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Thursday, November 28, 2013

River Cabbage (Platycarpha carlinoides)

Family Asteraceae
A very unusual, small plant which grows low on the ground and is a relatively unknown genus of three species endemic to southern Africa. The plants are unusual because the inflorescences occur in the crown of the plant, at the bases of the leaves.

The three species of Platycarpha are quite distinct but they are all perennial herbs with compressed stems and no aerial branches. The above-ground parts of the plants die back after the growing season and the size of re-emerging leaves and inflorescences are dependent on the age of the rootstock and the availability of moisture. This can result in extreme variability in the size of the plants, especially in P. carliniodes. This species has a cartwheel-like growth and the diameter of the plant can vary from around 100 mm to 400 mm.

P. glomerata has an erect growth form, up to 0.6 m tall, whereas P. parvifolia is creeping and often not higher than 60 mm. Leaves of all three species have a smooth green upper surface and white, woolly, lower surface. In P. glomerata, leaves have a glossy, deep green upper surface and are thistle-like and deeply toothed with soft spines on the tips. Leaves of P. carlinoides are also deeply toothed but those of P. parvifolia are only slightly toothed and neither of them has spines.

Inflorescence sizes are also variable and the largest are found in P. carlinoides (20-60 mm in diameter), followed by P. glomerata (30-50 mm) and P. parvifolia (15-35 mm). Inflorescences are composed of numerous flower heads with 3-5 light to dark purple 5-lobed tubular florets. Ray florets are absent. Flower colour fades with age to almost white. The pappus consists of 5-10 long narrow scales. Seeds are glabrous, obscurely ribbed, cylindrical or somewhat compressed.
Flowering times are distinctly different in the three species and reflect the rainfall patterns in the distribution areas. Platycarpha glomerata flowers from November to March; P. carlinoides from March to September and P. parvifolia from August to October.
 Derivation of names
Platycarpha is derived from the Greek platys, for broad, and carpa, for fruit, referring to the broad fruit of P. glomerata. The species name, parvifolia, is Latin, meaning with small leaves; referring to the distinctly smaller leaves of this species; glomerata means clustered in rounded heads, referring to the inflorescence; carlinoides is derived from Carlina, an European genus, and oides to indicate the resemblance in growth forms.
 Conservation status
Although there are often very few specimens in herbaria and little is known about the genus, none of the three species are threatened. Where they occur, one often finds large stands of plants that can measure several square metres.

The species of Platycarpha are geographically quite isolated.
  • P. carlinoides is the most widespread of the three species and occurs in Namibia, Botswana and Northern Cape between 700 and 1700 m. It prefers seasonally moist depressions and dry river courses.
  • P. glomerata occurs in the eastern part of the country in inland areas of KwaZulu-Natal and the Eastern Cape at elevations below 500 m. It is prevalent in rural areas, in disturbed areas and along dirt roads.
  • P. parvifolia occurs in the northeastern part of the country at altitudes of 1200-1500 m in the North-West Province, Mpumalanga and Free State. It is often found near dams and streams in short grassveld or on vegetated floodplains.
Platycarpha glomerata and P. parvifolia probably do not have special pollinators as a variety of insects such as butterflies, beetles, bees and flies were observed visiting the flowers.

However, in P. carlinoides the pollinators most frequently observed were large black ants with velvet-white abdomens. Seed dispersal is most probably by insects (particularly ants), water and wind.

Economic and cultural value
Platycarpha glomerata is believed to have some magical powers in KwaZulu-Natal. A concoction of the whole plant (called intelezi ) is sprinkled in the yard around a homestead to protect it against lightning strikes during a thunder storm.
In the garden
Plants of this genus will probably not make attractive garden subjects but to gardeners interested in curious plants, they may have some attraction. Very little is known about the cultivation although cultivation from seed should be fairly easy in the correct soil medium and moisture regime. In the wild, Platycarpha glomerata grows on poor, stony soils in moist humid areas, often in disturbed situations. P. carlinoides grows in sandy soil with fine silt, often in depressions occasionally filled with water. P. parvifolia grows in turf soil on floodplains in grassland.