Retrophyllum

Superregnum: Eukaryota
Regnum: Plantae
Divisio: Tracheophyta
Divisio: Pinophyta
Classis: Pinopsida
Ordo: Pinales

Familia: Podocarpaceae
Genus: Retrophyllum
Species: R. comptonii – R. filicifolium – R. minus – R. piresii – R. rospigliosii – R. vitiense
Name

Retrophyllum C.N.Page, Notes Roy. Bot. Gard. Edinburgh 45: 379 (1988 publ. 1989)

Type species: Retrophyllum vitiense (Seem.) C.N.Page, Notes Roy. Bot. Gard. Edinburgh 45: 380 (1988 publ. 1989)}}

References

Page, C.N. 1900. Notes from the Royal Botanic Garden, Edinburgh 45: 379.
Govaerts, R. et al. 2017. Retrophyllum in World Checklist of Selected Plant Families. The Board of Trustees of the Royal Botanic Gardens, Kew. Published online. Accessed: 2017 Feb. 10. Reference page.
International Plant Names Index. 2016. Retrophyllum. Published online. Accessed: Jan. 1 2016.
Mill, R.R. 2016. A monographic revision of Retrophyllum (Podocarpaceae). Edinburgh Journal of Botany 73(02): 171–261. DOI: 10.1017/S0960428616000081 Reference page. Note comb. nov. Retrophyllum filicifolium
Tropicos.org 2016. Retrophyllum. Missouri Botanical Garden. Published online. Accessed: 1 Jan. 2016.

Retrophyllum is a genus of conifers in the family Podocarpaceae.[2] It contains five generally recognized extant species with a disjunct distribution in the Southern Hemisphere, found in Papuasia and also in South America.[1][3][4] Retrophyllum are evergreen trees typically occurring in tropical rainforests and cloud forests.

Etymology

The name Retrophyllum is derived from the Latin retro, meaning "backward" or "reversed", and the Greek phyllos, meaning "leaf". The name refers to the unique phyllotaxis where the adaxial surfaces of the leaves face up on one side of the shoot and down on the other.[1]
Description
Leaves of R. minus showing the phyllotaxis. The leaves have their ventral sides up on the left and dorsal sides up on the right.

Retrophyllum are evergreen trees. They range in size from dwarfed to very large,[1] reaching heights in excess of 40 and potentially 60 meters.[5] Resin canals are found in both leaves and the seed cones.[1] The bark is usually smooth at first, becoming fissured or flaking with age.[1][5][6]

The leaves are generally flat with a decurrent base and a spreading blade, but leading and cone-bearing shoots may also have small appressed scale-like leaves.[1][5][6] The base phyllotaxis or leaf arrangement is spiral though the leaves usually form subopposite and nearly decussate pairs. The leaves of a lateral shoot are further twisted at their petioles to form two pectinate rows in a horizontal plane around the shoot.[1] The leaf petioles in Retrophyllum are uniquely twisted on the lateral shoots in opposite directions on each side of a shoot orienting the leaf blades with the adaxial or ventral surface upwards on one side of the shoot and the abaxial or dorsal surface upwards on the opposite side of the shoot.[1][6][5] The leaf blade varies in shape from lanceolate to narrowly ovate. The leaves have conspicuous midribs and are amphistomatic with stomata present on both sides.[1]

Retrophyllum are dioecious with male pollen cones and female seed cones on separate individual trees. The male pollen cones may be axillary or terminal and solitary or grouped. They have glabrous peduncles. A pollen cone consists of many spirally arranged microsporophylls each with two pollen sacs producing bisaccate pollen.[1]

The female seed cones develop from axillary buds. They are often solitary but may also be paired. The cones consist of several basal sterile cone scales and a single apical fertile scale. The basal scales are fused. The fertile scale has one seed producing ovule. The single seed of the cone is covered by a modified ovuliferous scale known as the epimatium. The epimatium becomes fleshy and drupe-like at maturity. It varies in shape from elliptic to ovoid or pyriform and may be red, violet or purplish brown in color.[1]
Distribution

