Friday, December 18, 2009

Hibiscus insularis

Hibiscus insularis | Phillip Island Hibiscus

Hibiscus insularis is endemic to Phillip Island in the Norfolk Island Group, where the species is confined to three patches on the northern slopes (Green 1994; Mosley 2001). These plants have survived despite the grazing pigs, goats and rabbits which destroyed most of the Island's vegetation. With all of the introduced animals now removed from Phillip Island, seedlings are now growing near the original bushes. Hibiscus insularis was down to three or four bushes, and was in danger of extinction until cuttings were sent to the Sydney Botanical Gardens.

Although the species is listed as Critically Endangered (under the Australian Government's Environment Protection and Biodiversity Conservation Act 1999), it is now well established in cultivation. Hibiscus insularis is a dense bushy shrub to 4m. The 6-9cm blooms are produced freely in late summer and autumn. The flowers have cream colored petals which turn to a light purplish rose color with age. The crimson stigma pads are pronounced for a small flower. This Hibiscus is ideal for growing in coastal areas and is reasonably salt tolerant. Apparently, the plant retains a juvenile form for up to 10 years, with smaller leaves. Australian sources relay that it may take a number of years before the young plants reach maturity and they begin to bloom for the first time. For more information on Hibiscus insularis, see this excellent article: Hibiscus insularis

Historical Reference: Hibiscus insularis endemic on Phillip Island. A few plants still remain on the island, but those that I saw were in a most unhealthy condition, being covered with coccids, aphides, smuts, and other blights and pests. They were obviously maintaining an unequal struggle with an unfavourable environment.

   Transactions of the Royal Society of New Zealand
   Vol. XLVII, July 1915

Reference: It is not certain when rabbits were introduced to Philip but HOARE (1968) showed they were present in numbers in 1838. Today the vegetation is virtually absent. There are a few white oaks (Lagunaria) in the moister central valley, a straggly clump of Hibiscus insularis, and a few weeds, many of which are not native. A few scrawny rabbits remain. HOARE (1968) stated the pigs and goats were not exterminated until well into the third phase of settlement. One can surmise that the populations of these built up, possibly neglected in the early years of the third phase whilst the Pitcairners were settling in to their new home. Regeneration of shrubs would have been prevented and dry spells would have led to the goats reaching for the mature foliage of the scrub and the pigs grubbing for roots and gnawing at bark. Coupled with the island's natural tendency for soil erosion, these factors could have led to the gradual decline of the vegetation to a level where the larger herbivores might have died out naturally. Should the rabbits finally be exterminated, CUNNINGHAM'S notes provide a guide for efforts to restore the natural vegetation, though the Streblorrhiza and the topsoil are lost.

Philip now stands pinkly to the south of Norfolk, the pink relieved only by a few dark dots of vegetation. Numerous seabirds nest there and tourists come to marvel at the variety of hues of red, orange and yellow of the exposed subsoil. The fate of Philip Island should be borne in mind when considering the changes that have occurred and are still occurring on the main island.

   Series Entomologica
   Volume 13 of The Lepidoptera of Norfolk Island: Their Biogeography and Ecology
   Jeremy Daniel Holloway, Springer, 1966