A monograph study of the genus Widdringtonia endl.

Abstract

The Gymnosperms in the Republic of South Africa are represented by five indigenous genera, one of which is Widdringtonia Endl. Widdringtonia generally occurs on eastern mountain ranges and their subsidiary mountain chains running from Malawi down Africa to the eas-'G0rn Cape Province and thence on +- oouthern and western coastal ranges ~ the Cedar-be~ in the Westsm Ca:pe Province. As the previous key to the genus compiled by Stapf and the delimitations of the taxa arc unsatisfactory and little was lmown of the anatomy and cytology, the genus has been revised. An historical account of tho existing literature on Widdringtonia is given. The genus is fairly uniform in its environmental requirements and its distribution appears to be limited by mean annual temperature, rainfall and soil. A morphological study of the root, stem, leaf, cones, seed and seedling was undertaken. Identification of tho various taxa is not possible on the basis of transverse sections through the primary root, stem and juvenile leaf. Regeneration of the stem has been observed to take place in the shrubby growth-forms of W. cupressoides (L.) Endl. sens. lat. Permanent slides for a xylotiomical study of the wood of all the taxa were obtained and examined. These results were compared with those of Greguss,1956. Contary to his findings, no means of distinguishing between tho wood of the various species was found. Two types of mature adult scale-like leaves can be recognised. Since the number of ovules per scale (or per cone) varies greatly in all taxa, this characteristic formerly used by Stapf, 1933, is of little taxonomic value. Chemical relationships and distribution of fossils indicate that Widdringtonia may have originated in the northern hemisphere and that the genus is not closely related to Callitris, generally considered to be southern in origin. The chromosomes of Widdringtonia are small, few in number and stain well. They arc however, difficult to count as tho chromosomes do not spread easily. Thus the diploid number of 16 chromosomes for Widdringtonia is tentatively suggested but may be inaccurate. W. caffra Berg, previously overlooked, is considered synonymous with W. cupressoides (L.) Endl. Tho nomen dubiu.m w. juniporoides (L.) Endl. is replaced by w. cedarbergensis Marsh. A critical study of a wide range of both living and dried material of Widdringtonia Endl. resulted in the recognition of throe species only: w. cedarbergensis Marsh, W. cupressoides (L.) Endl. and schwarzii (Marl.) Mast. The six species recognised by Stapf, 1933, cannot be upheld, since the species W. dracomontana Stapf, W. whytei Rendle, and stipitata Stapf are all regarded as synonymous with w. cupressoides (L.) Endl.