rimu

''Dacrydium cupressinum'', commonly known as rimu, is a species of tree in the family Podocarpaceae. It is a dioecious evergreen conifer, reaching heights of up to , and can have a stout trunk up to in diameter. It is endemic to New Zealand; its range covers the North, South, and Stewart Islands, and it typically inhabits lowland to montane forests. ''D. cupressinum'' has an estimated lifespan of 600–800 years, although it may live as long as 1,200 years.

''D. cupressinum'' grows in an erect (sometimes forked), and usually a monopodial manner. ''D. cupressinum'' is a tall species emerging above the main canopy, usually at about in height. ''D. cupressinum'' was first described in 1786 by Daniel Solander and was later given a full description in 1803 by Aylmer Lambert. ''D. cupressinum''s fruits are consumed by various birds such as: bellbirds, kererū, and the tūī. Its fruits also provide an important source of food and vitamins for the endemic flightless parrot, the kākāpō, which will only mate during years of heavy fruiting. ''D. cupressinum'' serves as a host for numerous vascular epiphytes, which are plants that grow on other plants. ''D. cupressinum''s ovules are pollinated by the wind, and its seeds are later dispersed by gravity and frugivory.

In Māori culture, ''D. cupressinum'' is of great importance. ''D. cupressinum'' had several medicinal purposes for Māori, and the British missionary, Richard Taylor, described the fruit as "much prized" by the natives. In 1773, the British explorer, James Cook, brewed the first native beer at Tamatea / Dusky Sound, extracting the young tips of ''D. cupressinum''s branches, to create beer. ''D. cupressinum'' was once the most harvested timber in New Zealand, being used for: flooring, furniture-making, wagon building, and other uses, before protection from logging under law. ''D. cupressinum''s conservation status was assessed by the IUCN Red List in 2013 as "Least Concern", and its population trend was assessed as "Stable".

Description

''Dacrydium cupressinum'' (rimu) is a species of dioecious evergreen conifer in the family Podocarpaceae, reaching heights of usually up to , but may reach up to tall, and can have a stout trunk up to in diameter. ''D. cupressinum'' grows in an erect (sometimes forked), and usually a monopodial manner. Its trunk is usually smooth and cylindrical, fluted on older trees; particularly towards the base. Its bark is grey to dark-brown in colour, shedding in large, elongated, thick flakes. When the outer layers of bark flake off, a distinctive wavey pattern of parallel raised ridges is visible on the new bark beneath. These lines of ridges have been described as resembling the contour lines on a topographic map. Areas of bark between the ridges have lenticels, small pointed projections with porous tissue that allow air to penetrate the bark, providing oxygen to the cells of the tree beneath the bark. The wood is typically a dark-red colour. ''D. cupressinum'' exhibits a pyramidal shape in the early growth stages, and the crown of mature trees evolves into a domed shape, with the first-order branches spreading outwards or ascending. ''D. cupressinum'' has an estimated lifespan of 600–800 years, although it may live as long as 1,000–1,200 years as a theoretical limit, from specimens examined at the foothills of Mount Ruapehu.

''D. cupressinum'' is characterised by its drooping (bent downwards) and pendulous (hanging) foliage. Juvenile branches are numerous, slender, with pendulous branchlets. In adult specimens, the branches are fewer, spreading, and have slender, pendulous branchlets. ''D. cupressinum''s leaves differ in colour, from dark-green to bronze-green, red-green, or in some cases orange in colour, they are typically a yellowish-green colour and are keeled, incurved, about 4 mm long, and imbricated (or arranged in an overlapping pattern). Juvenile leaves measure 4–7–(10) millimetres in length and 0.5–1 mm in width, they are acute, linear (long and narrow) to subulate (slender), slightly curved, and subfalcate (vaguely sickle-shaped) in character. Subadult leaves are ascending, incurved, 4–6 mm long, and are rhomboid (diamond-shaped) in character. Adult leaves are similar, but they are appressed (flattened down), measuring 2–3 mm, rigid, and are triangular in character.

