Selaginella is the only genus in the family Selaginellaceae. These plants belong to the lycopods, one of the groups previously referred to as fern allies. Selaginella is one of two groups of vascular plants that show heterospory – male (microspores) and female (megaspores) are produced in different sporangia and are of different sizes, the other being Isoëtes or quillworts.
Selaginella kraussiana is one of six to eight Selaginella species occurring in South Africa and is the only one regularly cultivated as an indoor or outdoor plant. The species is especially suited for cultivation in deeply shaded moist to wet areas.
Long-lived plants with a moderate growth rate. The plants grow on the soil, on rocks, and rarely also as low-level epiphytes . Stems herbaceous, prostrate on the soil surface forming loose mats, rooting at the branching points, the stems unequally branched, round or with shallow grooves, to 1 mm in diameter, glabrous.
Lycophylls (leaves) of two sizes, pale green, herbaceous to thinly herbaceous, spaced or overlapping; lateral lycophylls set at a narrow or broad angle to the stem, sessile, oblong-elliptic, to 3.2 mm long, to 1.5 mm wide, acute, the base unequal, the upper lobe the largest, entire to serrulate (minutely toothed), the vein raised on the upper surface and thickened towards the apex and ends short of the margin, the epidermal cells on the upper surface papillate; median lycophylls dorsally in 2 alternate ranks, sessile, lanceolate to ovate-lanceolate-aristate, to 2.6 mm long, to 1 mm wide, base unequal, curved towards the centre, the outer lycophyll lobe largest, entire to serrulate, the vein raised on the upper surface and thickened towards the apex. Ligules membranous, awl-shaped, to 0.4 mm long.
Strobili (cone-like structures containing reproductive organs) with lycophylls differing from the sterile lycophylls, sessile, solitary at the apex of secondary and lower order branches, to 17 mm long; sporophylls (leaf-like structures subtending the sporangia) similar, ephemeral, herbaceous, lanceolate to lanceolate-ovate, to 1.6 mm long, to 0.6 mm wide, keeled, serrulate. Sporangia (structures producing spores) subtended by a membranous awl-shaped ligule, to 0.2 mm long in axil of sporophylls, ovate, sessile, spheroidal to slightly dorsiventrally appressed, with 2 equal valves; megasporangia (producing female megaspores) borne basally in strobili, to 1 mm in diameter; microsporangia (producing male microspores) to 0.5 mm in diameter. Megaspores pale yellow, 4 per sporangium, globose, trilete, perispore cristate, reticulate, exospore (544–) 572 (–608) m m in diameter; microspores yellow, numerous, globose, trilete, echinate, the spine bases joined to form a reticulum of ridges, exospore (34–) 36 (–40) m m in diameter.
Selaginella kraussiana is relatively widespread in South Africa and is not considered threatened.
Distribution and habitat
Selaginella kraussiana occurs from the Tsitsikamma Forests in the southern Eastern Cape, along the higher rainfall and milder lower lying eastern parts of the Eastern Cape and KwaZulu-Natal to Swaziland, Mpumalanga and Limpopo. The species also occurs in tropical Central and East Africa as far north as Ethiopia. It also occurs in Bioko, Madeira and the Azores. The species has become naturalized at Hermanus and Betty's Bay.
The species occurs mostly along streambanks, moist cliffs, at waterfalls, and along forest margins, but frequently also on the forest floor away from water.
Derivation of name and historical aspects
Selaginella kraussiana is named after Christian Ferdinand von Krauss (9 July 1812–15 September 1914), who became Director of the Natural History Museum in Stuttgart in 1856. Krauss initially practiced as a pharmacist, but then studied mineralogy, zoology and chemistry. Krauss travelled and collected in South Africa from 7 May 1838 to 22 April 1840. Several South African plants species are named after Krauss. Kunze based S. kraussiana on one of the collections collected by Krauss during his sojourn from 2 June 1839 to 5 February 1840, in KwaZulu-Natal.
Selaginella is a genus of about 750 species, most of them occurring in the tropical parts of the world, but a few species reach arctic-alpine zones in both hemispheres. Approximately 86 Selaginella species occur in Africa, Madagascar, and neighbouring islands.
Little is known about the dispersal and establishment of these heterosporous plants. The transportation of soil containing spores by animals and by the washing away of soil cannot be ruled out. The decumbent stems of the plants ensure their dispersal on a local scale.
Uses and cultural aspects
Apart from it being used as a horticultural subject, either for outdoor or indoor cultivation, Selaginella kraussiana has no known cultural uses.
Growing Selaginella kraussiana
The delicate nature of Selaginella kraussiana and its prostrate habit make it an ideal companion plant for cultivation in moist shaded areas. If utilized as an outdoor plant, Selaginella kraussiana is best cultivated in the southern and eastern parts of the country with higher rainfall and a more temperate frost-free climate. Cultivation in zones prone to frost should be avoided unless the plants are cultivated in protected areas. S. kraussiana is a shade-loving plant and is best cultivated in such conditions. The plants will, however, tolerate higher light intensities and exposure to periods of full sunlight, but the soils must then be kept wet. The species will tolerate slightly dry conditions for short periods. When exposed to higher light intensities the plants tend to turn yellowish.
Selaginella kraussiana is also suitable for cultivation indoors. This is best done in smaller containers positioned in areas receiving good, but not direct sunlight. As with cultivation outdoors, the humus-rich growing medium should be kept moist at all times.
Selaginella kraussian a can be cultivated under various conditions ranging from saturated clay soils to well-drained humus-rich soils, due to the weak and shallow root system of the plants. Available moisture and light levels will determine the successful cultivation of the species.
Propagation of S. kraussiana is best done by vegetative means. This may be done through layering or the splitting of established plants. Stems 15 cm or longer may also be laid on the ground and at intervals lightly covered with soil. This is best done during summer, the active growing period of the plant. Until established the plants should be kept moist at all times.
Selaginella kraussiana is not prone to pests and diseases.
References and further reading
- Roux, J.P. 2009. Synopsis of the Lycopodiophyta and Pteridophyta of Africa, Madagascar and neighbouring islands. Strelitzia 23. South African National Biodiversity Institute, Pretoria.
- Spohr, O.H. 1973. Ferdinand Krauss; Travel Journal/Cape to Zululand. Observations by a collector and naturalist 1838–40. A.A. Balkema, Cape Town.
|We would like to pay tribute to the author of this Plant of the Week, Dr Koos Roux, who has contributed many articles to this series over the years as a small part of his large contribution to botany in South Africa. Dr Roux who was Manager of the Compton Herbarium at Kirstenbosch was tragically killed in a hit and run accident while out cycling on 12 May 2013.
Compton Herbarium, Kirstenbosch