Megaherbs are a group of herbaceous wildflowers growing in the New Zealand subantarctic islands and on the other subantarctic islands. They are characterised by their great size, with huge leaves and very large and often unusually coloured flowers, which have evolved as an adaptation to the harsh weather conditions on the islands. They suffer from overgrazing due to introduced mammals.
Originally, the term was coined to describe large-leaved herbs that form meadows in the subantarctic islands [1] but has also been applied to describe tropical alpine vegetation forms [2] found in the Andes, East Africa and New Guinea. [3] They are large herbs that can reach dimensions of over one metre, often feature strikingly colourful flowers, [4] [5] large leaves and long stalks, [6] and are important components of the ecosystems of the subantarctic islands. [7] Beyond these traits, megaherbs can have different forms; [8] for example, some genera have perennial leaves and others are deciduous. [9] Intensely coloured flowers are not unique to megaherbs but also occur on other plant species in the same environments [10] and either arose by chance or are evolutionary adaptations to the environment. [11]
They live in the wet, windy and cold environments of the subantarctic islands, where they coexist with cushion plants and tussock grasses but trees are absent. A single species, Pleurophyllum hookeri , covers almost a third of Macquarie Island [12] where another megaherb, Stilbocarpa polaris , also occurs. [13] They reach their maximum extent on that island. [14] The only subantarctic islands lacking them are the Falklands and South Georgia, but Poa flabellata on South Georgia could be considered a megaherb. [15] Typical settings are water-rich with fertile soils; sometimes they are associated with volcanic heat sources. [16] On Campbell Island they appear to occur preferentially in nutrient-rich (eutrophic) terrain. Researchers since the 1940s often incorrectly assumed that they are limited to cliffs and ledges, as grazers had extirpated them from other areas. [17]
The most extraordinary of the megaherbs is the Pleurophyllum meadow, a community dominated by the large-leafed herbaceous composite, producing a floral display second to none outside the tropics
They are the best known plants of the New Zealand subantarctic islands [18] and are important components of the biodiversity of the region. [2] Another name is "megaphyllous herbs". [3]
Common taxa forming megaherbs are Asteraceae, Apiaceae, Araliaceae, Asphodelaceae, Asteraceae, Boraginaceae, Brassicaceae, Gentianaceae and Liliaceae; sometimes Poaceae (grasses) are also included. [15] [19] In the New Zealand subantarctic islands, four endemic genera make up megaherbs. Among these are Anisotome and Bulbinella with colourful flowers and Pleurophyllum and Stilbocarpa with large leaves. [18] [20] Additional genera are Gentianella [21] and Pringlea . [7]
Note megaherb species are the Campbell Island carrot ( Anisotome latifolia ) and the Ross lily ( Bulbinella rossii ). [22] The Chatham Island forget-me-not (Myosotidium hortensia) naturally occurs on the Chatham Islands but has been brought to New Zealand. It has large leaves and forms rosettes up to one metre wide. [23] The Kerguelen cabbage (Pringlea antiscorbutica) is a megaherb species that occurs on Heard Island where it is a key species in herbfields, Iles Crozet, Iles Kerguelen, Marion Island and Prince Edward Island. [24]
Other species called "megaherbs" include Phormium colensoi on New Zealand. [25] The Mountain buttercup (Ranunculus lyallii) is also considered a megaherb [26] and Astelia solani has been referred to as one. [27] The species Aciphylla latifolia , Bulbinella rossii , Myosotidium hortensia, Pleurophyllum spp. and Stilbocarpa in the Chatham Islands have been referred to as "macrophyllous forbs". [28] Finally, Angelica archangelica in Iceland has been considered an example of a Northern Hemisphere megaherb. [15]
The origins of the megaherb growth form are enigmatic. Several different subantarctic genera independently evolved this trait, which is defining for the genus Pleurophyllum. [20] Stilbocarpa megaherbs evolved from ancestors with smaller leaves. [29] These plants survived the last glacial maximum on the subantarctic islands and spread northward after its end. [30] Related species also occur on New Zealand. [31]
