Tasmanian cushion plants

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Donatia novae-zelandiae in flower, Cradle Mountain Lake Saint Clair National Park, Tasmania. Photographer: Kinara Johnson. Cushionplantflowers.JPG
Donatia novae-zelandiae in flower, Cradle Mountain Lake Saint Clair National Park, Tasmania. Photographer: Kinara Johnson.

Tasmanian cushion plants are low growing, highly compact, woody, spreading mats that can grow up to 3 m in diameter, located mainly on the island of Tasmania. These mats are made up of tightly packed stems that grow at the same rate so that no apical rosettes protrude above the rest. The term cushion plant refers to a characteristic growth habit adopted by various species from a range of families to adapt to alpine and subalpine environments and areas of high latitude. [1] They are adapted to grow in low nutrient areas and typically have deep taproots. Cushion plants are very slow growing and do not grow high above ground; mounds typically remain under 30 cm high. Underneath the living surface of the cushion, the plants either allow dead leaves to persist or produce non-photosynthetic material, resulting in an insulating effect.

Contents

Floristics of Tasmanian cushion plant community

Six families, including seven species, of cushion plants occur in Tasmania, and one additional family and species occur on Macquarie Island. Three additional families, including seven species, can adapt to the bolster habit, although not exclusively. The cushion plant growth habit is linked with drainage and the plant's ability to redirect water flow due to its growth pattern. [2]

FamilyScientific name [3] Common name [3] Description
AsteraceaeAbrotanella forsteroidestasmanian cushionplantEndemic to Tasmania. Leaves are bright green, crowded, thick and sheathing from the base to a pointed tip. Flowers are a tiny white daisy held just above the leaves. [4]
Pterygopappus lawrenceisage cushionplantEndemic to Tasmania. A compact sage blue/green cushion; leaves are tiny, thick and closely overlapping, broadly spathulate with pointed tips and a silky, hairy base. Flowers are a terminal single white daisy held just above foliage. [4]
CaryophyllaceaeColobanthus pulvinatuscushion cupflowerA compact, rigid cushion plant with stiff, prickly leaves with thickened margins, 2 – 5 mm long. Flowers are solitary with yellow/green cup-shaped sepals tucked in the foliage. [4] Listed as rare under the Threatened Species Protection Act 1995. [5] Also found in NSW. [6]
DonatiaceaeDonatia novae-zelandiaesnow cushionplantBright green, hard and compact cushion. Leaves are linear, fleshy and pointed, 5 – 6 mm long, with fine hairs at the base. Solitary flowers have 5 white petals and grow at the same level as the leaves. Also found in New Zealand. [4]
EpacridaceaeDracophyllum minimumclaspleaf heathEndemic to Tasmania. Densely branched, compact, hard, mounding cushion. Leaves are thick and rigid, broad, sheathing and slightly concave with a hard point. White, solitary tubular flowers sit directly on top of foliage. [4]
ScrophulariaceaeVeronica ciliolate Previous name: Chionohebe ciliolateBen Lomond cushion plantEndemic to Tasmania. Soft, compact, rounded cushion. Leaves are light green and in dense basal rosettes, 2.5 – 4 mm long, 2 mm wide, pointed, with a tuft of silky hairs at tip. Flowers have 5 white petals and two groups of stamen fused to the petal tube. [4] Veronica ciliolate subsp. Fiordensis is listed as vulnerable under both the Threatened Species Protection Act 1995 and the Environment Protection and Biodiversity Conservation Act 1999. [7]
StylidiaceaePhyllachne colensoiYellow cushionplantA dense, tufted cushion plant with a distinct yellowish colour. Leaves are wider at the base and narrow to a blunt tip with a glandular pore, 3 – 4 mm long, densely packed around the stem. Flowers are white, single and terminal with 5-6 spreading lobes. The column is held above the petals. Also found in New Zealand.
Apiaceae Azorella macquariensis Macquarie cushionsEndemic and restricted to Macquarie Island. Leaf has reniform outline, with 3 or 5 lanceolate lobes, they are free to the base, acute and pungent, with a setose point. Flowers are bisexual and solitary; two leaf-like lanceolate bracts are fused at the base to form a cup. [8] Listed as endangered under the Threatened Species Protection Act 1995 and critically endangered under the Environment Protection and Biodiversity Conservation Act 1999. [9]

Evolution

The cushion plant is an example of convergent evolution. Unrelated species from a number of different families on separate continents have evolved the cushion form to adapt to similarly harsh environments.

