''Diselma archeri'' (dwarf pine or Cheshunt pine) is a

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...

of the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Cupressaceae and the sole species in the

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...

''Diselma''. It is endemic to the alpine regions of Tasmania's

southwest The points of the compass are a set of horizontal, radially arrayed compass directions (or azimuths) used in navigation and cartography. A compass rose is primarily composed of four cardinal directions—north, east, south, and west—each sepa ...

and Central Highlands, on the western coast ranges and Lake St. Clair. It is a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispe ...

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''.

Appearance and ecology

''Diselma archeri'' is a compact, prostrate shrub which commonly reaches 1–4 m in height but has been recorded to reach greater heights in subalpine rainforest zones. The foliage has a grey-green appearance with branchlets curving downward at their tips. Branches are short, ridged and very numerous. Branchlet foliage appears square in cross-section and scale-like leaves (2–3 mm) are overlapping and arranged in opposite decussate pairs which are pressed close to the stem. The square leaf arrangement is similar to that of '' Microcachrys tetragona'' (

Podocarpaceae Podocarpaceae is a large family of mainly Southern Hemisphere conifers, known in English as podocarps, comprising about 156 species of evergreen trees and shrubs.James E. Eckenwalder. 2009. ''Conifers of the World''. Portland, Oregon: Timber Pr ...

) (creeping pine) and the two species can easily be confused. However, ''M. tetragona'' lives up to its name and grows low to the ground, spreading out with only occasional erect branches. Another species which can be confused with ''Diselma'' is ''Phaerosphaera hookeriana'' (previously known as ''Microstrobos niphophilus'' ) which is in the family

. Both these species have a similar growth habit and distribution, however, the opposite pairs of leaves on ''D. archeri'' again make it distinguishable from the other species. Bark is rough and scaly and often weathered revealing a reddish-brown inner bark. Being a

gymnosperm The gymnosperms ( lit. revealed seeds) are a group of seed-producing plants that includes conifers, cycads, '' Ginkgo'', and gnetophytes, forming the clade Gymnospermae. The term ''gymnosperm'' comes from the composite word in el, γυμν ...

no flowers are produced, instead seed development occurs on the surface of the scale-like leaves which are modified to form cones (see image). ''Diselma archeri'' is a dioecious shrub, where male and female cones are located on separate individuals. Both types of

cones A cone is a three-dimensional geometric shape that tapers smoothly from a flat base (frequently, though not necessarily, circular) to a point called the apex or vertex. A cone is formed by a set of line segments, half-lines, or lines conn ...

are very small (3–4 mm) and occur at the branch tips. The female cone is composed of two pairs of opposite cone scales and only the upper pair of scales is fertile.Armin Jagel, Veit Dörken: ''Morphology and morphogenesis of the seed cones of the Cupressaceae - part III. Callitroideae''. Bulletin of the Cupressus Conservation Project, Bd. 4(3), 2015, S. 91–103
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At maturity up to four small winged seeds are produced which are wind dispersed. ''D. archeri'' seedlings are uncommon as the species often re-sprouts from roots and trunks buried in

peat Peat (), also known as turf (), is an accumulation of partially decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, moors, or muskegs. The peatland ecosystem covers and is the most efficient ...

soils.

Taxonomy

''Diselma'' : ''dis'' (meaning double) and ''selma'' (meaning upper) is a reference to either the two fertile scales in the female cone or the arrangement of the overlapping leaves in the opposite alternating pairs. ''archeri'' is named after botanical collector William Archer (1820-1874) who was also a Fellow of the Linnaean Society, an architect and Member of Parliament for Deloraine, Tasmania. This species is commonly known as dwarf pine in reference to its prostrate growth pattern or Cheshunt pine which is in reference to a property belonging to William Archer, although the species would not have occurred there. Diselma archeri distribution

Distribution

''Diselma archeri'' is endemic to Tasmania and is only found in high rainfall alpine and subalpine areas of the South West and Central Plateau of the state. Its altitudinal range varies from approximately 580-1400m above sea level. Like many Tasmanian conifers ''D. archeri'' is very fire sensitive and will only occur in fire free areas of alpine coniferous

heath A heath () is a shrubland habitat found mainly on free-draining infertile, acidic soils and characterised by open, low-growing woody vegetation. Moorland is generally related to high-ground heaths with—especially in Great Britain—a cooler a ...

and

montane Montane ecosystems are found on the slopes of mountains. The alpine climate in these regions strongly affects the ecosystem because temperatures fall as elevation increases, causing the ecosystem to stratify. This stratification is a crucial ...

rainforest. This species can form a small tree (3-4m) in closed rainforest at high altitude and some ecologists consider ''Diselma'' to be one of the seven genera which can be used as rainforest indicators in Tasmania. In more open coniferous heathland the Dwarf Pine grows more prostrate and only reaches approximately 1-2m in height.

Phylogeny

The closest relatives to ''Diselma'' appear to be the South American genus ''

Fitzroya ''Fitzroya'' is a monotypic genus in the cypress family. The single living species, ''Fitzroya cupressoides'', is a tall, long-lived conifer native to the Andes mountains and coastal of southern Chile, and only to the Andes mountains Argentina ...

'', another monotypic genus in the subfamily

Callitroideae Cupressaceae is a conifer family, the cypress family, with worldwide distribution. The family includes 27–30 genera (17 monotypic), which include the junipers and redwoods, with about 130–140 species in total. They are monoecious, subdioecio ...

, the Southern Hemisphere clade of Cupressaceae. Fossils of both ''Diselma'' and ''Fitzroya'' have been recorded in Tasmania. This evidence indicates that ''Diselma archeri'' is most likely a

paleoendemic Paleoendemism along with neoendemism is a possible subcategory of endemism. Paleoendemism refers to species that were formerly widespread but are now restricted to a smaller area. Neoendemism refers to species that have recently arisen, such as thro ...

and is the last remaining species in a genus that was once more extensive and has refuged to specific alpine zones due to changing climate.Jordan, G.J., Barnes, R. and Hill, R.S. 1995. An early to Middle

Pleistocene The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...

Flora of subalpine affinities in lowland Western Tasmania. Australian Journal of Botany. 43. 231-242

References

External links

Gymnosperm Database: ''Diselma archeri''
{{Taxonbar, from=Q133228 Cupressaceae Monotypic conifer genera Pinales of Australia Least concern flora of Australia Flora of Tasmania Endemic flora of Tasmania Taxa named by Joseph Dalton Hooker Dioecious plants