Gramineae

Pipe grass

Bambusoideae; Oryzodae; Ehrharteae. There are 27 species of which 23 are indigenous to southern Africa of which all except 1 variety of 1 species is endemic.

The genus Ehrharta Thunb. is distributed within the cool temperate parts of southern Africa, south-western, southern and eastern Australia, Tasmania, New Zealand and Malaysia (Gibbs-Russell & Ellis 1987). In southern Africa Ehrharta can be divided into seven species groups: Setacea, Capensis, Erecta, Calycina, Ramosa, Dura and Villosa. Presently three taxa are assigned to the Villosa group: E. thunbergii Gibbs-Russell and E. villosa Schult. f. with two varieties, var. villosa and var. maxima Stapf. Ehrharta villosa is distributed along the southern coastal belt of South Africa between 33 and 35°S and 18 and 28°E (Gibbs-Russell et al. 1991). E. villosa var. maxima is less common in the western part of the distribution range (Gibbs-Russell 1987) but extends further east to Hamburg near East London than E. villosa var. villosa (Burns & Lubke 1986). The species is endemic to South Africa and populations are fairly rare, although local dominance may occur (Gibbs-Russell et al. 1991). In New Zealand Ehrharta villosa has been recorded at one site in the Koitiata dunes and adjacent pine plantations in Santoft Forest where it was planted as part of a sand stabilisation trial by the New Zealand Ministry of Works (Hoare et al. in prep.). It grows as a dense sward which appears to choke out other vegetation.

Ehrharta villosa Schult. f. is a robust perennial from long, creeping, naked, woody rhizomes, forming single, erect culms or small tufts (about 900 mm tall) where branching occurs from the base of the culm. Nodes are glabrous. The leaves are bluish-green, small and wiry, and reduced. Basal sheaths are loose, papery, grey or whitish. Leaf blades are deciduous or persistent, linear to 8 mm across, 15-130 mm long, not basally aggregated, rolled gradually and tapering at the tip. The inflorescence is an open raceme of hairy spikelets. In var. maxima the inflorescence is subtended by an inflated leaf sheath whereas in var. villosa the inflorescence is exserted from the uppermost leaf sheath. Spikelets in var. villosa are 11-14 mm and in var. maxima are 13-18 mm (Gibbs-Russell et al. 1991). The Villosa group is distinguished morphologically from the other species groups by the presence of large, profusely hairy, bearded and aristate spikelets and by a suffrutescent habit with reduced leaf blades and culms that are woody at the base (Gibbs-Russell 1987). All the taxa in the Villosa group are robust and possess long rhizomes. The closely related taxa in this group show a cline in size from the smaller, aristate forms of E. thunbergii in Namaqualand on the South African west coast, to the robust, sub-mucronate, dune-building E. villosa var. maxima. The other variety, E. villosa var. villosa has morphological and anatomical intermediates between these two taxa as well as to other species of Ehrharta (Gibbs-Russell 1987). The two varieties are sympatric throughout most of their distribution and intermediates between the two varieties are found (Gibbs-Russell 1987). E. villosa is distinguished from E. thunbergii by its naked rhizomes and longer spikelets and comparitively longer glumes. Some hybridisation occurs between the two species.

Used for dune stabilization.

The genus Ehrharta has a base chromosome number of 12 (Spies et al. 1989) and E. villosa var. villosa (the only taxon in the group to be studied successfully) had the highest ploidy in the genus with a base number of 60 (Spies et al. 1989). Despite the high ploidy no laggards were observed (Spies et al. 1989).

The leaves lack a midrib and all first-order vascular bundles are similar. These alternate with smaller vascular bundles. The epidermis in the leaves is relatively thick and covered with a waxy cuticle. Bulliform cells occur in the narrow furrows between adaxial ribs. Stomata are found on both leaf surfaces, although there are appreciably more in number in the abaxial than adaxial epidermis (Ellis 1987; Hoare 1994). Abaxial stomata are found in the intercostal zones, are well-sunken and are overlapped by four cuticular flanges which extend from the adjacent epidermal cells (Hoare 1994). Trichomes or prickles are present on the adaxial ridges (Ellis 1987). The internal anatomy of the leaves has some C3-C4 intermediate characteristics (Ellis 1987), but is more akin to a C3 arrangement: the mesophyll is semi-radiate in arrangement, although the abaxial chlorenchyma has a more palisade structure and there are few intercellular spaces in the mesophyll (Hoare 1994). The culm anatomy is dominated by a cortex of chlorenchyma and a parenchymatous pith. Sunken stomata are found in the thick cuticle adjacent to the regions of chlorenchyma and are attached to the epidermis by means of a schlerenchymatous girder.

None reported and considered to be non-toxic.

