This is the Puka, or Meryta sinclairii, a species growing naturally only on Three Kings islands off the far north of the North Island of New Zealand. These islands are at a latitude of 34 degrees south, pretty much the same as Sydney.
A New Zealand species with subtropical attitude, it is dotted all over Melbourne's Royal Botanic Gardens. And as you'd expect from something in the ivy family (Araliaceae), it's not about the flowers. Nineteenth century Director William Guilfoyle knew this. The Puka was part of his plan to contrast leaves of varying shape, size, texture and colour.
As pointed out in the booklet A Gallery of Plants (1992) by Ros Semler, this species is a distinctive element in the garden beds around the Nymphaea Lily Lake, all of which continue to display Guilfoyle's design intent in regard to diverse foilage. Meryta sinclairii rates a mention in most books on Melbourne's Royal Botanic Gardens.
The leaves are chunky and at first blush a little like those of some mangroves, such as Clusia. In its native habitat it grows mostly in sheltered, moist valleys but it seems to do well out in the open and with minimal watering, albeit with a little leaf burn off in the Melbourne summer (this next picture, and others from the Royal Botanic Gardens, were taken in mid-January).
Our plants flower, although I don't know how regularly. There are separate male and female flowers, both nondescript, with the female flowers followed by ivy-like berries. I found some flower buds (in January) on a bush on the Ornamental Lake side of what we call the Central Lawn, but only a few remaining fruit. Here is a picture of those precient buds, followed by an picture of young fruit on a specimen growing in New Zealand, photographed by Warren Brewer (©)
According to the online Flora of New Zealand, Puka was first collected for science from a single plant growing at Paparaumu, in the Whangaruru Harbour, about 150 km north of Auckland. The soon to become Director of Kew Gardens in London, Sir Joseph Hooker, described it as a new species in 1852, in a genus called Botryodendrum. That genus has since been split and subsumed, with most species relegated to Meryta which now has about 28 species.
The Wikipedia entry has a ring of authenticity about it so I'll chance repeating this tale. William Colenso, the first European to find the specimen at Whangururu Bay was frustrated in his attempts to collect flowers and fruits - he visited regularly over a number of years but found none. Both he and the Colonial Secretary Andrew Sinclair sent leafy stems to Sir Joseph who eventually got fertile material, off the same tree, from a William Mair.
From the same source I can report that the Puka has the largest entire (that is, not divided into smaller leaflets) of any New Zealand plant. Sounds about right, and supported by a comment reiterated by Ross Beever in his paper on the natural distribution of the species, that the Puka is the only 'true macrophyll' in the New Zealand flora.
Most of the 28 species of Meryta are found in the tropics and subtropics, with a whopping 11 found in, and only in, New Caledonia (a lot, but two fewer than there are Araucaria species there...). There are no species native to mainland Australia or mainland New Zealand - just the one species, the Puka, on the Three Kings Islands (and introduced onto the nearby Hen and Chicken Islands) and two (Meryta angustifolia, Meryta latifolia) on the more-or-less-self-governed Australian territory of Norfolk Island.
Meryta sinclairii is uncommon and at risk of extinction in its natural habitat. The New Zealand Plant Conservation Network - an at all times thoroughly reliable source of information - note that the remnant natural populations are under threat from marijuana growers who like using remote islands to grow their crops. It's not that the ganja outcompetes the puka, but the illegal farmers often bring with them deadly (to the Puka) fungal pathogens.