Wetlands at
Nā Pōhaku o Hauwahine Restoration Project

`Ahahui Mālama I Ka Lōkahi & Kawai Nui Heritage Foundation
with support from the Kailua Bay Advisory Council (KBAC)

Wetland Plants

The following is a discussion of wetland plants growing naturally or planted in the marsh and marsh border at the base of Nā Pōhaku o Hauwahine. Experience at this location with encouraging Hawai`i native plants (indigenous or endemic species) and discouraging introduced or alien plans (naturalized species) is the focus of the text. Species are listed roughly in order of abundance, beginning with the most abundant types, and reflecting conditions in the wet season of 2001. That is, an abundance reflecting both the assemblage occupying the natural marsh in this area as well as the maintained restoration area. At the bottom are those plants either brought in to populate the wetland or that appear naturally, but which generally do not do well at this location. A listing of aquatic animals for this location is given elsewhere, as are discussions of the vegetation and terrestrial animals of Kawai Nui Marsh generally. A listing of native plants (mostly non-wetland) from the same area, with photographs of these in flower, is provided by ‘Ahahui Mālama i ka Lōkahi.

Para grass, Brachiaria mutica (POACEAE)

    An introduced and widespread pest species in wet areas in the tropics, California or para grass is a large grass with a spreading habit. Although not really aquatic, the long stems grow horizontally as much as 6 m (20 ft) out from the shore of ponds and wet areas, eventually covering the surface and obscuring open water. California grass will grow to a height of several feet (about 1 m), or higher if supported by other vegetation. This species is a dominant form in much of Kawai Nui marsh. Maintaining pond habitat at Nā Pōhaku o Hauwahine requires clearing all California grass, usually with weed-wackers and herbicide, followed by hand removal of occasional seedlings, which are easily identified by their rapid growth and hairy stems (compared with other grasses that volunteer in this area). This level of control is effective.

Common cattail, Typha latifolia L. (TYPHACEAE)

    Cattails have tall stems with gray-green, strap-like leaves arising from the base and are distinguished by flower spikes at the end of the stems that mature and persists as dark brown "bobs." The green part of the plant grows up from a creeping, underground stem called a rhizome. These rhizomes are well established in the mat below Na Pohaku o Hauwahine, requiring some control (presently, cutting or pulling, and herbicide treatment) to keep this introduced species from dominating the landscape. Herbicide (Rodeo) is not particularly effective because the stem can remain viable underground; cutting provides only short-term clearance. Wetland habitat enhancement efforts at Na Pohaku would seem to encourage the growth of cattails, which are persistent colonizers of wet mud areas. Most effective at reducing colonization is to minimize exposed wet mud surfaces. The wind-born seeds do not germinate if landed on open water or a surface dominated by ground covers such as `ae`ae (Bacopa). Hand removal of the distinctive seedlings is effective at controlling future growth in areas of established native vegetation.

`Ae`ae, water hyssop, Bacopa monnieri L. Wettst. (SCROPHULARIACEAE)

    A low-growing (creeping) succulent plant, bright green in color with white to pale lilac, 5-petal flowers. Water hyssop forms mats on wet ground or floating out across a water surface, the stems rooting regularly at the nodes. This indigenous species is typically found in lowland wetlands. Two "mats" transferred from elsewhere in Kawai Nui in May 2000 soon spread and now form a nearly continuous ground cover over large areas of cleared marsh border. This species spreads and seeds readily on pond margins, and is now the most abundant plant in the wetland restoration area. The dense, spreading growth tends to exclude seeding by other species. With some minimal maintenance to remove occasional seedlings of para grass and cattails, only dayflower (Commelina) is effective at invading established Bacopa beds.

Honohono wai, dayflower, Commelina diffusa N. L. Burm. (COMMELINACEAE)

    This wetland plant typically consists of short erect to prostrate growing stems with roots forming at the nodes, alternate, pointed leaves, and small, bright blue flowers. This is a naturalized species widespread in wet areas in Hawai`i. Honohono wai grows extensively on pond margins and well back into dry areas at Na Pohaku o Hauwahine if encouraged by rain during the wet season. It is generally difficult to control by hand weeding or cutting, because pulling the runners leaves nodes behind that quickly resprout. Persistent weeding in areas of established `ae`ae and herbicide sprays in pure honohono wai stands can eliminate growth of this species, which relies on vegetative growth to spread and dominate, rarely producing seedlings.

