Shade-tolerant flowering plants in the Southern African flora : morphology, adaptions and horticultural application

Abstract

Shade plants (sciophytes) may be regarded as stress-tolerant and are classified either as obligate or facultative. Most southern African sciophytes are facultative. Two broad adaptive strategies are employed by shade plants. Optimal use is made of available energy and energy is conserved. Climatic, topographical and ecological factors are inseperable from the presence of shade. Temperature, humidity and nutrient status may even play a more important role in plant adaptation than the presence of shade. There are 1105 plants listed in the database. As might be expected of forest undergrowth in general, many southern African sciophytes are herbaceous perennials. This group forms 23% of the total number. Equivalent in represententatives, are the xerophytic plants (succulents) also 23%. These two groups together thus forms 43% of the shade plants. The second largest group are the woody plants which in total makes up 30% if the shrubs, trees and climbers are combined. The third largest group are the geophytic (bulbous) plants and forms 14% of the shade plants. All other groups make up less than 5% of the total. Many of the attributes encountered in sciophytes occurring in tropical rainforests are also found in the drier, southern African climate. The red undersurface of leaves which has hitherto only been described in herbaceous species, is described here in succulent, southern African sciophytes. The literature relating to anatomical and physiological adaptations of sciophytes is surveyed and discussed. Of particular interest is the phenomenon of sunflecks. Morphological adaptions include heart-shaped leaves, or variations thereof. The arrangements of stems and leaves to maximize the use of available light are architectural adaptations that are also discussed. Sciophytes practice many conservative reproductive strategies. Small and inconspicuous flowers are the norm. Where flowering in the shade does indeed occur, reproductive structures are adapted to local pollinating agents. Hybridisation of both herbaceous and succulent sciophytes is a common, natural phenomenon. Throughout the description of the adaptations, the applications thereof in horticultural terms have been highlighted where possible. The application is printed in bold letters directly following the adaptation described in the text. The practical side of shade gardening is discussed, highlighting and describing several southern African plants from different growth groups and situations. A database has been compiled, listing the southern African shade plants. As much as possible information on each plant concerning the names, distribution, description, uses, growth requirements and other additional general information has been made available in this database. Pre-selected combinations are printed out, for instance plants for specific horticultural uses or certain climatic conditions. Any other selected fields can be retrieved by the user according to his needs and choice directly from the database. The database should also be updated and supplemented with new information on each plant, as well as adding new plants.