Proto Central Eastern Polynesian: *Mānawa
REFLEXES IN CONTEMPORARY POLYNESIAN LANGUAGES:
Hawaiian: Mānawa (Vitex rotundifolia "Beach vitex", Lamiaceae)
Māori: Mānawa (Avicennia marina s. australasica, "Mangrove", Acanthaceae)

ALTERNATIVE NAMES
Hawaiian: kolokolo kahakai, hina kolo (Vitex rotundifolia).
Māori: paetai, waikure (Avicennia marina s. australasica). The sprouting seeds are known as piaka.

Introduction
Mānawa in Hawai'i
Mānawa in Aotearoa
Gallery

This is another of the plant names, like māhoe, now shared exclusively by Hawaiian and Māori. It was probably originally a term for plants that had a role in protecting the shoreline from erosion that developed in Tahiti before the voyagers to Aotearoa and Hawai'i went their separate ways. Hawai'i (like the rest of East Polynesia except Aotearoa) has no native mangroves. The two species that have established themselves there now were 20th century introductions (others are also cultivated but have not yet become naturalized). The cosmopolitan large-leaved mangrove, Bruguiera gymnorrhiza, grows naturally from Maritius to Southeast Asia, China and Japan, Australia and the Western Pacific as far as Tonga and Sāmoa. The West Polynesian name is tongo (togo in Samoan orthography), from Proto Malayo-Polynesian *tengeR. This was introduced into Hawai'i in 1922 by the Hawaiian Sugar Planters Association, and had become naturalized by 1932. The other, the American red mangrove, was introduced by the American Sugar Company in 1902 to hold soil on the mud flats on Moloka'i (Wagner et al., Manual, pp. 1099-1100). The large-leaved mangrove grows up to 36 m. tall, a giant compared with its counterpart in Aotearoa, and probably too distant a memory by the time the explorers left Tahiti on the last stage of their journey. The red-leaved mangrove, Rhizophora mangle, grows to about 10 m., with distinctve prop roots supporting the slender trunks.

Mānawa in Hawai'i

The Hawaiian Manawa is a recumbent shrub often rooting at the nodes, with single plants forming mats several metres in diameter in favourable environments. Side branches are produced from the prostrate stems, rising from about 10 to 30 cm long. The rounded leaves are up to 6.5 cm long by 4.5 cm wide, usually single but sometimes in clusters of three. They are aromatic when crushed, with a scent reminiscent of sage.

Mānawa in Aotearoa

In Aotearoa the mānawa stretches from the shoreline into the water along the foreshore. The New Zealand mangrove, Avicennia marina s. australasica, is also found in Indonesia, West Malaysia, New Guinea, Eastern Australia, and New Caledonia. Like the kauri it is found naturally in New Zealand only north of latitude 38 degrees South, with its southern limits at Opotiki in the East and Kawhia in the West.

Leonard Cockayne (1855-1934), one of New Zealand's pioneer botanists and ecologists, regarded the mānawa as "one of the natural wonders of New Zealand" and "one of the most noteworthy plants in nature" (NZ Plants and Their Story, p.58). The plant has made some striking adaptations to enable it to flourish at the intersection of the land and the sea. It defines the margins of tidal creeks, and stabilizes the edges of estuarine channels. The mangrove's anchoring roots spread widely, and produce a large number of breathing roots, pneumataphores. Roots generally grow downwards, but the pneumataphores are erect. They are in the open air at low tide, absorbing the oxygen denied to the submerged roots on the mudflats. Barnacles and oysters attach themselves to the pneumataphores. These in turn provide food for fish like snapper which cruise the tidal creeks and channels feeding among the mangroves when the tide is right. The fibrous roots of the mānawa below the surface provide residences for crabs, with eels also making holes in among them. The trees have also developed ways to counter the adverse effects of salt when they absorb water for growth.

As well as enabling the plant to absorb oxygen, the pneumataphores retain the silt washed down from upstream on the adjacent coast and so eventually build up the shoreline, something accellerated by the widespread logging and erosion from changing land use in the last two centuries. This has given the mangroves a bad name in some localities, as they are seen as invading the harbour, although it is the ecological damage which has facilitated this. Another casualty has been the rimurehia or "eel grass", which provides an important haven for small fish and other sea creatures. It grows in cleaner sandy-bottomed shallow coastal water, but may be overwhelmed by the mānawa as this starts to silt up.

The shrubs have stout, spreading branches, with grey, furrowed bark. In the Bay of Islands and Hokianga they be trees up to 8 m. tall, but further south they are generally much smaller shrubs. The leaves of the mānawa are 5-8 cm long, oblong, and leathery, smooth above with a white or buff tomentum below. Apart from their normal role in photosynthesis, the leaves also excrete excess salt stored by the tree. The brownish-yellow flowers are borne in panicles, and are rich in nectar. They produce an ovoid 2 cm capsule from which a seedling appears complete with emerging roots before the fruit falls from the tree (as in the seedling pictured on the left). Some of the tropical mangroves produce seedings with a long anchoring root (there are photographs of these in the gallery), but the mānawa will be anchored by its regular roots which quickly develop and take hold when the seed is washed up in a suitable environment. This enables the mānawa to colonize quite extensive swatches of coastline and the peripheries of estuaries. once they have been shed from the trees, the seeds do not remain viable for long (probably not more than about 5 days, although they will look as if they are healthy much longer) so the combination of winds and currents rather than climate per se may account for their limited natural distribution in Aotearoa, and also for the genetic differences which have been observed between east and west coast populations. The ratio of mud to sand in their growing environment (the sandier the substrate the shorter the plants are likely to be) may also have much more to do with the size of the trees than other climatic factors (W.P & P.J. de Lange, "An appraisal of factors controlling the latitudinal distribution of mangrove ...", 1994). This species and its close relatives are the mangroves best equipped to cope with differences in the salinity of the water, with both the ability to resist the ill-effects of salt and also the ability to store surplus salt without damage to the plant (Robert et al. 2009), which also accounts in part for their wide distribution.

In other parts of its range the resinous wood of Avicennia marina has been employed for a variety of purposes, from construction to firewood (with the smouldering wood producing mosquito-repellent smoke); medicinal applications have also been found for various parts of the plant. However, the mānawa does not seem to have been put to any widespread practical uses in Aotearoa. This may be because of its limited distribution and the availability of many alternative resources.

Although this is very much a plant of the shore margin and intertidal zone, the NZPCN fact sheet on this species has this information about growing it outside its regular habitat:

Easily grown from ripe fruit which is usually partially germinated when it falls from the tree. Can be grown in normal potting mix but does best immersed in soil within brackish water. Avicennia can be easily translocated and as such has been moved in New Zealand by people outside its natural range. Although it is frost tender, once established plants are capable of tolerating much heavier frosts than has been assumed in the literature (see comments by de Lange & de Lange 1994).

Gallery