Ehrharta villosa occurs along the winter rainfall to transitional all-year to summer rainfall regions of the South African coastline and along those parts of the coast with a warm ocean current (Hoare et al. in prep.). The species is absent from the true summer rainfall regions, although these areas also coincide with warmer temperatures and higher rainfall. The climate is warm and temperate throughout the range of the species with annual rainfall varying from 600 to 1,000 mm per annum. It occurs in a number of habitats, including foredunes (dune hummocks and dune slacks), primary dunes (open scrub), rear dunes (dune thicket, forest, fynbos), blowout areas and stabilised dunes (Hoare et al. in prep.). It is absent from the shore zone, probably because of environmental constraints.
Ehrharta villosa may occur on foredunes as a pioneer stabilising sand to produce dune ridges or hummocks. Associated species in this habitat may be Scaevola plumierii, Arctotheca populifolia, Ipomoea brasiliensis, Cynanchum natalitium, Dasispermum suffruticosum, Gazania rigens, Tetragonia decumbens, Agropyron distachium or Ammophila arenaria (Hoare et al. in prep.). Ehrharta villosa typically has an aerial cover of between 1 and 40% in these habitats, where one species is usually locally dominant. Ehrharta villosa is not a common species in dune slacks, although the authors have observed it growing in association with species such as Sporobolus virginicus and Gazania rigens in dune slacks of the Alexandra region and on its own at other localities (Hoare et al. in prep.). The typical growth form of Ehrharta villosa in this habitat is a sparse series of long runners with no branching (Hoare et al. in prep.). In dune scrub Ehrharta villosa typically occurs along the dune slipfaces of the zone where it may be associated with the dwarf shrub Myrica cordifolia, but the grass is never a dominant species in this habitat. Ehrharta villosa is, however, a common pioneer of rear dunes (Lubke & Van Wijk 1988) and is an important binder of exposed sand landwards of the backshore (Tinley 1985). Few other foredune pioneers occur in this region of the coast. Similarly, populations of Ehrharta villosa may be common in dune blowouts (Lubke & Van Wijk 1988) in association with Helichrysum species and Senecio elegans, although it is primarily a secondary coloniser here.

Gas exchange and anatomical studies on E. villosa indicate that the species has a typical C3 photosynthetic type (Hoare et al. in prep.). Gas exchange studies on E. villosa indicate that the species has wide temperature optima from 22 - 27 °C as well as light optima from 800 - 1,600 µm^-2 s^-1 as well as quantum efficiencies that are high at low light intensities gradually reducing at higher light intensities (Hoare et al. in prep.). Above 27 °C and light intensities of 1,600 µm^-2 s^-1 water use efficiency and quantum efficiency drop and plants reduce stomatal conductance. These factors suggest that the species is adapted to mesic conditions, warm temperatures and a wide range of light intensities up to 1,600 µm^-2 s^-1 (Hoare et al. in prep.).

V_max is substantially higher than the maximum observed rate of photosynthesis indicating that there is significant mesophyll or stomatal resistance to gas exchange in the leaves of E. villosa (Hoare et al. in prep.). The value of g_s (Farquhar & Sharkey 1982) indicates relatively high stomatal limitation. These observations are consistent with a C₃ plant living in a water-limiting environment where stomatal control of water loss is important for the survival of the plant. No studies on nutrient relations have been undertaken but observations in the field indicate that E. villosa is healthiest where tidal deposition of organic material, especially from Zostera capensis, is highest leading to higher levels of soil organic content than more inland dune sites. This suggests that organic nutrients may be limiting in dune sites where E. villosa vigour is low (Hoare et al. in prep.).

Ehrharta villosa occurs in sandy soil at or near the coast (Chippendall 1955; Gibbs-Russell 1987, 1989; Acocks 1953; Bond & Goldblatt 1984) and is only one of two species of Ehrharta to grow in coastal dunes (Gibbs-Russell 1987). The South African dune sands are classified as littoral sands of the arenosol order of soils and geologically referred to as being quatrose, shelly, well-sorted sands (Tinley 1985). They have a structureless profile and high porosity and are, as a consequence, easily leached, have a low water-holding capacity and are typically poor in nutrients (Tinley 1985). The water content of dune sands where Ehrharta villosa occurs has been measured at between 2.3 and 4.4% with dune slacks having a higher value of 10.8% (Rothman 1992; Hoare 1994). The lack of humus in dune soils is also a feature with the only organic inputs being sea drift on the shoreline and plant litter in dune shrubland and thicket. Organic contents in dune soils where Ehrharta villosa occurs have been measured at 0.35% - 0.4% in dune slacks and up to 1.0% in the pioneer zone and on the edge of the secondary coloniser zone and 1.2% at the high tide mark (Rothman 1992; Hoare 1994). Sand movement generally decreases with distance inland so that Ehrharta villosa occurs in habitats with a range of sand movement regimes. However, senescence in populations of Ehrharta villosa have been observed in areas of the dune system where sand movement has been reduced. The soil pH of Ehrharta villosa habitats varies from 7.8-8.6 (Hoare 1994).

E. villosa transplants demonstrated the greatest amount of growth under conditions of low sand accretion, with 20 g.m^-3 accumulation of sand over 4 months leading to significant reduction in the height of experimental plants and 2,000 g.m^-3 leading to mortality (Hoare et al. in prep.). Salt accumulation also negatively affected experimental plants and natural populations of E. villosa tend to die back during the time of the year when strong onshore winds deposit high amounts of salt spray on the leaves of the plant, although root and rhizome growth during this period remains constant.

Culms of E. villosa become largely dormant during winter, although root and rhizome growth has been observed to continue during this period (Hoare et al. in prep.). Flowering occurs sporadically from September to March.

None known and plants appear to be healthy and free of disease throughout their range of habitats.

E. villosa plants to be small and leafy in the pioneer zone, growing taller with distance inland, but showing die-off at the back of the foredunes. The ratio of dead to living culms across this gradient rises from 0.09 to 1.61 demonstrating a definite trend of degeneration away from the primary zone of colonisation (Hoare et al. in prep.).

Australian Plant Name Index

NZERN - the New Zealand Ecological Restoration Network

HortNET

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