Like all conifers, ''D. cupressinum'' does not have flowers, but instead has cones ( strobili); with male and female examples first seen on subadult specimens. In male specimens, cones are solitary or paired, terminal, measuring 5–10 mm, and are oblong (rectangular) in character, producing yellow pollen. ''D. cupressinum''s ovules are solitary and positioned terminally on up-curved branchlets. Its receptacles form a fleshy cup that is red or deep-orange in colour and measures about 1–2 mm in length. Its pollen cones are found at the tips of branches and are oval to oblong in shape, measuring 7–10 mm long and 4 mm wide. Each microsporophyll has a pointed tip, is green in colour, and is 2–2.5 mm long. At its base, it holds two yellow pollen sacs.

Fruiting takes over a year to mature and often coincides with the presence of young female cones. Its fruits are most commonly seen between February and May. ''D. cupressinum'' is a morphologically distinctive species, although it is sometimes misidentified with the seedlings of '' Manoao colensoi'', which instead have glossier, coarser leaves. The seed cones grow at the ends of short, curved branchlets or on the sides, measuring about 6–10 mm long. The bracts attached are short and barely visible when the cone matures into a swollen, orange to red colour. ''D. Cupressinum''s seeds are ovoid, dark brown to black in colour, slightly flattened, are tiny at about 4–5 mm long, and they ripen to a glossy black colour. ''D. cupressinum'' has a diploid chromosome count of 20.

Phytochemistry

The foliage of ''D. cupressinum'' contains various sesquiterpenes, with their levels showing significant variation in specimens, which is similar to the differences observed in diterpene levels. There are twelve known sesquiterpenes in ''D. cupressinum'' that have been identified by a 1985 study, none of these show any structural similarity to lauren-1-ene. The distinctive diterpene lauren-1-ene has been identified only in the foliage of ''D. cupressinum'', however, the concentration of this compound, along with other diterpenes, which also shows significant variation between specimens.

''D. cupressinum'' contains high-levels of the unique sesquiterpene terpene compounds of 9-epi-β-caryophyllene. ''D. cupressinum'' also has a distinctive flavonoid glycoside profile; it possesses flavonol-3-O-rhamnoglucosides and also, to a lesser extent, 3-0-methyl-myricetin glycoside compounds.

Gallery

File:Rimu (Dacrydium cupressinum) foliage and branchlets.jpg, Its leaves differ in colour, but are typically greenish-yellow, they are typically imbricated, or arranged in an overlapping pattern., alt=An image of D. cupressinum's slender-like leaves and branchlets. The greenish-yellow leaves are linear-subulate and imbricated, meaning they are arranged in an overlapping pattern.
File:Dacrydium cupressinum (45986054132) (cropped).jpg, A mature specimen growing above the canopy in a forest in the West Coast Region of the South Island., alt=A mature, relatively large, D. cupressinum specimen rises above the canopy in a native New Zealand forest. A few dead or dying trees are also visible in the background, similarly above the canopy.
File:Dacrydium cupressinum bark.jpg, Its bark is dark-brown in colour, shedding in large, thick flakes, while the wood is a dark-red colour., alt=The bark of D. cupressinum, it is dark-brown in colour, shedding in large, thick flakes. A few species of fungi are also visible on the bark.
File:Dacrydium cupressinum male cones (cropped).jpg, Its strobili, also known as cones, are solitary or paired, terminal, and they are typically a red or a deep-orange colour., alt=An image of D. cupressinum's slender leaves and its strobili (also known as cones), which are solitary or paired, terminal, and typically a red or deep-orange in colour.

Taxonomy

''D. cupressinum'' was first described in 1786 by European naturalists Daniel Solander and Georg Forster, in their publication titled, ''De Plantis Esculentis Insularum Oceani Australis Commentatio Botanica''. The British botanist Aylmer Lambert provided a more comprehensive description in his 1803 work, ''A Description of the Genus Pinus''. The species was given the name ''Thalamia cupressina'' by Kurt Sprengel in an 1826 volume of '' Systema Vegetabilium'', an accepted synonym of the species. In 1855, French botanist Élie-Abel Carrière named the species ''Dacrydium cupressiforme'', in his work ''Traité Général des Conifères''. ''Dacrydium cupressiforme'' is also recognised as an accepted synonym. ''D. cupressinum'' is the type species of the genus ''Dacrydium''.

