I am trying to find the name of a house plant I have. Each stem has 3 black and purple leaves which fold together and bend down when there is not enough light, as yet there are no flowers, but some small buds on shoots have appeared.

There are MANY different varieties, but I believe you are talking about a prayer plant.

Sounds to me like you are describing the Oxalis regnellii atropurpurea or, Purple Shamrock plant.

Secretary, Rock Island Horticulture Club