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Plagianthus divaricatus or saltmarsh ribbonwood is a plant that is endemic to New Zealand. The Māori name is mākaka.

Description
Plagianthus divaricatus is an upright shrub with closely interwoven branches. The shrub is found in coastal environments in areas with salt swamp, sandy banks and throughout estuaries.

Salt marsh ribbonwood (Plagianthus divaricatus) can present as open and twiggy, or the opposite as wiry and tightly knit. Lateral branches reach outwards from a stout stem, forming divergent linear twigs. Saltmarsh ribbonwood produces linear-ovate leaves and dioecious, meaning another flower on a separate plant carries the male and female reproductive organs. The salt marsh flowers are pale yellow or white with purple edges, and the male flowers emit a sweet scent. Bark is described as dark brown and grooved. Leaves are presented in narrow clusters that are alternately distributed, with measurements up to 20 mm x 3-5 mm.

Salt marsh ribbonwood is a divaricate shrub species, meaning their branches diverge at a wide angle and is one of two species with morphological distinctions (size, shape, structure) that share characteristics that include being small-leaved with a wide-branching angle. The Plagianthus 'alliance' is a related group of genera that share the features of having unisexual flowers, partial seed abortion, a reduction or carpels and stipules, and a pinnate leaf venation.

Characteristics of divaricating shrubs are key for survival in exposed areas, hence saltmarsh ribbonwood inhabiting mainly coastal areas of New Zealand. Their roots often act as soil stabilisers in areas vulnerable to erosion

Life cycle/Phenology
The detailed life cycle of salt marsh ribbonwood is mostly unknown. Leaf phenology for the majority of species in Plaginathus are deciduous, meaning seasonal shedding of leaves, with a dioecious breeding system. Divaricating shrub species are often pollinated by unspecialized insects, and have been documented as exhibiting heteroblasty, a common occurrence in the Plagianthus alliance which means that the juvenile form is kept within a mature plant. Some divaricating shrubs grow erect branches as a signal that they have moved from a juvenile to an adult.

Saltmarsh ribbonwood is a dicotyledonous plant, meaning they produce two seed leaves upon germination. They produce several flowers, or a cluster named an inflorescence, on a specific branch. These flowers are produced in the early spring and between September and October. Flowers are often arranged in a solitary pattern or cyme. Pollination is likely to occur through cross pollination due to the heavy presence of moths interacting with saltmarsh ribbonwood flowers, and due to wind in the exposed habitats occupied by saltmarsh ribbonwood.

Natural global range
Although Plagianthus may have originated in Australia, P. divaricatus is endemic to New Zealand and is a resident native taxon with a large and stable population. To be endemic to a place means that the species does not naturally occur anywhere else. The genus Plagianthus, found only in Australia and New Zealand, is composed of fifteen tree and shrub species. Out of this fifteen, only two species exist in New Zealand, the tree species Plagianthus regius (Manatu/Ribbonwood) and Plagianthus divaricatus. Divarication has been noted as an adaption from its Australian ancestors. Possible explanations for this include climate influence, either in response to water scarcity, or resistance to frost or wind damage. This adaptation is globally rare but is exhibited in nearly 10% of New Zealand’s woody endemic species.

New Zealand range
North, South, Stewart, and Chatham Islands.

Habitat preferences
Saltmarsh ribbonwood favours areas of coastal turf, which are typically communities of herbs, grasses and sedges that dwell on exposed headlands. These plant species have a high tolerance towards salinity which is proven by their proximity to salty onshore winds and high water. Saltmarsh ribbonwood can be found in coastal and inland tidal river areas where there is a sandy or gravelly bank presence, or a marginal to salty swamp environment. Salt marsh ribbonwood has been documented in areas of Stewart Island and at Maungawhio Lagoon in Gisborne. Both locations have been recorded to have the plant species being on the edges of water.

Predators, Parasites, and Diseases
There is currently not an extensive record of the relationship between disease and salt marsh ribbonwood. However, species that dwell in coastal areas are vulnerable to invasive exotic species such as creeping bent (Agrostis stolonifera), mouse ear chickweed (Cerastium fontanum), Yorkshire fog (Holcus lanatus), cat’s ear (Hypochaeris radicata), buck's horn plantain (Plantago coronopus), procumbent pearlwort (Sagina procumbens), and several clovers and trefoils (Trifolium and Lotus spp.). Despite these threats, salt marsh ribbonwood is often a dominant species amongst the coastal community. Further threats to coastal turf species such as saltmarsh ribbonwood include trampling by grazing farm animals like cattle, sheep, and deer. As for most species, human interference from recreation or erosion are also common threats to survival.

