One of the vegetation types unique to the Nieuwoudtville area is the Nieuwoudtville Dolerite Renosterveld. It is one of the most interesting soil types in Nieuwoudtville.
This vegetation type is found on fertile, heavy red dolerite clay soils, and is dominated by annuals and geophytes with very few shrubs. To the uninformed these open dolerite plains may look somewhat drab, but they in fact contain a great diversity of bulbs and annuals.
The soils are derived from a Karoo dolerite sill, which gave rise to the north-south row of koppies. The soils are locally known as rooigrond (red soil) due to their high iron content, which rusts to give a deep red colour. The soil in some places is simply fine red clay, but in others it is quite stony. It is a fairly rich soil – neutral to alkaline.
The dolerite clays have the remarkable ability to swell when wet, becoming very glutinous. They shrink when dry, developing deep cracks that can shear the roots of shrubby plants in summer.
The cracks result in a self-mulching process in which topsoil falls into the cracks and subsoil moves to the surface. This phenomenon discourages shrubs from occupying these soils. Bulbs, however, such as Hesperantha vaginata and the fiery orange Bulbinella, can thrive here without competition.
These soils are called vertisols and are very fertile, but cultivation depletes the soil nutrients. A completely different and unique suite of plants grows on these soils.
The original vegetation probably contained a mixture of shrubs but much has been lost due to overgrazing and ploughing.
During the flowering season annuals and geophytes cover the ground in a rich carpet of colour. Here the famous red Bulbinella latifolia var. doleritica (rooikatstert), the large red-flowered Romulea monadelpha(karoo satynblom), yellow and chocolate Hesperantha vaginata (perdeblom) and the dull-coloured but highly fragrant Gladiolus scullyi are common.
Hesperantha vaginata (perdeblom)
Hesperantha vaginata (perdeblom) is an intriguingly coloured geophyte, 12 – 18 cm, with slightly fleshy, sword-shaped leaves. They have large yellow flowers often marked with brown, 25 – 35 mm across.
Their flowering time is usually from August to September and if weather permits they will open in the afternoon and give a beautiful display of colour. These intriguing plants only occur in heavy dolerite clay soils and are endemic to the area. They are pollinated by monkey beetles and the seed is set a few weeks later. This species is listed on the Red Data species list as near threatened.
Colchicum coloratum (red cup-and-saucer)
Colchicum coloratum (red cup-and-saucer) is a stemless geophyte, up to 5 cm. It has two lance-shaped leaves with minutely fringed, often undulating, margins. Their flowers are 10 – 20 mm across, enclosed in a pair of large reddish bracts which form a deep cup.
These plants have adapted to be pollinated by rodents, although birds are occasional pollinators. Their flowering time is usually from July to mid September. The red cup-and-saucer usually occurs in heavy, red clay soils in dolerite koppies.
Romulea monadelpha (karoosatynblom)
Romulea monadelpha (karoosatynblom) is a stemless geophyte, growing up to 10 cm, with a rounded corm at its base. It has several needle-like basal leaves.
The lovely large glossy red flowers (hence the common name satynblom), have black markings on the inside and anther filaments that are fused into a column.
Their flowering time is late July to October. The karoosatynblom is an endemic, occurring mostly in heavy dolerite clay soils and is listed on the Red Data species List.