''Diselma archeri'' (dwarf pine or Cheshunt pine) is a species of plant of the family

Cupressaceae 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, subdio ...

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 Lake St. Clair (french: Lac Sainte-Claire) is a freshwater lake that lies between the Canadian province of Ontario and the U.S. state of Michigan. It was named in 1679 by French Catholic explorers after Saint Clare of Assisi, on whose feast day ...

. 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''.

Appearance and ecology

''Diselma archeri'' is a compact, prostrate

shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

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 A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...

(2–3 mm) are overlapping and arranged in

opposite decussate Decussation is used in biological contexts to describe a crossing (due to the shape of the Roman numeral for ten, an uppercase 'X' (), ). In Latin anatomical terms, the form is used, e.g. . Similarly, the anatomical term chiasma is named af ...

pairs which are pressed close to the stem. The square leaf arrangement is similar to that of '' Microcachrys tetragona'' ( Podocarpaceae) (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 Podocarpaceae. 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 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 Dioecy (; ; adj. dioecious , ) is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly (in animals) or indirectly (in seed plants). Dioecious reproductio ...

, where male and female cones are located on separate individuals. Both types of cones 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 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 Conifers are a group of cone-bearing seed plants, a subset of gymnosperms. Scientifically, they make up the division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single extant class, Pinopsida. All extant ...

heath and montane 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'', another monotypic genus in the subfamily Callitroideae, the Southern Hemisphere clade of

. Fossils of both ''Diselma'' and ''Fitzroya'' have been recorded in Tasmania. This evidence indicates that ''Diselma archeri'' is most likely a paleoendemic 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 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