Tree Orchid

This isn't the local largeish white flowered one, but has small yellow flowers. The bulb, leaf, and flower are about 30mm long compared to the 50 to 60mm of the white flowered version.

A Polystachya of some sort?

Originally found on a large Jacaranda tree growing near the 400 Hz power alternator for the universty CDC 170/825 main frame compueters between the Rhodes Chemistry Department and Graham House, which was cut down to make space for the Hamilton Building, housing Computer Science and Information Systems. It was quite a large healthy colony, about the size of an A4 sheet of paper.

Many years ago I transplanted two small sections of the original onto Jacarandas in our garden, and they've done well over the years.

They flower this time of year for a week or two.

Update 2015/11/12:

Here's the other white Polystachia flowering.

The two colonies - the yellow is below left.