Pycreus polystachyos (Rottb.) P. Beauv.

    An indigenous sedge mostly under 1 foot tall. Having appeared sometime in late 2001 at the wetlands restoration site, this plant has since spread rapidly, producing large amounts of viable seeds.

Kamole or primrose willow, Ludwigia octovalvis (Jacq.) Raven (ONAGRACEAE)

    Thought to be a Polynesian introduction, this herbaceous plant with yellow, 4-petal flowers grows in wet places. The leaves are long and narrow, the fruit a long, ribbed capsule. It rapidly colonizes areas opened by weed-wacking and digging, although colonization is seasonal at Na Pohaku.

Makai, kaluha, Bulboschoenus maritimus (L.) Palla subsp. paludosus (A Nels.) T. Koyama (CYPERACEAE)

    This indigenous wetland bulrush is very distinctive with its multiple,full light brown flower heads and three-sided upright growth. This species is found typically in wetlands close to the sea. Three small plants were collected from a drainage ditch at Kapiolani Park and planted at Na Pohaku o Hauwahine in June 2000. The plants have been spreading rapidly, both by seed and runners, and new plants are quite large compared with the population in Waikiki. Growth is somewhat seasonal, with mature upright growth turning brown and production of new shoots curtailed during the colder months.

Seashore paspalum, saltgrass, Paspalum vaginatum Sw. (POACEAE)

    Low growing (usually under 25 cm or 1 foot), dark green grass found along the edges of coastal (brackish) wetlands. Although not a native species, this grass is naturalized throughout the Hawaiian Islands along the banks of estuaries and coastal ponds. Planted from cuttings along the inland edge of our created pond at Na Pohaku o Hauwahine in February 2000, this species initially spread rapidly. Growth around the ponds is encouraged to soften the borders and limit colonization by weedy species. Although spreading readily in the restoration area by runners and seed, seashore paspalum is out-competed by `ae`ae in most areas.

False daisy, Eclipta alba (L.) Hassk.

    Upright or sometimes spreading plant with narrow, gray-green leaves and small white, daisy-like flowers. This non-native wetland border species occasionally appears in abundance along pond margins. It is a favored food of our resident mallard duck.

Neke or swamp fern, Cyclosorus interruptus (THELYPTERIDACEAE)

    An indigenous fern with leathery green fronds that may exceed 1 m in length (smaller in the marsh), and have leaflets with coarse, saw-like edges. Although a terrestrial plant, neke is common in wet areas and the most abundant native plant in the vegetation-choked marsh near Na Pohaku o Hauwahine. However, this fern is not doing well around the man-made ponds and transplantings tend not to succeed.

Duckweed, Lemna perpusilla Torr. (LEMNACEAE)

    This plant consists of a small, bright-green leaf (3-6 mm long) floating on the water surface. A single, thin white root extends down from the underside. Probably an introduced species, duckweed has been in Hawai`i for over 100 years, and appeared on its own in the newly opened water at Na Pohaku o Hauwahine in late 1999 and had completely covered the water surface by February 2000. However, it disappears during summer low water and does not necessarily return each wet season with rising water level.

Makaloa, sedge, Cyperus laevigatus L. (CYPERACEAE)

    A single planting was made in January 2000 to test suitability of growing conditions. By April, this plant had spread and seeded. However,growth is weak, seedlings (transplanted or not) failed to thrive, and other wetland species have limited the spread of the sedge.

Water hyacinth, Eichhornia crassipes (Mart.) Solms (PONTEDERIACEAE)

    The water hyacinth is a floating plant distinguished by each leaf having an inflated petiole (leaf stem), forming an air-filled float. The leaves are arranged in a rosette, out of the base of which feathery roots extend down into the mud or water. Spreads by runners (stolons). Conspicuous violet flowers develop on a stalk rising up from the basal rosette. Small water hyacinth plants appear occasionally around the created ponds, presumably growing from seed. These have all been removed by hand. If allowed to become established, water hyacinth would eventually cover the water surface and damage the wetland.