Wetland plants

Wetlands are defined by the presence of water – places where water covers the soil or where it is present at or near the surface for part of the year. That’s a wide-ranging definition, so it covers a wide range of wetland types and wetland habitats!

Wetlands are special places when it comes to vegetation. Many wetland species throughout Aotearoa are endemic and range from the tiny swamp helmet orchid (Corybas carsei) that is only found in the Waikato’s Whangamarino Wetland to Aotearoa’s tallest tree – the kahikatea (white pine, Dacrycarpus dacrydioides).

Where particular plants live is determined by the amount of water that is present. Marshes and swamps usually have a gradient that moves from open water and saturated soils to drier upland soils. These are some zone characteristics:

• Aquatic – permanent open water that is usually more than 1 m deep. Plants like duckweed are submerged but with their flowering parts above water.
• Emergent – shallow water between 5 cm – 1 m deep. Plants like raupō (bulrush, Typha orientalis) or kuta (bamboo spike sedge, Eleocharis sphacelata) are partially submerged.
• Saturated – soils are saturated most of the year. Plants like harakeke (flax, Phormium tenax), tī kōuka (cabbage tree, Cordyline australis) and maire tawake (swamp maire, Syzygium maire) tolerate a mix of flooded and drier conditions.
• Moist – soils are saturated at times but dry in summer. These conditions support trees such as kahikatea, mānuka (tea-tree, Leptospermum scoparium) and whekī (rough tree fern, Dicksonia squarrosa).
• Mesic – upland soils that may be saturated for short periods but are generally dry and mark the transition from wetland to other types of habitat. These conditions support kōwhai (Sophora spp.), mamaku (black tree fern, Cyathea medullaris) and rimu (red pine, Dacrydium cupressinum).

Wetland plant adaptations

Wetland habitats present challenging conditions, so some plants have adaptations that help them survive. Wetland soils are saturated and become anaerobic – lacking in oxygen. Plants need oxygen for respiration. Rushes like wīwī, raupō and sedges like kuta have spongy tissues that form air channels inside of their stems. Known as aerenchyma, these channels move oxygen from the parts of the plant that are above water to the parts of the plant that are submerged. Pukatea (Laurelia novae-zelandiae) and swamp maire have special breathing roots called pneumatophores. These specialised roots stick out of the swampy soil and supply air to the submerged roots. Pukatea, swamp maire and kahikatea trees develop buttresses (flared trunks at the base of the tree) that support the trees in the swampy ground.

Many emergent wetland plants have elongated stems to ensure that a portion of the plant is above the water. This is important for both photosynthesis and reproduction.

Another challenging condition in some wetlands is access to nutrients. Bogs are nutrient poor, so carnivorous plants like sundews (wahu, Drosera spp.) and bladderworts (Utricularia australis) gain additional nutrients by capturing insects and other invertebrates.

Wetland (repo) plants and te ao Māori

Traditionally, repo were both grocery and hardware stores for Māori. Repo brimmed with food and sustenance (such as tuna, kōura and various berries and seeds), materials for housing (such as roofing and insulation) and plants for rongoā Māori to treat wounds and ailments.

Perhaps the one plant most symbolic of customary Māori life is harakeke. Harakeke is commonly found in wet areas throughout Aotearoa. Although it is no longer needed for creating the many items crucial for day-to-day living, harakeke still holds significant value in te ao Māori. Raranga (weaving) tikanga and techniques are being revived and are flourishing. Harakeke heals both the people through rongoā and the whenua through riparian restoration.

Kuta is another wetland plant that is highly valued as a weaving resource. Woven gently, the kuta stem holds air, which provides warmth and softness in the finished product. These properties were valued in sleeping mats and as wall insulation for buildings.

There is significant mātauranga associated with the nurturing, harvesting and preparation of harakeke and kuta. Kōrero with local kaumātua and other whānau about these practices, especially when considering wetland restoration.