Dioecious

Holly (Ilex aquifolium) is dioecious:
(above) shoot with flowers from male plant;
(top right) male flower enlarged, showing stamens
with pollen and reduced sterile stigma;
(below) shoot with flowers from female plant;
(lower right) female flower enlarged, showing stigma
and reduced sterile stamens with no pollen

In botany, where all individuals of a plant species are of a single sex, with male plants which produce only pollen, and female plants which produce only seeds, that species is described as being dioecious (from Greek for "two households").

The converse, with individuals of a plant producing both pollen and seeds, is monoecious (from Greek for "one household").

Some plants are intermediate, with individuals producing mainly pollen but also some seeds, and other individuals producing mainly seeds but also some pollen. These are known as sub-dioecious.

Dioecious plants form a minority of the plant kingdom, but occur in widely scattered plant orders, suggesting that dioecy is the derived condition, with monoecy the condition which plants originally showed. A fair degree of correlation (though far from complete) exists between dioecy and sub-dioecy, and plants that have seeds dispersed by birds (both nuts and berries). It is hypothesized that the concentration of fruit in half of the plants increases dispersal efficiency; female plants can produce a higher density of fruit as they do not expend resources on pollen production, and the dispersal agents need not waste time looking for fruit in male plants.