Whatever you do, don't throw this Hoya into the briar patch

The way we remember Thomas Hoy, the 2nd Duke of Northumberland's gardener at Syon House, is through 300 species, and some varieties, of mostly waxy leaved creepers.

Hoyas were a novelty in London in the nineteenth century. They grow naturally across southern Asia into the Pacific Islands, with some extending into the Indian region. In Australia there are six native species, all but one extending into other neighbouring countries. 

In this blog in 2009, I was showing off the latest flowers on Wax Plant, Hoya australis. Growing below our decking in Sydney, this climbing vine enjoyed a nice humid and mostly shaded spot, with a little loving attention from time-to-time. The species is a popular plant in cultivation, and easy to grow, but it is just one subspecies of Hoya australis, called subspecies australis. It grows throughout the tropics of Australia and further afield, extending southward into north-eastern New South Wales.

There are four other subspecies: two (sanae, tenuipes) from Cape York Peninsula in Queensland and two from the Top End of Northern Territory, where I was visiting back in October 2016. One of the two Northern Territorian subspecies, oramicola, is found only in the Tiwi Islands, north of Darwin.

The other, rupicola (sometimes considered a separate species, Hoya rupicola) grows throughout monsoonal Northern Territory and in the nearby Kimberley region. I saw it at Litchfield National Park, near Tolmer Falls. 

Both Northern Territory subspecies lack things called colleters, a cluster of glands on the upper surface of the leave near to where the blade connects to its stalk. I gather you will find these in the more commonly cultivated subspecies australis, but I haven't been able to check yet. Thanks to Flickr image by Xylopia they look like this:

Hoya australis subspecies rupicola is a scrambler rather than a climber. In fact often it's little more than a couple of leaves among the rocks, looking as if they'd rather be somewhere else.  The highly succulent (chunky) leaves are good fit for this tough setting and you can see in this picture a stem heading out along the rocks to find another nook for its next cluster of leaves.

The name 'rupicola' means rock loving, or dwelling, and in the original description of this plant (as a species), botanist Ken Hill described rupicola as 'extremely succulent and drought resistant, growing in small humus accumulations usually on sandstone rocks, often in full sun'. Ken reminded us that this region (the monsoonal north of Australia) can have no rain for up to six months of the year.

But the plant is not foolish. In more sheltered places it can bulk up a bit, and one of the best places is scrambling under and around another species, as you can see here. .

*The title is an adaptation of the line used by Br'er Rabbit to escape being eaten by a fox. Brer and our hoya might imply they like the open ground but both thrive amid the undergrowth.