Evolution

A 1998 study on the phylogeny of the Podocarpaceae family examined the evolution of ''D. cupressinum'' and various other species. The research identified it as sister to a clade consisting of various other Podocarpaceae species, including members of the genus ''Dacrycarpus''. This discovery revealed that ''D. cupressinum'' shares a common biological ancestor with these species, while maintaining its evolutionary uniqueness. A 2020 study argued that the ''Dacrydium'' genus originated in New Caledonia, based on a historical biogeographic reconstruction. Despite this, macrofossil evidence "strongly supports" an Australasian origin, and another study argues that ''Dacrydium'' originated in Australasia during the Late Cretaceous epoch and dispersed into Southeast Asia in the Early Oligocene.

In 2021, several researchers investigated the role of plant evolution, analysing how ecological changes have shaped biodiversity and trait development over long timescales. In the study, they revealed that polyploidy, is a primary driver of microevolution in green-plants, but its broader impact on macroevolutionary diversification and phenotypic innovation remains uncertain. In the study, they produced an ancestral reconstruction of gymnosperms using RNA sequencing. ''D. cupressinum''s cladistic placement can be summarised in the phylogenetic tree at the right.

Etymology

The etymology (word origin) of ''D. cupressinum''s genus, ''Dacrydium'', originates from the Greek , which translates to 'tear drop', or simply 'tear'; which refers to drops of resin from the tree. The specific epithet (second part of the scientific name), , translates simply to 'cypress'; which refers to the tree's similarity with ''Cupressus'' species. ''D. cupressinum'' is commonly known as rimu and red pine.

Ecology

''D. cupressinum''s seeds are dispersed by gravity and by frugivory. These seeds are well-adapted to be dispersed by birds; primary dispersers of ''D. cupressinum''s seeds include: bellbirds (''Anthornis melanura''), kererū (''Hemiphaga novaeseelandiae''), and the tūī (''Prosthemadera novaeseelandiae''). Other birds, such as white-eyes (''Zosterops lateralis'') and house sparrows (''Passer domesticus''), also feed on the fruit's fleshy receptacles. ''D. cupressinum'' is known to be browsed by deer and possums, which browse seedlings and consume the foliage and the branchlets, respectively.
Excrements of the wētā (''Hemedeina thoracica'') are frequently found in seed traps, which could indicate that wētā consume the seeds of ''D. cupressinum''. Its seeds have been recorded being destroyed by chaffinches, mice, rats, and wētā. An increase in rat (''Rattus'') numbers takes place after a mast seed fall of ''Nothofagus'' species and ''D. cupressinum'' individuals.

''D. cupressinum''s fruits are an important food and vitamin resource for the endemic flightless parrot, the kākāpō (''Strigops habroptilus''), which feeds on them. The fruits are particularly high in calcium and vitamins; kākāpō may have adapted to survive despite prolonged periods of limited access to these resources. It is likely kākāpō seek out sources rich in these nutrients when their physiological needs are heightened, such as during reproduction in females or growth in chicks. The kākāpō will only mate during years of heavy fruiting.

Several species of insects have been recorded as feeding on the stems and leaves, including: stick insects, weevils, '' Pyrgotis'' species, and looper caterpillars, from '' Pseudocoremia fenerata''. Other wood-boring insects on ''D. cupressinum'' include: '' Ambeodontus tristis'', ''Calliprason pallidus'', '' Prionoplus reticularis'', '' Rhynchodes ursus'', and ''Platypus'' species. ''D. cupressinum'' also serves as a host for two beetle species, ''Euderia squamosa'' and ''Sommatidia antarctica'', both of which lay their eggs and feed on the tree. Despite these two beetles sharing similar life cycles, certain distinguishing features allow for the differentiation between their infestations and association with the tree. The larvae of '' Otiorhynchus sulcatus'', an introduced weevil, are known to have caused damage to seedling roots in nursery beds. ''D. cupressinum'' is one of the most flammable New Zealand tree species. It is likely ''D. cupressinum'' has not evolved to be resistible against fire or develop particular traits against flammability, as fire is uncommon in the communities where ''D. cupressinum'' grows.

