African Violets in the Wild - An Overview of the Genus Saintpaulia
by Johanna Kolehmainen, November 2009
History of discovery and ornamental use
The first known collection of Saintpaulia was by Sir John Kirk who was a British vice-consul in Zanzibar in 1880´s. He collected the plant from “The coast opposite Zanzibar” in 1884 and sent a specimen to Kew Botanic Gardens in England. Unfortunately, the specimen was so incomplete that it was left without further notice. In 1891, the plant was collected near Tanga and in the East Usambara Mts. by Baron Walter von Saint-Paul-Illaire, a Regional Commisioner in Tanga in the German East Africa (now Tanzania). The rumors tell that some German nuns had first brought the plants to him. Von Saint Paul sent the plants to his father in Germany who was by then the President of the German Dedrological Society. He again shared the plants with the Director of the Botanic Garden at Herrenhausen in Hannover, Hermann Wendland. In 1893, Wendland described the plant as belonging to a new genus, and named it after the von Saint Pauls (the father and son), who were responsible for its inroduction to into Europe. Wendland described the genus based on the plant material collected near Tanga and named the species Saintpaulia ionantha. “Ion” is Greek for violet, and Wendland proposed the German name “Usambara Veilchen” for the species. It was translated to “Usambara Violet”, but was later commonly substituted by “African violet”, which is now the well-known English name for Saintpaulia (Baatvik 1993).
In the same year the genus was described to science, von Saint Paul senior brought some plants to the International Horticultural Exhibition in Ghent, Belgium, where he sold the whole stock to the horticultural agency Ernst Benary in Erfurt. Benary immediately realized the potential value of Saintpaulia in the plant trade and already in 1894 his firm was selling seeds and whole plants of Saintpaulia (Baatvik 1993).
Since the 1890's, thousands of cultivated Saintpaulia varieties have been developed and they have considerable commercial value in world horticultural trade. They are now among the most common house plants in the world. Many people also grow Saintpaulia cultivars and even wild species as their hobby. The African violet enthusiasts have established their societies in many countries, the largest being the African Violet Society of America.
Classification of the species
Species of the genus Saintpaulia are tropical perennial herbs that belong to the family Gesneriaceae. This family also includes many other popular cultivated ornamentals such as Streptocarpus, Achimenes, Sinningia, Episcia and Columnea (Heywood 1996). The closest relative of Saintpaulia is the genus Streptocarpus (Möller and Cronk 1997a).
Classification of the Saintpaulia species has changed over the years. The classification has been based upon vegetative characters, mainly the habit and type and arrangement of hairs on the upper leaf surface (Darbyshire 2006, Burtt 1958). The most recent revision applied a broader species concept reducing the number of species from twenty to six (Darbyshire 2006). Even this classification has been partly challenged by a recent study which revealed genetic differentiation of certain populations in the East Usambara Mountains using genetic markers with higher resolution than the previous studies (Kolehmainen & Korpelainen 2008). In the Usambara Mountains and nearby areas the distinction of Saintpaulia species is particularly difficult due to the morphological and genetic similarity of the populations (or taxa) (Möller & Cronk 1997a, Burtt 1958).
Distribution and ecology
Saintpaulia species are forest plants in a limited area in Tanzania and Kenya, being mainly confined to the biologically rich forests of the Eastern Arc Mountains. The Eastern Arc mountain range starts from the Taita Hills in southern Kenya and ends in the Uzungwa Mountains in Tanzania (Eastwood et al. 1998). These mountains are geologically very old and influenced by moist Indian Ocean climate (Lovett 1990). Some Saintpaulia taxa also grow on the coastal plain between the Eastern Arc Mts. and the Indian Ocean. The genus has restricted habitat requirements, and the majority of the taxa have become rare, mainly because of the habitat degradation due to the decrease of forests (Eastwood et al. 1998). Individual species / taxa have a restricted distribution, many are endemic to one mountain or a particular locality, and populations are normally small and isolated (Johansson 1978, Eastwood et al. 1998).
All Saintpaulia species require shaded growing conditions. They are usually lithophytic, growing on gneiss or granite rocks or steep cliffs along rivers and brooks, or as ground herbs in the forest. They commonly grow on the shallow soils on rocks or in pockets of humus caught in rock outcrops. They have also been observed growing epiphytically on tree trunks. Those species found on the coastal plains are usually confined to limestone outcrops in small patches of remnant coastal rain forests or in steep limestone gorges along rivers, usually under deep shade of forest canopy (Johansson 1978, Mather 1989, Eastwood et al. 1998). The genus is sensitive to drought and competition from other plants so it normally occurs on substrates where few other plants are able to survive. The plants growing together with Saintpaulia include e.g. mosses, epiphytic and epilithic orchids like species of Polystachya and pteridophytes such as Asplenium, Adiantum and Loxogramme. Rhipsalis baccifera (J.S. Mill.) Stearn, Zamioculcas zamiifolia (Lodd.) Engl. and Peperomia spp. have also been reported to grow with Saintpaulia (Johansson 1978).
Saintpaulias reproduce both from seeds and vegetatively from leaf cuttings or from shoot parts. In the trailing taxa, vegetative reproduction is apparently common, because roots can be produced at nodes and, when the internodes decay the plant may split up into separate individuals (Burtt 1958, Kolehmainen, pers. obs.). Because of the vegetative reproduction there can be groups of genetically identical plants within a population.