Megaherbs have been described as a form of gigantism. [21] The evolution of the megaherb form may be a consequence of specific conditions in the subantarctic islands. [20] [4] The large leaves could be intercepting nutrient-bearing aerosols and trap heat in cold environments. Rosette growths reduce wind speeds and wind-driven evaporation and cooling. [31] The leaves may also act to absorb heat from diffuse radiation [17] and higher temperatures have been measured in megaherbs than the surrounding environment. [32] At the same time, the lack of herbivores, plentiful water and nutrients brought by e.g seabirds and steady temperatures facilitate the growth of large plants. [29] [15] On Adams Island megaherbs are well developed where they are fertilized by guano. In return, birds use them as cover and source of insects [33] and are burrowed by nesting birds. [34] Such burrowing may influence the establishment of megaherb communities. [35] They are among the first plants to resettle former albatross nests on Adams Island. [36] The simultaneous occurrence of large leaves, large underground storage tissues, large seeds and large seed output is also found in megaherbs and appears to reflect unusual adaptations, as resource trade-off would normally prohibit their simultaneous occurrence. [7]
Herbs with large leaves occur in other places such as Chile, Hawaii, Kenya and New Zealand but there are traits specific for subantarctic megaherbs [37] [30] and there are environmental differences, such as lower and more steady insolation. [38] Their evolution may be driven by similar environmental factors that are encountered on high mountains and in polar climates, [29] such as cold and windy weather, and may thus be examples of convergent evolution. [39]
Wētā, flightless crickets of New Zealand, have been observed to pollinate megaherbs and may constitute their main pollinators. [40] Moths have also been observed pollinating megaherbs. [41]
Megaherbs were first described by the British botanist Joseph Dalton Hooker, who coined the term in 1847. [1] Megaherbs draw the interest of scientists and tourists alike; [16] they are the main claim to fame of Campbell Island for example. [42] The Fairchilds Garden site on Adams Island was noted already in 1891 for its megaherbs. [33] The characteristic appearance makes Pleurophyllum a plant that could be used in horticulture, but attempts to cultivate it outside of the subantarctic environment have largely been unsuccessful. [20]
Megaherbs are susceptible to overgrazing by mammals. [17] Feral pigs have devastated megaherb communities on Auckland Island. [43] On Macquarie Island, rabbits consume megaherbs while rats cache seeds of Pleurophyllum hookeri [44] in places unsuited for their germination, [45] and the growth of the rabbit population has resulted in a major reduction of megaherb populations, as well as of other plant taxa of the island. [46]
Where grazing animals have been removed, megaherb species often quickly reoccupy the terrain. [31] This is expected to occur on Macquarie Island after rabbit and rodent populations [47] began to shrink since 2010. They will probably displace less edible but also less competitive plant species like Agrostis magellanica and Acaena magellanica . [44] Conversely only a partial recovery took place on Campbell Island by 1994. [48]
The term "megaherb" is sometimes used to describe plant species from other continents that have features similar to subantarctic megaherbs. [49] It has also been used to describe members of the family Heliconiaceae, which are tropical species, [50] and for the Amazonian species Phenakospermum guyannense . [51]
The Auckland Islands are an archipelago of New Zealand, lying 465 kilometres (290 mi) south of the South Island. The main Auckland Island, occupying 510 km2 (200 sq mi), is surrounded by smaller Adams Island, Enderby Island, Disappointment Island, Ewing Island, Rose Island, Dundas Island, and Green Island, with a combined area of 626 km2 (240 sq mi). The islands have no permanent human inhabitants.
Auckland Island is the main island of the eponymous uninhabited archipelago in the Pacific Ocean. It is part of the New Zealand subantarctic area. It is inscribed in the UNESCO World Heritage list together with the other New Zealand Subantarctic Islands in the region.
Campbell Island / Motu Ihupuku is an uninhabited subantarctic island of New Zealand, and the main island of the Campbell Island group. It covers 112.68 square kilometres (43.51 sq mi) of the group's 113.31 km2 (43.75 sq mi), and is surrounded by numerous stacks, rocks and islets like Dent Island, Folly Island, Isle de Jeanette-Marie, and Jacquemart Island, the latter being the southernmost extremity of New Zealand. The island is mountainous, rising to over 500 metres (1,640 ft) in the south. A long fiord, Perseverance Harbour, nearly bisects it, opening out to sea on the east coast.
Jacquemart Island, one of the islets surrounding Campbell Island in New Zealand, lies 1 km south of Campbell Island and is the southernmost island of New Zealand.
Bulbinella is a genus of plants in the family Asphodelaceae, subfamily Asphodeloideae, first described as a genus in 1843. Many species are endemic to Cape Province in western South Africa, confined to the winter rainfall area. Other species are endemic to New Zealand, where they are most common in the central Otago region which enjoys a similar climate to the Cape Region of South Africa.
