New Guinean rhododendron a secret no longer

On the weekend I posted a picture of a big, white, vireya rhododendron flower on my Facebook page, dutifully tweeting it and 140 letters of explanation to the Twitterverse. Instagram? Nuh. Snapchat? I forgot about that the day after I joined. So old school social media.

This striking bloom is worth more than a glancing mention on social media. It deserves a ... blog post! Which, through my primitive automated social media marketing, will see it reappear on both Facebook and Twitter (and debut in the more stately rooms of LinkedIn). Still, it's worth a second glance.

The name of this plant is Rhododendron x husteinii. Now. Back in 1989, when Lyn Craven and John Rouse published their paper on its discovery, it was called Rhododendron leucogigas 'Hunstein's Secret'. You can read all about it in the Journal of the American Rhododendron Society, or rely on my potted version below.

Lyn Craven, botanist at Canberra's Australian National Herbarium for more than 30 years, began his scientific career in the plant taxonomy unit of the New Guinea Survey Group of CSIRO. He studied horticulture at Burnley Horticultural College (now part of University of Melbourne) and worked in the Parks and Gardens Branch in Canberra before settling into his position as the Herbarium.

John Rouse was a physicist as well as enthusiastic collector and grower of rhododendrons, publishing over 70 papers on their cultivation and biology. Rhododendron rousei 'John Rouse' seems to have been very much named after him! As a trustee of the Baker Foundation, he was instrumental, along with Director Phil Moors, in setting up our Australian Research Centre for Urban Ecology in 1998. He also sat on the Advisory Committee of the Maud Gibson Trust, another great supporter of the Royal Botanic Gardens Victoria.

His son Andrew Rouse continues in his horticultural footsteps, growing all kinds of rhododendrons in his backyard and small glasshouse in the inner east of suburban Melbourne. Andrew also volunteers at the Rhododendron Garden in Olinda, creating the rhododendron display inside their new glasshouse. The picture above, my social media image, is from his home glasshouse, taken on Saturday (4 June).

Now back to our secretive plant from Mount Hustein. While in Papua New Guinea in August 1966, Lyn Craven found a small seedling 'growing on a branch fallen from the forest canopy' in rainforest at 1200 metres above sea level on Mount Hunstein, in the East Sepik Province. There was only one small individual and enough material for a single cutting. The plant had large leaves but no flowers, and was tentatively assigned to species known from the region, Rhododendron schlechteri.

That cutting was sent to Melbourne where it was successfully propagated, presumably by John Rouse. When it bloomed (illustrated above, from the 1989 journal article), the large white flowers - 12 cm long and 12 cm wide - were more like another species, Rhododendron konori or its presumed cultivar/hybrid Rhododendron 'Gardenia'). However the fine detail of the plant, including the scales on the leaves, shifted its allegiance to a species called Rhododendron leucogigas (a species name very appropriately meaning 'white giant'). known only from the Cycloop Mountains in Irian Jaya.

The Mount Hunstein collection was thought worthy of its own cultivar name - 'Hunstein's Secret' - suggesting it was not exactly the same as the form found in Irian Jaya.

There is a tendency for westerners to misuse the word 'discover' but Craven and Rouse suggest that few if any humans would have seen this plant. The area is not settled and local nomads, at least after the 1960s, stick mostly to the rivers rather than high mountains.

The name Rhododendron x hunsteinii was published last year by George Argent from Royal Botanic Gardens Edinburgh, in the second edition of his Rhododendrons of the Genus Vireya. I haven't seen the book but I'm told by Andrew Rouse that molecular sequencing confirmed it is a hybrid between Rhododendron leucogigas and another species. Andrew did note on Saturday that 'it may well be a distinct species'. His flowering plant was struck from a cutting in 2004 and last flowered in 2009 - the beautiful picture at the top of the post was taken by Andrew then.

[I wouldn't normally include such an out-of-focus image but here is Andrew Rouse, to the right of Michael Hare, Convener of the Growing Friends Group, Melbourne Friends, Royal Botanic Gardens Victoria. Let's just say it was dark and misty, and the instability of my phone camera adds to the intrigue.]