Plant interactions
Saltmarsh ribbonwood is a host of lichens, including the At Risk – Naturally Uncommon species Teloschistes sieberianus, and two common species: Parmotrema reticulatum and Ramalina celastri. Plagianthus divaricatus has been recorded to grow alongside Muehlenbeckia australis (pohuehue), Rubus fruticosus (European blackberry), Pteridium esculentum (Bracken fern, rarauhe), Phormium tenax (Flax, harakeke), Cordyline australis (New Zealand cabbage tree, tī kouka), and Apodasmia similis (Oioi).

Herbivore species associated with Plagianthus divaricatus have been recorded on Landcare research and given a reliability score from a scale of 1-10 to indicate the level of evidence for the association.

The following received a 10 on this scale and are described as directly affecting the plants’ structure:
•Batrachomorphus adventitiosus Evans, 1966. Hemiptera: Cicadellidae. Sucking bug, plant hopper. Possibly breeding on shrubs. Biostatus: native

•Graphania scutata Meyrick, 1929. Lepidoptera: Noctuidae. Moth or Butterfly Moth, caterpillars feed on leaves of herbs and shrubs. Biostatus: endemic

•Harmologa oblongana Walker, 1863. Lepidoptera: Tortricidae. Moth or Butterfly Moth, caterpillars web together and feed on leaves. Biostatus: endemic

•Hoherius meinertzhageni Broun, 1880. Coleoptera: Anthribidae. Beetle, larvae tunnel in dead wood of Malvaceae shrubs and trees; adult guts contained fragments of higher plants and fungal spores. Biostatus: endemic

•Liothula omnivora Fereday, 1878. Lepidoptera: Psychidae. Moth or Butterfly Case Moth, caterpillar feeds on leaves of shrubs and trees. Biostatus: endemic

•Peristoreus australis Broun, 1921. Coleoptera: Curculionidae. Beetle weevil. Adults associated with small holes in leaves of P. regius larvae reared from male flower buds of P. divaricatus. Biostatus: endemic

•Pseudococcus hypergaeus Williams, 1985. Hemiptera: Pseudococcidae. Sucking bug, mealybug. May excrete honeydew. Lives on shrubs and trees = attracts other species. Biostatus: adventive

•Romna scotti White, 1878. Hemiptera: Miridae. (Mired) sucking bug. Breeds on Podocarpus species but may be predatory not plant feeding. Biostatus: endemic

•Scolypopa australis Walker, 1851. Hemiptera: Ricaniidae. Sucking bug/insect. Adults and nymphs feed on native and introduced plants, eggs are laid in soft woody tissues of some plants such as tendrils. Biostatus: adventive

•Stigmella aigialeia Donner & Wilkinson, 1989. Lepidoptera: Nepticulidae. Moth or Butterfly moth. Caterpillars make mines in leaves of Plagianthus divaricatus. Biostatus: endemic.

The following received a 9 on the scale:

•Chloroclystis inductata Walker, 1862. Lepidoptera: Geometridae. Moth or Butterfly Moth. Caterpillars feed on flowers. Biostatus: endemic

•Leucaspis sp. ‘Tahuna Torea’ Henderson, 2012. Hemiptera: Diaspididae. Sucking bug, scale insect/ Lives on stem of P. divaricata. Biostatus: endemic

•Pseudocoremia lactiflua Meyrick, 1912. Lepidoptera: Geometridae. Moth or Butterfly moth, caterpillars feed on leaves. Biostatus: endemic

•Salicicola maskelli Brittin, 1915. Hemiptera: Diaspididae. Sucking bug, scale insect. Biostatus: endemic.

Conservation history
Saltmarsh ribbonwood has been recorded as Not Threatened for the years 2004, 2009 and 2012. The lack of change within the conservation status may be credited to salt marsh ribbonwood having an isolated habitat, not commonly affected by humans.

Cultural uses
As the Indigenous People of New Zealand, Māori have their own names for species, and these titles are often recognised officially within New Zealand’s naming systems. In Te Reo Māori, saltmarsh ribbonwood is known as mākaka, houi and runa.