This is a list of taxa comprising the flora of the Antipodes Islands. It includes some species known as megaherbs.
The Auckland Island pig is a feral landrace of domestic pig found on subantarctic Auckland Island, New Zealand. Its ancestors have inhabited the island since 1807, and, as an invasive species, has had a considerable environmental impact.
Damnamenia is a genus of flowering plants in the family Asteraceae.
Pleurophyllum is a genus of subantarctic plants in the tribe Astereae within the family Asteraceae.
Pleurophyllum hookeri, also known as the silver-leaf daisy or sage-green rosette herb, is a herbaceous plant in the family Asteraceae, a megaherb native to the subantarctic Auckland and Campbell Islands of New Zealand and Australia’s Macquarie Island. It grows up to 900 mm in height and has crimson button flowers and long, silky, silver leaves, with a large carrot-like tuber and long roots. It also has the unusual feature of a vertically contractile stem, most of which is underground, which serves to keep the leaf rosette close to the ground surface and the plant anchored securely against the very strong winds typical of subantarctic islands. Prior to the successful eradication of introduced mammals on Macquarie Island in 2011, it had been threatened there by black rats and European rabbits.
Azorella polaris, commonly known as the Macquarie Island cabbage, is a species of flowering plant usually placed in the family Araliaceae and only very distantly related to cabbage. It is a megaherb, growing up to about a metre in height, native to the subantarctic islands of New Zealand and to Australia’s Macquarie Island.
Polystichum vestitum, commonly known as the prickly shield fern or pūnui (Māori), is a hardy, evergreen or semi-evergreen ground fern.
Bulbinella rossii, commonly known as the Ross lily, is a species of flowering plant in the genus Bulbinella. Despite its common name, it does not belong to the lily family Liliaceae. It is one of the subantarctic megaherbs. The specific epithet honours British Antarctic explorer James Clark Ross, who visited Campbell Island in December 1840. Bulbinella rossii is featured on the reverse of the current five dollar New Zealand banknote.
Anisotome latifolia, commonly known as the Campbell Island carrot, is a species of plant in the genus Anisotome of the carrot family (Apiaceae). It is native to the Auckland and Campbell Islands in the subantarctic regions of the South Pacific.
Pleurophyllum criniferum is a species of flowering plant in the family Asteraceae that is endemic to the subantarctic islands of New Zealand.
Myosotis antarctica is a species of flowering plant in the family Boraginaceae, native to mainland New Zealand, Campbell Island and southern Chile. Joseph Dalton Hooker described the species in his 19th century work Flora Antarctica. Plants of this species of forget-me-not are perennial with a prostrate habit, bracteate inflorescences, and white or blue corollas. It is one of two native species of Myosotis in the New Zealand subantarctic islands, the other being M. capitata, which also has blue corollas.
Plantago aucklandica is a species of flowering plant in the family Plantaginaceae that is endemic to the subantarctic Auckland Islands, New Zealand. Joseph Dalton Hooker described P. aucklandica in his Flora Antarctica in 1844. Plants of this plantain are large with large leaves, up to seven veins, wide petioles, colliculate seeds, and long spikes with dozens of flowers and one-seeded fruits. This species in considered to be At Risk - Naturally Uncommon, as it is an island endemic with a restricted range.
Carex erebus is a member of the sedge family and is found on the Antarctic Islands of Australia and New Zealand.
Ichneutica erebia is a moth of the family Noctuidae. This species is endemic to New Zealand and is found on Campbell Island and the Auckland Islands. Adults of this species are on the wing from August to January. The adults are variable in appearance but can be distinguished from similar species by the patters or lack thereof on their forewings. The larvae of I. erebia are polyphagous and hosts include Pleurophyllum criniferum, species within the genera Stilbocarpa and Carex, as well as Chionochloa antarctica, Urtica australis and Raukaua simplex.
Myosotis antarcticasubsp. antarctica is a subspecies of flowering plant in the family Boraginaceae, native to New Zealand, Campbell Island, and southern Chile. Joseph Dalton Hooker described the species in his 19th century work Flora Antarctica. Plants of this subspecies of forget-me-not are perennial with a prostrate habit, bracteate inflorescences, and white or blue corollas. It is one of two native Myosotis in the New Zealand subantarctic islands, the other being M. capitata, which also has blue corollas.
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