Ecosystem function

Pterygopappus lawrencei and Dracophyllum minimum growing together, Cradle Mountain Lake Saint Clair National Park, Tasmania. Photographer: Kinara Johnson. Cushionplants.jpg
Pterygopappus lawrencei and Dracophyllum minimum growing together, Cradle Mountain Lake Saint Clair National Park, Tasmania. Photographer: Kinara Johnson.
Azorella macquariensis cushion plant on Macquarie Island. Azorella macquariensis.jpg
Azorella macquariensis cushion plant on Macquarie Island.

Cushion plants have been shown to be a keystone species in the ecosystem in which they occur. For example, Azorella macquariensis is the only cushion-forming plant that occurs on Macquarie Island and it plays a vital role in the ecosystem as it makes up the major structural component of feldmark vegetation on the island. [8] Cushion plants are also often considered "nurse species", as their presence is necessary in order for many other alpine species to become established. Cushion plants have been found to enhance species richness in areas with inherent impoverished local diversity. [1] This effect is due to their low and compact growth form that alleviates severe alpine conditions. [1]

Several Tasmanian cushion species have been found to have a surface temperature up to 10 °C greater than the ambient temperatures. [10] The warmer temperatures allow the plants to continue to photosynthesize and grow in conditions that would otherwise inhibit such productivity. This substantially extends the growing season. In addition, a combination of the insulating properties of past growth under the surface of the cushion plants and the peaty soils in which they grow prevents temperatures around the roots dropping below -1 °C, which stops the roots from freezing. [10] Surrounding plants species have adapted to not only benefit, but rely on these conditions the cushion plants provide to survive and grow, and are restricted to habitats in which cushions are present.

Threats

Three Tasmanian cushion plant species are listed as "under threat": Veronica ciliolata (subspecies fiordensis), Azorella macquariensis and Colobanthus pulvinatus.

Tasmanian endemic species, Veronica ciliolata subspecies fiordensis, is listed as vulnerable under both the Threatened Species Protection Act 1995 and the Environment Protection and Biodiversity Conservation Act 1999. [7] The total population of mature individuals is estimated to be from 1500 to 2000. [11] Threats include:

Azorella macquariensis, which is endemic to Macquarie Island, is listed as endangered under the Threatened Species Protection Act 1995 and Critically Endangered under the Environment Protection and Biodiversity Conservation Act 1999. [9] Since 2008, this species has encountered substantial dieback and has had a catastrophic decline in population size. [8] The cause of the dieback is unknown and under investigation. Once dead, the cushions may erode and as a result could have adverse impacts on the rest of feldmark vegetation due to its vital structural role in the ecosystem. Potential factors that threaten Azorella macquariensis include:

Colobanthus pulvinatus is listed as rare under the Threatened Species Protection Act 1995. [5]

Related Research Articles

Macquarie Island Sub-Antarctic island of Australia

Macquarie Island is an island in the southwestern Pacific Ocean, about halfway between New Zealand and Antarctica. Regionally part of Oceania and politically a part of Tasmania, Australia, since 1900, it became a Tasmanian State Reserve in 1978 and was inscribed as a UNESCO World Heritage Site in 1997.

Alpine tundra Biome found at high altitudes

Alpine tundra is a type of natural region or biome that does not contain trees because it is at high elevation. As the latitude of a location approaches the poles, the threshold elevation for alpine tundra gets lower until it reaches sea level, and alpine tundra merges with polar tundra.

