Plant profiles > Hibiscus

Family : Malvaceae

Within conservation, there are certain plants or animals that are referred to as 'flagship species'. Such species play an important role. The attention that they attract (by virtue of their outstanding characteristics) helps draw the public's gaze to the plight of less spectacular species, and often acts as a catalyst for protection measures that benefit a wide range of species. Flagship species usually conform to two criteria; firstly, that their plight is acute, and secondly, they are striking in appearance or character.

Based on these criteria, puarangi (Hibiscus richardsonii) is a textbook example of a flagship species - critically endangered in the wild, it is also one of our most conspicuously beautiful native flowers. In addition to the appeal of its flowers, this herb is particularly desirable for its compact growth habit and ease of culture.

Its relative, Hibiscus diversifolius ssp. diversifolius, bears similarly attractive flowers, but is not as well suited to widespread cultivation - due to its large size, spreading habit and prickly stems. This species is, however, worthy of consideration for spaces in which its muscular appearance is appropriate - such as some kinds of wetland habitats in which it is naturally found, or gardens of a subtropical nature.

Both of our native species of Hibiscus are found naturally in isolated pockets of the northern half of the North Island, and are therefore most appropriate for warmer parts of the country - although H. richardsonii makes an attractive annual in cold climates.

Hibiscus is a widespread genus, that reaches its southern limit in New Zealand. The family to which Hibiscus belongs, the mallow family (Malvaceae), is represented in New Zealand by three other genera; Entelea, Hoheria and Plagianthus (all of which form trees).

Hibiscus richardsonii
Native hibiscus; Puarangi

The road to understanding this plant is an interesting story, in which its status as an indigenous species was long questioned. To summarise it briefly, Hibiscus richardsonii was previously assumed to be part of H. trionum (a species now considered to be introduced). However, after some botanical detective work, it has now been classified as a separate species.

The difference between these two otherwise similar plants is that H. richardsonii has smaller flowers, lacks the characteristic dark blotching of H. trionum's flowers, and H. richardsonii has smaller, more finely serrated leaves1. Another important difference is that H. richardsonii is the true native species of puarangi.

The suspicion that they might be separate entities was founded upon the differences between the "blotched" and "unblotched" forms of what was then understood to be H. trionum2. Peter de Lange and Colin Ogle, two prominent figures within New Zealand plant conservation, had separately noted the "unblotched" form growing in remote locations. The isolated nature of many of the occurrrences of this form was a good indicator of its indigenous status, as was the fact that it is the only form mentioned by botanists prior to 1860.

Taxonomic work was then undertaken in conjunction with an Australian scientist, Lyn Craven, and H. richardsonii was assigned as a distinct species that is endemic to New Zealand and eastern Australia. In New Zealand, it is associated with the eastern coastline of the upper North Island, where it inhabits disturbed coastal habitats (such as seabird colonies), as well as scrub and open forest. It is listed in the highest threat ranking, 'Nationally Critical', and is therefore a plant that should occupy a prominent place in the national consciousness.

It is eminently suited to garden use, for it grows equally as well as its near relative, H. trionum. It should be noted here that it is important that the two species are not grown together, as they hybridise readily - a factor that constitutes a potential threat for acutely endangered species such as this.

Hibiscus richardsonii is best suited to an open aspect within the garden, and it has been observed before that it is a very attractive species for flower gardens. It is normally a relatively short-lived perennial in warmer areas, but is best treated as an annual in cold parts of the country. It readily self-seeds, and is therefore a useful 'filler' plant. Late in its flowering season, growth can become somewhat open. Consequently, plants respond well to judicious pruning, to maintain a compact growth habit in their following growth phase.

In addition to the beauty of the flowers, the ease with which Hibiscus richardsonii grows (from either seed or nursery-grown plants) makes it an ideal candidate for encouraging children to grow plants. It also holds significant potential as a native bedding plant - a category of plants that currently consists entirely of garish exotic species.

The specific epithet, richardsonii, is not actually derived from a New Zealand botanical figure. As the species is also native to eastern Australia, it was initially described off collections made by a 19th Century horticulturist, John Richardson - an Englishman who was sent to Australia as a convict, and was subsequently employed as a gardener and plant collector.

 


Footnotes

  1. As noted on the website of the NZ Plant Conservation Network, www.nzpcn.org.nz.
  2. A full account of the process of ascertaining the taxonomic status of H. richardsonii and H. trionum was provided by Peter de Lange, within the NZ Plant Conservation Network's newsletter, Trilepidea - from which we have garnered certain details regarding those investigations (Trilepidea No. 59. October 2008. NZPCN).