SOUTH AFRICAN JOURNAL OF PLANT AND SOIL

South African Journal of Plant and Soil is co-published by Taylor & Francis and NISC (Pty) Ltd Leucadendron are woody, dioecious perennials, where male and female may differ in leaf size and floral display (De Kock et al. 1994, Rebelo et al. 1995, Bond and Maze 1999). After cessation of shoot growth, the female plants form a terminal cone, which is not formed in the male counterpart. The distal involucral leaves surrounding the terminal cone are often intensely coloured, varying from red to yellow or a combination thereof (Leonhardt and Criley 1999). The colour of involucral leaves, however, is transient in nature. The involucral leaves of female yellow Leucadendron are green during the initial development of the flower head, but turn completely yellow upon anthesis. Shortly after death of the small florets of the inflorescence, the involucral leaves completely regreen (Schmeisser et al. 2010). Natural regreening of yellow plant organs is a rare phenomenon in nature, considering the vast species diversity on our planet. So far it has only been reported to occur in a few flower and floral accessory structures (Grönegress 1974, Sitte 1974, Tran et al. 1995, van Doorn 1997, Tavares et al. 1998, Salopek-Sondi et al. 2002), some fruit (Coggins and Lewis 1962, Devide and Ljubesic 1974, Mayfield and Huff 1986, Prebeg et al. 2008) and, contrary to belief (van Doorn 2005), even in leaves (Ikeda 1979, Koiwa et al. 1986). The natural regreening of the leaves of Euonymus and Buxus as reported by Ikeda (1979) and Koiwa et al. (1986) is related to the seasonal shift from winter to summer. The degreening and regreening encountered in Leucadendron, unlike Euonymus and Buxus, is directly linked to the development of the inflorescence, rather than directly to environmental conditions. The degreening of involucral leaves, due to its close link to floral development, is thought to play a significant role in the pollination syndrome (Schmeisser et al. 2010). Of all the studies dealing with the natural regreening of plant structures, only a few address the significance of the regreening phenomenon, in terms of what the plant stands to gain by prolonging the longevity of these structures. Although mature green leaves are generally the main source of photosynthates, green floral structures (both sterile and fertile) are reported to significantly contribute to carbon fixation (Aschan et al. 2005). Therefore a possible function of regreening would be to contribute to the net carbon gain of the plant, especially during fruit development. The regreened sepals of Helleborus niger were shown to provide a significant amount of photosynthates during initial fruit development in spring, when mature leaves were not yet present (Salopek-Sondi et al. 2000, Aschan et al. 2005, Herrera 2005). Indeed, in many of the species mentioned, the perianth, spathe or sepals do not regreen unless successful pollination and subsequent fruit development takes place (Grönegress 1974, Sitte 1974, Salopek-Sondi et al. 2002). Leucadendron differ in this respect, as involucral leaves will regreen irrespective of successful pollination. Regreening of female involucral leaves appears to be the rule and occurs as a response to the senescence of the small florets. Any factor that results in the expedited death of the florets will cause the involucral leaves to regreen sooner (Schmeisser et al. 2010). It is uncertain to what extent the involucral leaves contribute to the carbon budget of the plant. If the primary function The function of regreening in yellow female Leucadendron (Proteaceae)