Fellfield

A fellfield or fell field comprises the environment of a slope, usually alpine or tundra, where the dynamics of frost and of wind give rise to characteristic plant forms in scree interstices.

Bolster heath or cushion moorland is a type of vegetation community that features a patchwork of very low growing, tightly packed plants found at the limits of some alpine environments. The cushion plants form a smooth surfaced 'cushions' from several different plants, hence the common name of cushion heath. The cushion growth habit provides protection against the desiccating wind and help keep the cluster warm.

<i>Diselma</i> Genus of conifers

Diselma archeri is a species of plant of the family Cupressaceae and the sole species in the genus Diselma. It is endemic to the alpine regions of Tasmania's southwest and Central Highlands, on the western coast ranges and Lake St. Clair. It is a monotypic genus restricted to high altitude rainforest and moist alpine heathland. Its distribution mirrors very closely that of other endemic Tasmanian conifers Microcachrys tetragona and Pherosphaera hookeriana.

<i>Athrotaxis cupressoides</i> Species of conifer

Athrotaxis cupressoides, is also known as pencil pine, despite being a species of the family Cupressaceae, and not a member of the pine family. Found either as an erect shrub or as a tree, this species is endemic to Tasmania, Australia. Trees can live for upwards of 1000 years, sustaining a very slow growth rate of approximately 12 mm in diameter per year.

<i>Azorella selago</i> Species of flowering plant

Azorella selago is a species of cushion plant native to the sub-Antarctic islands of the Southern Ocean, including the Crozet Islands, the Possession Islands, the Heard Island and McDonald Islands, the Kerguelen Islands, and the Prince Edward Islands. The closely related Azorella macquariensis, which is endemic to Macquarie Island, was split from it taxonomically in 1989. A. selago is often a keystone species where it occurs and is well studied for its contribution to its native ecosystems.

Cushion plant

A cushion plant is a compact, low-growing, mat-forming plant that is found in alpine, subalpine, arctic, or subarctic environments around the world. The term "cushion" is usually applied to woody plants that grow as spreading mats, are limited in height above the ground, have relatively large and deep tap roots, and have life histories adapted to slow growth in a nutrient-poor environment with delayed reproductivity and reproductive cycle adaptations. The plant form is an example of parallel or convergent evolution with species from many different plant families on different continents converging on the same evolutionary adaptations to endure the harsh environmental conditions.

<i>Ewartia planchonii</i> Species of flowering plant

Ewartia planchonii, commonly known as creeping cushionherb, is an endemic herb to alpine areas of Tasmania. E. planchonii is commonly found in the western highlands of Tasmania. The Ewartia genus is described as cushion plants/herbs due to the characteristic growth habits of low growing, highly compact mats which are made up of highly packed stems. These mats are slow-growing and are often located in soils that contain low nutrients.

<i>Pterygopappus</i>

Pterygopappus is a genus of flowering plants in the tribe Gnaphalieae within the family Asteraceae. There is only one known species, Pterygopappus lawrencii, which is endemic to alpine Tasmania. It forms thick, light blue/green mats with densely packed leaves. It is most common in the mountains of the northeastern part of the island. It is a slow grower and prefers cool, moist environments.

<i>Azorella macquariensis</i> Species of flowering plant

Azorella macquariensis, also known as Macquarie azorella or Macquarie cushions, is a species of cushion plant endemic to Australia’s subantarctic Macquarie Island. It was referred to the more widely distributed Azorella selago until 1989, when it was described as a separate species.

Feldmark Plant community resilient to extreme winds

Feldmark, also spelt fjaeldmark, is a plant community characteristic of sites where plant growth is severely restricted by extremes of cold and exposure to wind, typical of alpine tundra and subantarctic environments.

<i>Colobanthus kerguelensis</i> Species of flowering plant

Colobanthus kerguelensis is a low-growing, moss-like flowering cushion plant in the family Caryophyllaceae, found on subantarctic islands in the southern Indian Ocean. The specific epithet refers to the type locality – the Kerguelen Islands.