Epiphytes

''D. cupressinum'' serves as a host for numerous vascular epiphytes, which are plants that grow on other plants. ''Metrosideros robusta'' is one of the most prominent species in the North Island and the northern South Island, in which it takes root in the tree, extending its roots downward to reach the ground. Over time, ''M. robusta'' can eventually replace its host as the original tree due to old age or suppression. The New Zealand naturalist Walter Oliver, conducted a study in 1930 of epiphyte and hemi-epiphyte relationships with ''D. cupressinum'' in Gollans Valley, near Wellington. Oliver documented eleven and twelve species in a sunny habitat and a shady habitat, respectively, as epiphytes on ''D. cupressinum''. He also mentioned that ''Nothopanax arboreum'', a hemi-epiphyte species, was common.

Fungi

The New Zealand mycologist, G. H. Cunningham, recorded thirty-eight species of Thelephoraceae and twenty-seven specimens of Polyporaceae as saprophytes on ''D. cupressinum''. The most common fungi associated with ''D. cupressinum'', according to a 2012 study in the '' New Zealand Journal of Botany'', are '' Armillaria novae-zelandiae'' and ''Ganoderma applanatum''. The fungi species that were recorded to a lesser extent included: '' Hypochnicium polonense'', '' Rigidoporus concrescens'', and '' Irpex'' species. ''Armillaria mellea'' is the only species of fungi known to be parasitic to ''D. cupressinum''. The mycorrhizal fungi nodules of ''Dacrydium'' are small, at about 0.5–0.7 mm in diameter.

Phenology

''D. cupressinum''s ovules are pollinated by the wind. ''D. cupressinum''s seeds typically remain dormant for at least 30 days, but sometimes much longer prior to germination.
A 1964 study estimated that a "mature vigorous" individual would possess about of ripe seeds and receptacles or of clean sound seed, producing about 200,000 seeds. ''D. cupressinum''s seeds ripen between March and May, about 15–18 months following pollination and are later dispersed for over 1–2 months, although infertile seeds may continue to be released for a significantly longer duration. ''D. cupressinum'' seedlings will not establish themselves where there is moderate to severe root competition and a moderately dense canopy because of under low light intensities.

''D. cupressinum'' is known for exhibiting mast seeding, and the unique periodicity of seedfall. In Pureora Forest, in the North Island, and Wanganui Forest, in the South Island, seedfall data shows clear yearly fluctuations in seed production in studied specimens, in 1988. A 1988 study proposes that a combination of low seed production and cool temperatures two years before, followed by warm temperatures during seedfall, are necessary but not solely responsible for triggering a mast year in the tree. The relationship between seed production in one year and conditions from two years earlier plays an important role.

The growth rates of ''D. cupressinum'' can vary significantly, especially in its early stages. Height growth often occurs at the expense of diameter growth, with saplings limited to in diameter reaching up to tall. In open conditions, annual increments can be in height and in diameter, but growth slows in shaded forest environments, with seedlings growing per year.

Distribution

''D. cupressinum'' is endemic to New Zealand, and is the country's most common conifer. Its range covers the North Island, South Island, and Stewart Island. In the South Island, it is uncommon or absent in parts of the eastern side of the island. On the Banks Peninsula, it is almost entirely extinct, with only a single natural specimen remaining. ''D. cupressinum'' was previously common around the town of Little River. In the South Island, ''D. cupressinum''s range predominantly covers the western side of the island, and it is largely not present in: Canterbury, Marlborough, Otago, and more generally, the inland South Island.