Saintpaulia has a 'pollen flower' that attracts pollen collecting insects with its bright yellow anthers, which may also attract insects by deceit after the pollen has been shed (Richards 1997). According to Vogel (1978), Saintpaulia is a pollen flower of the 'Solanum type', which are strictly bee-pollinated flowers that never possessed a nectary or have rudimentary, non-functional nectaries. The flowers of Saintpaulia are odourless to human, except for S. difficilis (now classified as a subspecies of S. ionantha) which has a very faint odour (Kolehmainen, pers. obs.). Pollen is not shed spontaneously because the anthers are fused at the top. The pollen is released by vibratory movement of the pollinator that causes the opening of the anthers (Harrison et al. 1999, Heimala 2008, Martins 2008). The main pollinators of Saintpaulia are bees of the genus Amegilla (Roubik 1995, Martins 2005, 2008, Heimala 2008). Saintpaulia can produce seeds through both self- and cross-pollination. Plants originating from self-pollinated seeds may have reduced vigour compared to plants from cross-pollinated seeds due to inbreeding depression (Kolehmainen et al., in press).
There are no studies published about the dispersal ecology of Saintpaulia. Long-distance dispersal seems impossible, because the seeds are not small enough to be blown far by wind. On the other hand, being so small (less than 1 mm) and lacking in endosperm, the seeds are unlikely to be consumed by animals for endozoochorous transport. My hypothesis is that the dispersal method depends on the type of habitat. Along streams the seeds or entire seed pods can be washed by rain from the rock surfaces into the stream and transported by water for quite short distances. Other plant parts may also be transported this way. Dispersal by water is probably most efficient during the rainy season when water levels are at the highest and when heavy showers occur. Wind dispersal probably occurs on steep and rocky mountain slopes, where wind may blow the seeds from rock surfaces for some distance, mainly downwards the slope. Naturally, the seeds can also fall downwards due to gravity.
Conservation
Loss and degradation of natural forests threaten the survival of many Saintpaulia populations both in the lowlands and in the mountains. Generally, the lowland populations are more threatened because only few small fragments of natural forest exist on the coastal plain. An increase in light means a more severe exposure to drought during the dry season. In the more humid mountains, competition from other plants which are favoured by increasing light may also be a threat (Johansson 1978, Eastwood et al 1998, Clarke 1998).
Presumably, a majority of the Saintpaulia populations in the Eastern Arc Mountains are within conserved forests, but this does not mean that the populations are completely safe because even protected forests are threatened in many places due to encroachment by farmers, pit-sawyers and gold miners. These activities disturb or totally destroy forest vegetation. Uncontrolled fires also tend to escape into protected forests from surrounding farmlands. Sadly, the government forest department has too limited resources to eradicate these problems. To my knowledge, very few, if any, of the lowland Saintpaulia localities are in protected forests.
To prevent further loss of Saintpaulia populations in the wild, both in situ and ex situ conservation measures are needed. Priority of the in situ conservation work should be on the small populations and populations located outside of protected areas. The most threatened populations should be located, their viability and threats assessed, and back up material collected for ex situ storage. Genetic structure of the populations should be studied in order to be able to design the sampling of the plants for ex situ storage and to set priorities for in situ conservation. However, genetic analyses are expensive and therefore difficult to carry out when resources are scarce. In situ conservation and management measures have to be assessed case by case. To ensure sustainability of the in situ conservation efforts, local people and other stakeholders should be involved in the work.
Ex situ conservation is important especially for small populations which are susceptible to random events that can destroy the habitat. They may also not possess enough genetic variability to be viable in the long term, and / or may suffer from negative effects of inbreeding, i.e. breeding among relatives. Ex situ conservation methods for Saintpaulia include cultivation of whole plants in botanical gardens and possibly seed and tissue banking. Saintpaulia taxa are already well represented in botanical gardens and private collections, but the actual genetic diversity being conserved ex situ is too narrow because the collections are often composed of only a few accessions per taxon (Eastwood et al. 1998, Miranto 2005). Seed and tissue banking methods have not been developed for Saintpaulia, but such project is being planned (Valerie Pence, pers. com.).
The Plant Conservation and Propagation Unit of the East African Herbarium, National Museums of Kenya, has carried out special conservation activities by collecting seeds and whole plants of the Kenyan species. They have established ex situ collections as an insurance against the loss of genetic diversity and to provide material for the research and eventual re-introduction trials. They have also broadened the genetic base for re-introduction and translocations by cross-pollinating individuals from small populations (Simiyu et al. 1996). This kind of conservation measures should be initiated also in Tanzania to safeguard the survival of the most threatened Saintpaulia populations.
Tourism could, to some extent, contribute to the conservation of the African violet. The idea of using Saintpaulia as a tourist attractions has been suggested in many occasions (e.g. Mather 1989, EUCFP 1995, Simiyu et al.1996, Kolehmainen 2005) and the plant is already attracting some visitors to the Amani Nature Reserve in the East Usambara Mountains and to the Udzungwa Mountains National Park (TANAPA 2009). Moreover, the Magoroto Mlinga Community Ecotourism Project in the East Usambara Mountains (Kolehmainen et al. 2008) and the Saintpaulia Conservation Project in Kachororoni, Kenya (Tengeza & Githitho 2009) are currently developing Saintpaulia tourism. Because many plant enthusiasts are growing wild African violet species in their private collections, there is a potential market for special African violet tours to the wild habitats. Part of the revenues from such tourism should be channeled to the conservation of the genus and to development of local communities.
Literature cited
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