PALMIET

Palmiet (Prionium serratum) is a robust plant that plays an important role in a large part of the Western Cape river ecosystems (www.plantzafrica.com). This fast growing plant can cover vast water areas. Under such conditions, it contributes to the purification of the water and plays an important role in stabilizing riverbeds and riverbanks from erosion.

Taxonomy

The species is the only representative of the family Prionaceae, thus an example of a monospecific family. This family belongs to the order Juncales and is closely related to the Juncaceae. The name 'wilde palmit' was already used before the 1700's by Van Riebeeck and later recorded by Thunberg in the second half of the 18th century. The English and Afrikaans names (palmiet and wilde palmiet) are similar. In Xhosa the species is called iNtsikane. The name Prionium is derived from the Greek 'prion' meaning 'saw' and refers to the leaf blades. The epitheton serratum refers to the toothed margins of the leaves.

Species biology

This semi-aquatic species is found in marshy areas, streams, rivers and riverbanks, often in large dense stands, as mentioned before. The plants grow up to about 2 m. The main stem is 5-10 cm in diameter and is usually covered with the dark brown, fibrous remains of old leaves. The lanceolate leaves are stiff, leathery and pale grey-green, with toothed margins. They are arranged spirally around the stem. The small flowers form a branched inflorescence that reaches to about half a meter. They are brown and occur from September to February. The young flower shoots (broken off before flowering) are eaten as a vegetable. The leaves are used for basketry work, hats and mats.

Distribution

Palmiet is an endemic species of South Africa, where it can be found from the Western Cape to the south of KwaZulu-Natal (Goldblatt & Manning 2000). Due to medicinal harvesting and as a result of degradation of habitat from overgrazing, clearing and frequent fires, the species and its wetlands are declining. In the Baviaanskloof Mega Reserve, the species has its main occurrences in the Kromme Rivier.

Conservation issues

Due to food harvesting and as a result of degradation of habitat from overgrazing, mechanical river alterations with heavy machinery and frequent fires, palmiet and its wetlands are declining. The decline of indigenous wetlands can be catastrophic. Wetlands play an integral role in the hydrologic cycle and provide important ecosystem services, including flood storage, water quality enhancement and/or amelioration, wildlife habitat, and buffering the effect of high water flows. Moreover, wetlands play an important role in the global carbon cycle (through the accumulation of peat), and as such wetland restoration can help to increase carbon sequestration and mitigate greenhouse gas emissions. In fact, wetlands are the largest global soil carbon reservoir, comprising around 8% of the earth’s land area, but storing almost 33% of the world’s soil organic matter. (Peatlands contain nearly 30% of all carbon on the land, while only covering 3% of the area (CC-GAP 2005)) The prevailing anaerobic (low to zero oxygen) conditions enhance the carbon storage capacity. Carbon is stored in wetland trees and other plants, as well as in plant litter, peat, soil and sediment which can be built up over thousands of years.

Research provides proof of the value of these services, but there is an on-going debate. Sceptics state that the creation of wetland will increase evapotranspiration, reduce water availability (since plants use water as well), whereas the decay of organic matter make wetlands a net source of greenhouse gasses. With regard to carbon, however, this only seems to be true when wetlands are drained or exposed to oxygen. In the case of water and flood control, it is nevertheless quite well understood that palmiet wetlands increase shear stress during floods, lowering the energy level of passing water. It is believed that palmiet has the ability to reduce photosynthesis during dry periods, reducing evaporation thanks to sunken stomata and a thick cuticle that are seen as adaptations to dry climates (personal communication Rebelo).