''D. cupressinum'' was likely naturally not present in only a few specific areas of the North Island prior to European colonisation, which included: Tongariro National Park, Kaingaroa Forest, and the southern parts of Hawke's Bay. On the eastern side of the South Island, its presence is scattered, particularly in the areas in between Blenheim and Waikouaiti. ''D. cupressinum'' does occur, however, in smaller groups, such as in Ashley Forest, the Hunters Hills, the Kaikōura Ranges, and only a few other locales.

Habitat

''D. cupressinum'' typically inhabits lowland to montane forests, and sometimes near subalpine scrubland. ''D. cupressinum'' is a dominant or codominant emergent tree in mixed conifer or conifer-angiosperm forests reaching elevations of up to above sea level. ''D. cupressinum'' is commonly associated with other conifers in its natural habitat, such as: kauri (''Agathis australis''), and tōtara (''Podocarpus totara''), as well as angiosperms, which could include: taraire ('' Beilschmiedia tarairi'') and various ''Metrosideros'' species. ''D. cupressinum'' has a very wide climatic range and can grow in most soil contents, but it will grow faster in more fertile soils.

Uses

''D. cupressinum'' has played a significant role in both the Māori and European cultures of New Zealand. In 1773, the British explorer, James Cook, brewed the first native beer at Tamatea / Dusky Sound, extracting the young tips of the branches of ''D. cupressinum'' to create what was known as "spruce beer". The British missionary, Richard Taylor, published a book on the cultural and natural history of New Zealand plants in 1848. Taylor described that ''D. cupressinum''s fruit was "much prized" by the natives and an infusion of the wood was used for crafting beer. He also described that resin from the tree was "very bitter", but edible.

''D. cupressinum'' also served as a significant source of timber in New Zealand, because the species was present throughout many lowland parts of the country.

In European culture

''D. cupressinum'' was valued for its use as timber. ''D. cupressinum'', also known as red pine, was once the most harvested timber in New Zealand, consisting of 58 percent of the country's total timber production between 1918 and 1930. Its timber has been used for furniture-making, and the interior panelling of trams and railway-cars. Its timber has also been used for other smaller miscellaneous purposes, such as: ceiling bases, coffins, and picture-frames.

The timber has a uniform texture; it is durable and resilient, making it easy to work with. In 1931, it was called the "most important softwood in New Zealand". The timber is frequently chosen for decorative purposes; the timber merges the qualities of a textured hardwood with the accessibility and moderate weight of a common softwood. ''D. cupressinum''s primary roles as a timber include it also being used for: fencing, flooring, furniture-making, wagon building, weatherboards, and joinery for dressing grades, as well as framing for building grades. The heartwood is durable above ground, but the sapwood is prone to decay in wet environments and vulnerable to ''Anobium punctatum'' and '' Ambeodontus tristis'' infestations.

In Māori culture

''D. cupressinum'' is of great importance to Māori. Its fruit is abundant during each fruiting season, and served as a significant food source to Māori. The timber of ''D. cupressinum'' was crafted into both war spears and hunting spears. To the Ngāpuhi people, the timber was used for canoe-making (or waka). ''D. cupressinum'' also possessed some medicinal purposes to Māori, such as, its gum (or sap) is very astringent and was used as a styptic to stop bleeding from wounds. Its bark was utilised for decoction to treat wounds, and the inner parts of the bark were crushed into a pulp to treat burns. Its leaves were used to treat sores. There are some other more names that Māori had for specific parts of the tree; for example, the tree's heartwood was known as: , , or . Its fruit was known as , and the seed inside the fruit was known as . Another name some Māori used for the tree was , which the ethnographer Elsdon Best documented was used by the Te Arawa tribe (or known as iwi in Māori).

Conservation

''D. cupressinum''s conservation status was assessed by the IUCN Red List in 2013 as "Least Concern", and its population trend was assessed as "Stable". Its assessment in the New Zealand Threat Classification System was evaluated in 2023 as "Not Threatened". Although previously harvested for timber, ''D. cupressinum'' is now protected from logging

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