Alpine vegetation refers to the zone of vegetation between the altitudinal limit for tree growth and the nival zone. Alpine zones in Tasmania can be difficult to classify owing to Tasmania's maritime climate limiting snow lie to short periods and the presence of a tree line that is not clearly defined.

<i>Richea gunnii</i> Species of flowering plant

Richea gunnii, the bog candleheath or Gunns richea, is an endemic Tasmanian angiosperm. It is a dicot of the family Ericaceae and is found in Central, Western and North-east Tasmania.

<i>Astelia alpina</i> Species of flowering plant

Astelia alpina called pineapple grass, silver astelia, or perching lily is a commonly found species in alpine and subalpine areas of Tasmania and the Australian Alps. It is a perennial herb that typically dominates its environment by growing in dense clusters, called mats, in alpine bogs. There are two subspecies: Astelia alpina var. novae hollandiae from New South Wales and Victoria and Astelia alpina var. alpina endemic to Tasmania. Both subspecies appear very similar to each other. The species was originally described by Robert Brown.

<i>Pherosphaera hookeriana</i> Species of conifer

Pherosphaera hookeriana, or Mount Mawson pine, is a dwarf conifer endemic to Tasmania, at altitudes above 600 meters. There are roughly 30 known sites, with population numbers in the tens of thousands. The species occurs in a range of habitats typically in areas near water bodies, mostly on dolerite derived soils. The species is highly fire sensitive and an increase in fire events associated with climate change may lead to local extinction and fragmentation of habitat.

<i>Olearia ledifolia</i> Species of shrub

Olearia ledifolia, commonly known as rock daisy bush, is a species of flowering plant of the family Asteraceae. It is endemic to Tasmania and found at higher altitudes where it grows as a low, compact bush with tough, leathery leaves and small white and yellow daisy-like "flowers" in summer.

<i>Dracophyllum minimum</i> Species of plant

Dracophyllum minimum, commonly known as heath cushionplant or claspleaf heath, is a species of bolster cushion plant endemic to Tasmania, Australia. It is a low growing, highly compacted plant with white flowers, commonly found in alpine areas of the south, centre and west of Tasmania.

<i>Ewartia meredithiae</i> Tasmanian endemic plant species

Ewartia meredithiae, commonly known as the rusty cushion plant, is a Tasmanian endemic cushion plant species. Out of the four species in Australia from this small genus, Tasmania has three, all of which are low growing, alpine species.

References

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  2. Reid, J. B.; Hill, R. S.; Brown, M. J.; Hovenden, M. J., eds. (1999). Vegetation of Tasmania. Number 8 in Flora of Australia Supplementary Series. Australian Biological Resources Study. ISBN   9780642568014.
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  6. "Colobanthus pulvinatus" . Retrieved 13 July 2021.{{cite web}}: CS1 maint: url-status (link)
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  8. 1 2 3 4 "Azorella macquariensis". Threatened Species Link. Tasmanian Department of Primary Industries, Parks, Water and Environment. 2012.{{cite web}}: CS1 maint: url-status (link)
  9. 1 2 "Azorella macquariensis — Macquarie Azorella, Macquarie Cushions". Species Profile and Threats Database. Australian Department of Agriculture, Water and the Environment. 2021. Retrieved 2021-07-13.{{cite web}}: CS1 maint: url-status (link)
  10. 1 2 Gibson, Neil (1988). A study on the biology of four Tasmanian cushion species (PhD thesis). University of Tasmania.
  11. "Veronica cilolata subsp. fiordensis". Threatened Species Link. 2016. Retrieved 13 July 2021.{{cite web}}: CS1 maint: url-status (link)
  12. Pendlebury, S.; Barnes-Keoghan, I. P. (2007). "Climate and climate change in the sub-Antarctic". Papers and Proceedings of the Royal Society of Tasmania. 141 (1): 67–81. doi: 10.26749/rstpp.141.1.67 . ISSN   0080-4703.