Retrophyllum has a naturally disjunct distribution covering the Maluku Islands of Indonesia, New Guinea, New Britain and New Ireland in the Asia-Pacific region, Fiji, New Caledonia and Vanuatu in the Pacific and parts of Brazil, Colombia, Ecuador, Peru and Venezuela in South America.[1] The species Retrophyllum minus occurs in riparian and lacustrine habitats on ultramafic soils in New Caledonia.[7] The other species usually grow in tropical lowland or montane rainforests or cloud forests.[5][6][8]
Fossil record

Retrophyllum shoots have a distinctive morphology in which the leaves are in subopposite pairs,[1] and twisted in such a way that the abaxial surface of one leaf is up, and in the other it is down. This feature, added to a distinctive epidermal morphology means that well-preserved specimens can be easily identified in the fossil record. The fossil record shows that Retrophyllum was present in the Cenozoic of Argentina,[9] Australia[10] and New Zealand.[11][12] It is now extinct in those places.
Taxonomy
R. comptonii is native to New Caledonia.

In a 2009 book on conifers, Retrophyllum piresii was treated as conspecific with Retrophyllum rospigliosii. The author stated "One specimen from low elevations in Brazil was separated as a distinct species, but it falls well within the range of variation of the species as a whole and is geographically close to some locations in Peru."
Species

There are five generally recognized species.[1][3]

Image	Scientific name	Distribution
	Retrophyllum comptonii (J.Buchholz) C.N.Page	New Caledonia
	Retrophyllum minus (Carrière) C.N.Page	Plaine des Lacs in New Caledonia
	Retrophyllum piresii (Silba) C.N.Page	Serra dos Pacaás Novos in Rondônia State in W Brazil.
	Retrophyllum rospigliosii (Pilg.) C.N.Page	Colombia, Venezuela, Peru, Ecuador, Brazil.
	Retrophyllum vitiense (Seem.) C.N.Page	Maluku, New Guinea, Fiji, Bismarck Archipelago, Santa Cruz Islands.

References

Farjon, Aljos (2010). A Handbook of the World's Conifers. Leiden: Brill. p. 937. ISBN 9789004177185.
Christopher N. Page. 1990. "Podocarpaceae" pages 332-346. In: Klaus Kubitzki (general editor); Karl U. Kramer and Peter S. Green (volume editors) The Families and Genera of Vascular Plants volume I. Springer-Verlag: Berlin;Heidelberg, Germany. ISBN 978-0-387-51794-0
Kew World Checklist of Selected Plant Families
James E. Eckenwalder. 2009. Conifers of the World. Timber Press: Portland, OR, USA. ISBN 978-0-88192-974-4.
Farjon, Aljos (2010). A Handbook of the World's Conifers. p. 942.
Farjon, Aljos (2010). A Handbook of the World's Conifers. p. 941.
Farjon, Aljos (2010). A Handbook of the World's Conifers. p. 938.
Farjon, Aljos (2010). A Handbook of the World's Conifers. p. 943.
Wilf, P.; Johnson, K.R.; Cúneo, N.R.; Smith, M.E.; Singer, B.S.; Gandolfo, M.A. (2005). "Eocene Plant Diversity at Laguna del Hunco and Río Pichileufú, Patagonia, Argentina". The American Naturalist. 165 (6): 634–650. doi:10.1086/430055. PMID 15937744. Retrieved 2019-02-22.
Hill, R.S. and Pole, M.S., 1992. Leaf and Shoot Morphology of Extant Afrocarpus, Nageia and Retrophyllum (Podocarpaceae) Species, and Species with similar Leaf Arrangement from Tertiary sediments in Australasia. Australian Systematic Botany.
Pole, M.S., 1992. Early Miocene flora of the Manuherikia Group, New Zealand. 2. Conifer. Journal of the Royal Society of New Zealand, 22: 287-302.
Pole, M.S., 1997. Miocene conifers from the Manuherikia Group, New Zealand. Journal of the Royal Society of New Zealand, 27: 355-370.