Roridula (; from Latin roridus "dewy") is a genus of evergreen, insect-trapping shrubs, with two species, of about 1.3–2 m (4.3–6.6 ft). It is the only genus in the family Roridulaceae. It has thin, woody, shyly branching, upright, initially brown, later grey stems, with lance- to awl-shaped leaves crowded at their tips. The star-symmetrical flowers consist from the outside in of five, green or reddish, free sepals, alternating with five white, pink or purple, free petals. Further to the middle and opposite the sepals are five stamens with the anthers initially kinked down. These suddenly flip up if the nectar-containing swelling at its base is being touched. The center of the flower is occupied by a superior ovary. The leaves and sepals carry many sticky tentacles of different sizes, that trap insects. Roridula does not break down the insect proteins, but bugs of the genus Pameridea prey on the trapped insects. These later deposit their feces on the leaves, which take up nutrients from the droppings. The species can be found in the Western Cape province of South Africa. They are commonly known as dewstick or fly bush in English and vlieëbos or vlieëbossie in Afrikaans.
Description
The two species in the genus Roridula are slender evergreen shrubs up to 1.3–2 m (4.3–6.6 ft) high. They grow from a taproot with few side roots. The perennial, upright, shyly branching stems are leafless, except near the top. The leaves are arranged alternately, crowded at the tip of the branches, almost as if in a rosette. The leaves are awl-shaped, lack both stipules and a leaf stalk, either with entire margins or with distanced line-shaped lobes. The leaves and calyx are set with different sizes stalked glands or tentacles that secrete a resin.
The 5-merous bisexual flowers are set with several in racemes amidst the crowded leaves at the tip of the branches. The free sepals and petals are well-developed and star-symmetrical. The broadly inverted egg-shaped petals are white, reddish pink or bright purple and are overlapping in a circle in the bud. Inside the petals are five stamens that sit opposite the sepals and below the ovary. The filaments are free, line-shaped, topped by anthers that are connected with the filament near their base. These anthers have two pollen-containing cavities that open inwards through four short slits near the top. The anthers are initially flipped downward on the outside. They are subtended by a swelling that contains a cavity that contains nectar. When the swelling is touched, the anther explosively swings up, releasing the pollen through the slits. The superior ovary in the center of the flower consists of three merged carpels, that together protect three cavities within which are one to four anatropous ovules each of which is covered by a single layer. The upright style tapers towards the top and carries a small globe-shaped stigma or expands towards the top into an inverted cone-shaped stigma, covered in small grains. The smooth, cartilaginous, dehiscent fruit opens with three valves. The small, dark reddish brown seeds are ellipsoid in shape either with a smoothed netted structure or angular with three sutures and with prominent warts or a honeycomb-like structure. Both species are diploids having six sets of homologue chromosomes (2n=12).
Differences between the species R. dentata can be distinguished by its larger habit of up to 2 m, the line-shaped lobes along its leaves and the umbel-like inflorescences, whereas R. gorgonias is smaller, up to 1.3 m (4.3 ft), has entire leaves and spike-like inflorescences.
Taxonomy Carl Linnaeus described Roridula in 1764. The name Roridula derives from roridus, a Latin word meaning "dewy", which refers to the fine drops of liquid on the tentacles that give the leaves a dewy appearance. Over time, different botanists have held different views on the affinities of the genus Roridula. Jules Émile Planchon thought it should be assigned to the Ochnaceae in 1848. George Bentham and Joseph Dalton Hooker, two of the nineteenth century's most influential British botanists however, included it in 1867 in the Droseraceae. In 1912, Johannes Gottfried Hallier regarded Roridula as a specialized member of the Clethraceae. Hutchinson in 1959, and Arthur Cronquist in 1981 included it in the Byblidaceae. Current insights in the relationships of the Roridulaceae, based on a 2015 DNA-analysis, are summarized in the following tree.
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