shoots fused together, caused by an abnormality. Often seen on forsythia. The cock's comb ornamental flower is grown specifically for its unusual fasciated flowerheads, which are flattened and crested.

Fasicle

A small or slender bundle, eg, of pine needles.

Fastigiate

A tree or shrub whose branches grow almost vertically.

Feathered

Describes leaves whose veins arise from a single midrib.