B. pustulatum is an unusual species from Malaysia and Borneo - it has thick succulent lip - mmmmm ! 

The flower only opens for a few hours in the morning for a few days .

Bulbophyllum singaporeanum

Despite its name, this plant is not common ( extinct ?) in Singapore. Its current known distribution is Malaysia and  Borneo. Vegetatively, the plant is unique in having very small pseudobulbs and long narrow red-brown leaves. In Southern Malaysia, I have found it growing on the ground scrambling across large boulders and fallen tree but never higher than a few  metres from the ground. The bloom is another stinker - smells like dead fish.

These picture show variations of two plants  of the same species both taken in Peninsula Malaysia - vegetatively they are indistinguishable but the flowers are quite different. The top form appears to be rarer of the two.

In the wild, they occur as a very long vine twining round tree trunks from near ground level upwards, sometimes on very thin branches 

Bulbophyllum macrantum

A rather common lowland species from SE Asia which has hairy pseudobulbs to trap nutrients. The flower is non-resupinate, ie, upside down.

B. patens is a common plant from SE Asia - vegetatively it is like B. macrantum - having upward pointing hairs around the pseudobulbs which help to trap debris to nourish the plant, the leaves however is spade shaped instead of elongated. The upside-down flower is closed in the evening. Unlike most Bulbophyllum, the flower has a sweet fruity smell.