Jooste Michelle, Dreyer Léanne L, Oberlander Kenneth C
Department of Botany and Zoology, University of Stellenbosch, Private Bag X1, Matieland, 7602, South Africa.
Department Conservation Ecology and Entomology, Stellenbosch University, Private Bag X1, Matieland, 7602, South Africa.
BMC Evol Biol. 2016 Oct 22;16(1):225. doi: 10.1186/s12862-016-0792-z.
The southern African Oxalis radiation is extremely morphologically variable. Despite recent progress in the phylogenetics of the genus, there are few morphological synapomorphies supporting DNA-based clades. Leaflet anatomy can provide an understudied and potentially valuable source of information on the evolutionary history and systematics of this lineage. Fifty-nine leaflet anatomical traits of 109 southern African Oxalis species were assessed in search of phylogenetically significant characters that delineate clades.
A combination of 6 leaflet anatomical traits (stomatal position, adaxial epidermal cells, abaxial epidermal cells, mesophyll, sheath around vascular tissue, degree of leaflet conduplication) clearly support various clades defined by previous DNA-based phylogenetic work. Other, mostly continuous leaflet anatomical traits were highly variable and showed less phylogenetic pattern.
Major and unexpected findings include the transition from ancestral hypostomatic leaflets to adaxially-located stomata in the vast majority of southern African Oxalis, the loss of semi-swollen AB epidermal cells and the gain of swollen adaxial and abaxial epidermal cells in selected clades, and multiple changes from ancestral bifacial mesophyll to isobilateral or homogenous mesophyll types. The information gathered in this study will aid in the taxonomic revision of this speciose member of the Greater Cape Floristic Region and provide a basis for future hypotheses regarding its radiation.
南部非洲酢浆草属植物在形态上具有极大的变异性。尽管该属植物的系统发育学研究近来取得了进展，但支持基于DNA的分支的形态学共衍征却很少。小叶解剖结构可能为这一分支的进化历史和系统学提供一个尚未充分研究但潜在价值很高的信息来源。为了寻找能够区分分支的具有系统发育意义的特征，对109种南部非洲酢浆草属植物的59个小叶解剖特征进行了评估。
6个小叶解剖特征（气孔位置、近轴表皮细胞、远轴表皮细胞、叶肉、维管组织周围的鞘、小叶对折程度）的组合明确支持了先前基于DNA的系统发育研究定义的各个分支。其他大多为连续的小叶解剖特征变化很大，显示出较少的系统发育模式。
主要的意外发现包括：在绝大多数南部非洲酢浆草属植物中，从祖先的下气孔小叶过渡到近轴面有气孔；在某些分支中，半肿胀的远轴和近轴表皮细胞消失，取而代之的是肿胀的近轴和远轴表皮细胞；以及从祖先的异面叶肉向等面叶或同质叶肉类型的多次转变。本研究收集的信息将有助于对开普植物区系这一物种丰富的成员进行分类修订，并为其辐射进化的未来假说提供依据。
