Megaherb

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Megaherbs are a group of herbaceous perennial wildflowers growing in the New Zealand sub-antarctic islands. They are characterised by their great size, with huge leaves and very large and often unusually-coloured flowers, which have developed as an adaptation to the harsh weather conditions on the islands. Livestock introduced to the islands in the 19th century severely reduced the megaherb population, to such an extent that by the late 20th century the megaherbs were threatened with extinction. Since the removal of the livestock in 1993, the megaherbs have regenerated successfully and dramatically. They have been described as "the outstanding botanical experience of New Zealand".

1 Distribution and history
2 Megaherb species
3 Companion plants in megaherb communities
4 Threat to megaherbs
5 See also
6 Sources
7 External links

[edit] Distribution and history

Megaherbs occur on many of the sub-antarctic islands of New Zealand, predominantly on the Snares island group, the Auckland Islands and the Campbell Island group. Here these extraordinary plants evolved in response to the climatological and soil conditions and the lack of herbivorous predators on the islands. The weather is largely wet, cold and extremely windy; the soil peaty, acidic and impoverished. The almost continual cloud-cover means that the islands experience low light levels.

The term 'megaherb' was first used by Sir James Clark Ross during his 1839 – 1843 Antarctic expedition. Sir Joseph Hooker, the expedition’s botanist, wrote that the megaherbs produced "a floral display second to none outside the tropics". Although small in size when compared to plants found in the tropics, megaherbs are notable because their size is far greater than other herbaceous perennials found growing in the sub-antarctic islands: generally the harsh weather and soil conditions experienced there have a stunting effect on plants.

[edit] Megaherb species

Most sub-antarctic megaherbs flower en masse in a cycle of approximately three years; in "off" years a few plants will flower but with nowhere near the effect created by the mass flowering. A visitor in December 1996 (Derek Fell) described a megaherb meadow on Campbell Island: 'We stood in disbelief ... a stupendous carpet of flowers stretched as far as the eye could see'. The following plants are some of the more prevalent megaherb species.

A major component of megaherb communities is the Bulbinella rossii (Ross lily). This clump-forming plant has strap-like and succulent leaves, growing to 60cm. The bright yellow flowering spikes are carried on up to 90 cm high stems. Its nearest relatives appear to be B. hookeri (Maori lily) from the New Zealand mainland, and B. floribunda (yellow cat-tail) from South Africa.

Anisotome latifolia (Campbell Island carrot) bears pink flowers in huge clusters which can reach 75 cm across, on stems up to 1.5 m.

Pleurophyllum speciosum (Campbell Island daisy) is an extraordinary plant, and appears to be closest related to the Cineraria daisies of Africa and the Canary Islands than any others. It forms an enormous rosette, up to 1.2 m across, of huge, broad pleated leaves. It bears pinkish-purple to pale lilac flowers with maroon centres, held on flower stems up to 60 cm tall. Two other Pleurophyllum species, P. hookeri and P. criniferum (giant button daisies) are also megaherbs, reaching 90 cm in height and with similar broad leaves. The flowers of P. hookeri are crimson whilst those of P. criniferum are near-black. Natural hybrids between these species have been recorded.

The Black-eyed daisy Damnamenia vernicosa bears white flowers that are 5cm wide, although the plant itself grows only to 10cm high.

Stilbocarpa polaris (Macquarie Island cabbage) is a member of the Aralia family. It grows in clumps to 90 cm tall with fluted, rhubarb-like leaves and lime green flower clusters up to 60 cm wide.

[edit] Companion plants in megaherb communities

Growing alongside the megaherbs are other plants, such as hebes, daisies, amber sedge, and two species of gentian: Gentianella cerina (giant gentian), growing to 15cm tall with flowers 2.5cm across, varying in colour from white to pale pink, red and purple; and G. concinna, with pinkish red flowers.

[edit] Threat to megaherbs

The New Zealand sub-antarctic islands are uninhabited by humans (apart from scientific research staff at a meteorological station on Campbell Island). In the nineteenth century, foraging livestock including rabbits, pigs, sheep, goats and cattle were introduced. This was undertaken in order to provide support for any castaways that might be shipwrecked in this area of notoriously treacherous sea conditions - the roaring forties and furious fifties.

The feral livestock populations increased to such an extent that their grazing seriously depleted the megaherbs. Action was taken in 1987 by the New Zealand Department of Conservation to remove all introduced species, by 1993 this was completed. The speed and extent of the regeneration witnessed in 1996, a mere three years later, astonished visiting botanists.

The collection of megaherbs is prohibited. It has been noted that specimens of legally-collected megaherbs growing in botanic gardens at Invercargill on New Zealand’s South Island seem sickly and puny compared to the wild populations. Megaherbs have evolved to grow in the very specific set of weather and soil conditions experienced on the sub-antarctic islands, and so fail to thrive in seemingly more benign conditions.

[edit] See also

Island gigantism

[edit] Sources

Fell, Derek, (May 1998) "Megaherbs of the far south" The Garden (Journal of the Royal Horticultural Society) 123(5):326-329
Hooker, J. D. (1844) The Botany of the Antarctic Voyage of H.M. Discovery Ships Erebus and Terror in the Years 1839-1843, Under the Command of Captain Sir James Clark Ross; Volume 1: Flora Antarctica; Pt. 1: Botany of Lord Auckland’s Group and Campbell’s Island. Reeve, London
Mitchell, A. D., Meurk, C. D. and Wagstaff, S. J. (1999) "Evolution of Stilbocarpa, a megaherb from New Zealand's sub-antarctic islands" New Zealand Journal of Botany 37:205-211 (online at https://www.rsnz.org/publish/nzjb/1999/22.pdf)
Nicholls, V. J. and Rapson, G. L., (1999) "Biomass allocation in subantarctic megaherbs, Pleurophyllum speciosum (Asteraceae) and Anisotome latifolia (Apiaceae) New Zealand Journal of Ecology 23(1):87-93 (online at http://www.nzes.org.nz/nzje/free_issues/NZJEcol23_1_87.pdf)
Smith, Philip, (November 2006) "Islands of Diversity" The Garden (Journal of the Royal Horticultural Society) 131(11):756-757