[3] Plagianthus divaricatus or salt-marsh ribbonwood is a bushy shrub endemic to New Zealand with thin twiggy intertwined stems that have small clusters of narrow leaves.
[1] Salt marsh ribbonwood (Plagianthus divaricatus) can present as open and twiggy, or the opposite as wiry and tightly knit.
Leaf phenology for the majority of species in Plaginathus are deciduous, meaning seasonal shedding of leaves,[7] 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.
It is found on both the west and east coasts in sheltered coastal and estuarine areas or inland off stony beaches.
[1] Plagianthus divaricatus is commonly found growing with; Olearia solandri, Coprosma propinqua and Muehlenbeckia complexa.
[10] Plagianthus divaricatus is also known to germinate better in lower and higher saline conditions compared to other similar estuarine species.
[11] It is also quite a cold tolerant species,[12] which could be due to its divaricating nature which Diels in 1897 proposed as an evolutionary adaptation of subtropical genera in response to the colder temperatures of the glacial periods.
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.).
[14] Further threats to coastal turf species such as saltmarsh ribbonwood include trampling by grazing farm animals like cattle, sheep, and deer.
[16] 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),[17] and Apodasmia similis (Oioi).
Eriophyes plaginus, also endemic to New Zealand, and also only present on both P. regius and P. divaricatus, causes deformities on the inflorescence and induces ‘witches' broom’ galls.
Caterpillars of Graphania scutata, Harmologa oblongana, Liothula omnivora (Case Moth), Pseudocoremia lactiflua and Stigmella aigialeia feed on the leaves of P.
[23] Thus, it is likely that P. divaricatus is similarly dispersed as it has small fleshy fruit like that of Coprosma and Muehlenbeckia, as well specifically being found in association with C. propinqua and M. complexa.
One theory for the high numbers of divaricating plants in New Zealand, a group which P. divaricatus belongs to, is as an ecological adaption for protection against moa browsing.
[24] Therefore, sometime in the past, one of the primary herbivores of P. divaricatus could have been moa resulting in the plant evolving this twiggy shrublike appearance.
[25] The lack of change within the conservation status may be credited to salt marsh ribbonwood having an isolated habitat, not commonly affected by humans.