The systematic significance of the fruit and seed morphology and anatomy in selected Oxalis L. (Oxalidaceae) species

[摘要] At present a proper systematic classification of the southern African members of Oxalis L.(Oxalidaceae) does not exist. The most recent and comprehensive revision of the genus basedon macro-morphological characters is out-dated (published 60 years ago (Salter, 1944)). Theexternal morphology of the flowers of the southern African Oxalis species is reasonably wellstudied,but little is known about the anatomy thereof. A pilot study of fruit and seedmorphology and anatomy of nine selected southern African Oxalis species (Obone, 2003)already revealed some trends to demarcate two main groups. This confirmed the systematicvalue of some of the characters already proposed by Salter (1944).The aim of the present study was to assess the potential systematic value of fruit and seedmorphology and anatomy of 32 Oxalis species. The selection was done such that the includedspecies would represent the main sections proposed by Salter (1944), the pollen typesproposed by Dreyer (1996) and the different clades revealed by the phylogenetic treecompiled by Oberlander et al. (2004).Although the species sampling was very low (20% of the southern African taxa), 35potentially informative characters were identified in fruit and seed morphology and anatomy.These characters may be grouped into three character types, namely autapomorphiccharacters, randomly distributed characters and systematically informative characters. Thefirst two character types were particularly useful in species-specific characterization. Thethird group of linked characters could be used to demarcate two major groups of species,those producing endospermous seeds and those producing exendospermous seeds. The threetypes of characters may prove to be taxonomically informative if more species-inclusivestudies are performed.The cluster analysis strongly supported the demarcation of endospermous andexendospermous groups with 100% bootstrap support. Low bootstrap values were observedfor subgroups within each of the major groups. This is probably due to low taxon sampling.Therefore clustering based on fruit and seed morphology should be considered with extremecaution within the two groups. Despite these limitations of sample size, fruit and seedmorphological and anatomical characters have proven to be systematically informative at theinfra-generic level.

[发布机构] Stellenbosch University