About Plagianthus divaricatus J.R.Forst. & G.Forst.
Plagianthus divaricatus, commonly known as salt-marsh ribbonwood, is a bushy shrub endemic to New Zealand. It has thin, twiggy, intertwined stems that bear small clusters of narrow leaves, with divaricate branching growth, and can reach a maximum height of 3 meters. It can grow in an open, twiggy form, or a wiry, tightly knit form. Lateral branches extend outward from a stout main stem, forming divergent linear twigs. When viewed under magnification, twigs are covered in small star-shaped hairs. Leaves are small and narrow, measuring 5–20 mm long and 0.5–2 mm wide. In spring, it produces large numbers of small five-petaled flowers. Flowers are creamy white with purple-tinged edges, small and drooping, and only male flowers have a sweet scent. It produces small white fruit around 5 mm wide. It hybridizes with lowland ribbonwood (Plagianthus regius); the resulting hybrid is a tall, bushy deciduous shrub with grey-green leaves that are wider and flatter than the leaves of P. divaricatus. The Plagianthus genus contains only two species: P. regius and P. divaricatus, both endemic to New Zealand and the Chatham Islands. P. divaricatus occurs across New Zealand's North Island, South Island, Chatham Islands, and Stewart Island. It can be found on both the west and east coasts in sheltered coastal and estuarine areas, or inland off stony beaches, and is likely present as far south as Dusky Sound in Fiordland. Its habitat is primarily coastal environments, including coastal wetlands, sandy banks, and estuaries. It also grows inland along estuarine waterways and off stony beaches. It is predominantly a wetland plant, but can occasionally be found in upland areas. It is commonly found growing alongside Olearia solandri, Coprosma propinqua, and Muehlenbeckia complexa. Compared to other similar estuarine species, P. divaricatus germinates better in both lower and higher saline conditions. It is also a quite cold tolerant species. Diels proposed in 1897 that its divaricating growth form is an evolutionary adaptation of subtropical genera to the colder temperatures of glacial periods. The detailed life cycle of salt-marsh ribbonwood is mostly unknown. Most species in the Plagianthus genus are deciduous (meaning they shed leaves seasonally) and have a dioecious breeding system. Divaricating shrub species are often pollinated by unspecialized insects, and many exhibit heteroblasty, a trait common in the Plagianthus alliance where the juvenile leaf or growth form is retained in a mature plant. Some divaricating shrubs grow erect branches to indicate a transition from the juvenile to the adult life stage. Salt-marsh ribbonwood is a dicotyledonous plant, meaning it produces two seed leaves after germination. It produces inflorescences (clusters of multiple flowers) on a specific branch, with flowers arranged either solitarily or in cymes. Flowers develop in early spring, from September to October. Pollination is thought to occur via cross pollination: large numbers of moths visit the flowers of salt-marsh ribbonwood, and wind is also a likely pollination vector for this species that grows in exposed habitats.
