Staminode
In botany, a staminode is an, often rudimentary, sterile or abortive stamen. This means that is does not produce pollen. Staminodes are frequently inconspicuous and stamen-like, usually occurring at the inner whorl of the flower.
showing a hairy yellow staminode
Sometimes, the staminodes are modified to produce nectar, such as in the Witch hazel (Hamamelis).
Staminodes can be a critical characteristic for differentiating between species, such as in the orchid genus Paphiopedilum.