Rundel P. W., Cowling R. M., Esler K. J., Mustart P. M., van Jaarsveld E., Bezuidenhout H., Winter growth phenology and leaf orientation in Pachypodium namaquanum (Apocynaceae) in the succulent karoo of the Richtersveld, South Africa, Oecologia, 1995, 101(4):472-477, doi: 10.1007/BF00329426
The study describes seasonal leaf development in Pachypodium namaquanum in the Richtersveld and the relationship between northward leaf inclination and winter radiation absorption. Calendar months refer to the South African site and Southern Hemisphere seasons.