Rhododendron macgregoriae



Rhododendron macgregoriae
at the Rhododendron Species Foundation (1983-074)

The story of Rhododendron macgregoriae begins in 1890 when a Mr. Belford, accompanying Sir William MacGregor on the first recorded ascent to the highest summit of the Owen Stanley Range, first collected specimens of a new species of Rhododendron at 3350m on Mount Yule in New Guinea. Dried material was sent to Baron Ferdinand von Mueller, Government Botanist in Victoria, Australia, who the following year published a description of the plant in the Journal of Botany (J.Bot. 29: 177), naming it for Lady MacGregor, wife of Sir William MacGregor, the first Lieutenant-Governor of New Guinea. It was to be another 65 years, however, before Rhododendron macgregoriae would be introduced into cultivation when, in 1955, wild collected seed was distributed by the Rijksherbarium at Leiden in The Netherlands.

Rhododendron macgregoriae - yellow form

The geographical distribution of Rhododendron macgregoriae is limited to New Guinea although the species is widespread across the whole island growing from only 500m up to 3350m altitude, preferring open sites in mossy forest or grassland.

In "Rhododendrons of Subgenus Vireya", Dr. George Argent classifies Rhododendron macgregoriae in section Euvireya and describes the species as a terrestrial shrub or small tree growing to 5m in height, bearing leaves elliptic to ovate in shape of up to 14cm in length by 5cm across.

Rhododendron macgregoriae

The flowers of Rhododendron macgregoriae are shortly tubular in shape, the corollas 2.5cm in length and up to 3cm across the extended lobes, carried in umbels of between generally 7 and 15 flowers. Flower colour is quite variable with yellow, orange, red and pink forms having been recorded, some with a contrasting central "eye" of orange or yellow. The yellow and orange forms are more common, especially in cultivation, whilst the red and pink forms are rarely seen in Papua New Guinea, tending to occur more frequently on the western side of the island of New Guinea.

Rhododendron macgregoriae
at the Royal Botanic Garden Kew

In New Guinea, plants of Rhododendron macgregoriae growing at low elevations in areas under cultivation by the local inhabitants are considered to be weeds and also known as poisonous to grazing livestock. This toxicity is harnessed by the villagers in dealing with any local rat populations by mixing the flowers with sweet potato to make an effective bait.

Rhododendron macgregoriae x Rhododendron inconspicuum
at the Royal Botanic Garden Edinburgh

Rhododendron macgregoriae is believed to be pollinated by butterflies and indeed hybridises freely in the wild, principally with Rhododendron zoelleri, R. dielsianum and R. inconspicuum. Two hybrids with the latter species, grown from wild collected seed, are pictured (above and bottom). One, R. macgregoriae x R. inconspicuum, is light pink with a creamy yellow eye, whilst the other, the reverse cross, is a darker shade of pink and considered of sufficient merit to be named and registered as Rhododendron 'Sweet Mac'.

Widely grown by Vireya enthusiasts around the world, Rhododendron macgregoriae is generally considered one of the easiest species to grow and flower in cultivation and has also proved to be a popular choice of parent with hybridisers. Today, nearly one hundred named cultivars are of "mac" descent, many of them retaining the distinctive appeal of this parent together with its reliable, free-flowering habit. A selection of photographs of hybrids produced using Rhododendron macgregoriae as either seed parent (above) or pollen parent (below) illustrates the range of colour and form now available to growers.